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GUIDE-O-LEARN

MOTOR MECHANICS

 FUELS  ENGINE OIL  TRANSMISSION   SUSPENSION  and TYRES

 GLOSSARY AUTOMOTIVE TERMS

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TABLE OF CONTENTS Page

ENGINE SECTION Taking in air, Squeezing the air, Burning the air-fuel mixture, Getting rid of the burnt gases Engine layouts The difference between 4 and 2 stroke Spark-ignition engine components How 2 stroke engines work How 4 stroke engines work Compression-ignition engine components 4 stroke diesel engines 2 stroke diesel engines "Clean" diesels? Toyota's D-Cat and DPNR Interference versus non-interference engines Top Dead Centre (TDC) and Checking ignition timing Check the timing marks first Timing marks on cam belt pulleys Spark plugs How does the fuel-air mix happen? Carburettors How they work Float and diaphragm chambers Carb icing Complexity for the sake of it Different types of injector systems ECU maps Valves and valve mechanisms Spring-return valves valves 16v and the other names you'll find on the back of a Variable valve timing Rotary / Wankel engines Engine cooling systems Oil cooling Water cooling The complexities of water cooling FUEL SECTION Petrol E10 Ethanol Fuel: you're using it right now Detonation, pre-ignition, pinking, pinging and knocking

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Octane ratings - how to stop detonation Measuring octane - RON, MON What factors affect detonation? Octane and altitude Octane and power Octane and petrol mileage Octane boosters Lead Replacement Petrol (LRP) and valve seats Fuel filters - without them, all this means nothing Why filter the fuel? Won't the debris just burn? Why change the filter? Where is my ? The 'sock' filter The carburettor internal filter

ENGINE OIL SECTION What does my oil actually do? What do the numbers around the 'W' mean? For example 5W40? A quick guide to the different grades of oil Mineral or synthetic? Synthetics Pure synthetics Flushing oils Do I need a flushing oil? Engine oil categories Engine oil grades How often should I change my oil? Maintenance minders - when the car tells you when to change the oil What else happens when I change the oil? Checking the oil in your engine, and topping up What happens when an engine is overfilled with oil? What's the best way to check the oil level? Can I use oil in my ? Oil filters and filtration TRANSMISSION SECTION Manual gearboxes - what, why and how? How gears work Making gears work together to make a gearbox The synchromesh - why you don't need to double-clutch What about reverse? Crash gearboxes or dog boxes Before the gearbox - the clutch 'basket' clutches Automatic gearboxes How planetary gear-sets work Locking planetary gear-set components

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The automatic gearbox hydraulic system - how it changes gears Parking Torque converters TipTronic® Gearboxes CVT - continuously variable transmission Toroidal CVT (Nissan Extroid) Differentials Is there a differential on each ? Open differentials Limited-slip differentials Torsen differentials How does a Torsen 'sense' torque? Locking differentials Viscous couplings Hydraulic clutch couplings 2WD - two- drive 4WD - four-wheel drive AWD - all-wheel drive type 1 AWD - all-wheel drive type 2 FWD, RWD, FE, ME, RE

BRAKES SECTION Brakes - what do they do? Thermodynamics, fade and drilled rotors The different types of brakes wheel brakes Drum brakes - single leading edge Drum brakes - double leading edge Disc brakes Brake pad compounds Brake squeal Brake actuators Single-circuit hydraulic Dual-circuit -by-wire Mechanical advantage Mechanical advantage as applied to hydraulics Power brakes and master cylinders The components of a master Cross-linked brakes - why there are two brake circuits A word about handbrakes When to use handbrakes When not to use handbrakes Anti lock Braking Systems - ABS Newer generation ABS systems ABS and skid control Brake-assist and collision warning systems Other brake technologies

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Brake hoses - not just rubber Brake fluids D.O.T. ratings Brake warning lights LED replacement bulbs

SUSPENSION SECTION What does it do? Suspension types Front suspension - dependent systems Front suspension - independent systems MacPherson strut or McPherson strut Double wishbone suspension systems Coil spring type 1 Coil spring type 2 Multi-link suspension Trailing-arm suspension Twin I-beam suspension Moulton rubber suspension Transverse leaf-spring Rear suspension - dependent (linked) systems Solid-axle, leaf-spring Solid-axle, coil-spring 4-bar Derivatives of the 4-bar system De Dion suspension, or the Rear suspension - independent systems suspension Hydropneumatic suspension Digital suspension systems Ferrofluid or magneto-rheological fluid dampers - Audi Magnetic Ride Why air suspension? Bags and struts Ride height sensors Control panels Anti-roll bars (sway bars/stabilizers) Suspension bushes Sprung vs. unsprung weight Progressively wound springs Torsion bars

STEERING SECTION Basic steering components The Ackermann Angle : your wheels don't point the same direction Why 'Ackermann'?

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Steering ratios Turning circles Steering system designs: Pitman arm types Worm and sector Worm and roller Worm and nut or recirculating ball Cam and lever Steering system designs: Variable-ratio rack and pinion steering dynamics and steering - how it can all go very wrong Understeer Oversteer Counter-steering

TYRES & WHEELS SECTION How to read your tyre markings OE manufacturer letters DOT codes and the 6-year shelf life The E-mark Tyre size notations Tyre size markings Ultra high speed tyre size notations Speed ratings Load indices Car tyre types Tyre constructions Comparison of radial vs cross-ply performance A subset of tyre construction: tyre tread Tread patterns Tread depth and tread wear indicators Aquaplaning / hydroplaning Coloured dots and stripes - what’s that all about? Caster, camber, -in toe-out alignment Caster Camber Toe in and out Rotating your tyres Diagnosing problems from tyre wear Trouble Shooting Chart for Tyre Wear

GLOSSARY AUTOMOTIVE TERMS

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ENGINE SECTION back to ToC

Taking in air, Squeezing the air, Burning the air-fuel mixture, Getting rid of the burnt gases… ....is the common description for how an internal combustion engine works.

The basic way all internal combustion engines work is to take a mixture of fuel and air, compress it, ignite it either with a or by self- ignition (in the case of a diesel engine), allow the explosion of combusting gasses to force the back down and then expel the exhaust gas.

The vertical movement of the piston is converted into rotary motion in the crank via connecting rods.

The crank then goes out to the gearbox via a and clutch, and the gearbox sends the rotary motion to the wheels, driving the vehicle forwards.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 8 The diagram above illustrates these concepts. It shows an inline-4 engine with dual overhead cams. Engine layouts

Here are some illustrations of the most common types of cylinder layout you'll find in engines today.

Singles are typically used in motorbikes, chainsaws etc. V-twins are also found in motorbikes. Inline-fours are the mainstay of car engines, as well as being found in some motorbikes too such as the BMW K1200S. Inline fives used to be used a lot in Audis but have found a new home in current Volvos. The V5 is something you'll find in some VWs. The V6 has the benefits of being smoother than an inline-four but

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 9 without the fuel economy issues of a V8. Boxer engines are found in BMW motorbikes (twins) and Porsches and Subarus (fours and sixes).

The difference between 4 stroke and 2 stroke engines Almost every car sold today has a 4 stroke engine. So do a lot of motorbikes, lawnmowers, and other mechanical equipment. But 2 stroke engines are often found in smaller motorbikes, smaller lawnmowers, etc.

The difference between the two engine types is the number of times the piston moves up and down in the cylinder for a single combustion cycle. A combustion cycle is the entire process of sucking fuel and air into the piston, igniting it and expelling the exhaust.

Spark-ignition engine components Basic engine The attaches to the cylinder block. components A gasket makes a seal between them. Some cylinder blocks have passages to carry oil and coolant. 4 & 2-stroke Ports in the cylinder head or walls carry air-fuel engine mixture and exhaust gases. In 4-stroke engines, differences valves open and close the ports. A acts on a valve spring to operate the valve. Engine cams & A cam is a lobe on a , shaped to camshaft control how the valve opens and closes. The camshaft keeps all of the valves working with the correct timing and in the correct sequence. Engine power Power can be transferred from the to transfer the camshaft by timing gears, a timing chain running on sprockets, or a running on toothed pulleys. 2-stroke power The is the lower part of the cylinder transfer block. In a 2-stroke gasoline engine, air-fuel mixture flows through a transfer port from the crankcase to the .

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Scavenging In cross-flow scavenging the inlet or transfer port is opposite the exhaust port. In loop scavenging the inlet or transfer ports are within 90° of the exhaust ports. Counter The crankshaft is the main rotating component weights in the engine. The crankshaft rotates in main bearings. The flywheel stores momentum during non-power strokes. Piston The secures the piston to the components crankshaft. The piston transfers the force produced by the combustion to the crankshaft. Piston rings make a seal between the piston and the cylinder wall.

How 2 stroke engines work A 2 stroke engine is different from a 4 stroke engine in two basic ways. First, the combustion cycle is completed within a single piston stroke as opposed to two piston strokes, and second, the lubricating oil for the engine is mixed in with the petrol or fuel. In some cases, such as lawnmowers, you are expected to pre-mix the oil and petrol yourself in a container, then pour it into the . In other cases, such as small motorbikes, the bike has a secondary oil tank that you fill with 2 stroke oil and then the engine has a small pump which mixes the oil and petrol together.

The simplicity of a 2 stroke engine lies in the reed valve and the design of the piston itself. The 2 stroke piston is generally taller than the 4 stroke version, and it has two slots cut into one side of it. These slots, combined with the reed valve, are what make a 2 stroke engine work the way it does.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 11 As the piston reaches the top of its stroke, the spark plug ignites the fuel- air-oil mixture. The piston begins to retreat. As it does, the slots cut into the piston on the right begin to align with the bypass port in the cylinder wall. The receding piston pressurises the crank case which forces the reed or flapper valve to close, and at the same time forces the fuel-air-oil mixture already in the crankcase out through the piston slots and into the bypass port.

This effectively sends the mixture up the side of the cylinder and squirts it into the combustion chamber above the piston, forcing the exhaust gas to expel through the exhaust port. Once the piston begins to advance again, it generates a vacuum in the crank case. The reed or flapper valve is sucked open and a fresh charge of fuel-air-oil mix is sucked into the crank case. When the piston reaches the top of its travel, the spark plug ignites the mixture and the cycle begins again.

For the same cylinder capacity, 2 stroke engines are typically more powerful than 4 stroke versions. The disadvantage is the pollutants in the exhaust; because oil is mixed with the petrol, every 2 stroke engine expels burned oil with the exhaust. 2 stroke oils are typically designed to burn cleaner than their 4 stroke counterparts, but nevertheless, the 2 stroke engine can produce a great deal of smoke. The other disadvantage of 2 stroke engines is that they are noisy compared to 4 stroke engines. Typically the noise is described as "buzzy".

How 4 stroke engines work 4 stroke engines are typically much larger capacity than 2 stroke ones, and are more complex. Rather than relying on the simple mechanical concept of reed valves, 4 stroke engines typically have valves at the top of the combustion chamber. The simplest type has one intake and one exhaust valve. More complex engines have two of one and one of the other, or two of each.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 12 When you see "16v" on the badge on the back of a car, it means it's a 4-cylinder engine with 4 valves per cylinder - two intake and two exhaust - thus 16 valves, or "16v". The valves are opened and closed by a rotating camshaft at the top of the engine. The camshaft is driven either by gears directly from the crank, or more commonly by a timing belt.

In a 4 stroke combustion cycle, as the piston retreats on the first stroke, the intake valve is opened and the fuel-air mixture is sucked into the combustion chamber. The valve closes as the piston bottoms out. As the piston begins to advance, it compresses the fuel-air mix.

As it reaches the top of its stroke, the spark plug ignites the fuel-air mix and it burns. The expanding gasses force the piston back down on its second stroke. At the bottom of this stroke, the exhaust valve opens, and as the piston advances for a second time, it forces the spent gasses out of the exhaust port. As the piston begins to retreat again, the cycle starts over, sucking a fresh charge of fuel-air mix into the combustion chamber.

Because of the nature of 4 stroke engines, you won't often find a single-cylinder 4 stroke engine. They are found in some off-road motorbikes but they have such a thump-thump-thump motion that they require some large balancing shafts or counterweights on the crank to try to make the ride smoother. They also take a little longer to start from cold because you need to crank the single piston at least twice before a combustion cycle can start.

If there is more than one piston, the engine gets a lot smoother, starts better, and is much less thumpy. That's one of the advantages of V-6 and V-8 engines. Apart from the increased capacity, more cylinders typically results in a smoother engine because it will be more in balance.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 13 Compression-ignition engine components Basic diesel Diesel engine parts are usually heavier or more engine rugged than those of similar output gasoline components engines. Their engine blocks and cylinder blocks are usually made of cast iron. Diesel engine In a diesel engine, just air enters the combustion passages chamber first. It is then highly compressed. Fuel is injected and ignites due to heat of the compressed air. That's why diesels are called compression- ignition engines. Diesel fuel In direct injection fuel is injected directly into the delivery combustion chamber. In indirect injection fuel is sprayed into a smaller separate chamber in the cylinder head. A glow plug helps the combustion start. Direct injection Most valves in diesels are parallel to the centre-line of the engine. Small 4-stroke engines usually have one inlet and one exhaust valve per cylinder. Larger 4-stroke diesels may have two of each per cylinder. Diesel valves & Valves in diesel engines are usually operated by a components pushrod system. The camshaft is mounted in the near the crankshaft. It keeps the valves working in sequence. Diesel In uniflow scavenging air flows towards top of the scavenging cylinder. In crossflow scavenging air enters one side of cylinder, exhaust gases exit on the other. In loop scavenging air flows up in a loop across the top of the piston. Crankshaft In a 2-stroke diesel engine, the camshaft and rotation crankshaft must rotate at the same speed. So the gears driving them must be the same size. Diesel In a 4-stroke cycle, only one stroke in four delivers crankshaft energy. In a 2-stroke, it is only one stroke in two. A flywheel stores this energy to help turn the crankshaft through the non-power strokes. Diesel engine Clearance between the piston and its cylinder wall must be kept small. This is done by piston rings - expandable metal rings held in grooves in the side of the piston.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 14 4 stroke diesel engines Mechanically, 4 stroke diesel engines work identically to four- stroke petrol engines in terms of piston movement and crank rotation. The differences between them are found in the combustion cycle First, during the intake cycle, the engine only sucks air into the combustion chamber through the intake valve - not a fuel/air mix. Second, there is no spark plug. Diesel engines work on self-ignition, or detonation - the one thing you don't want in a petrol engine! At the top of the compression stroke, the air is highly compressed (over 35 bar-), and very hot (around 700 °C). The fuel is injected directly into that environment and because of the heat and pressure, it spontaneously combusts. This system is known as direct-injection. It gives the characteristic knocking sound that diesel engines make, and is also why pre-igniting petrol engines are sometimes referred to as 'dieseling'.

Petrol engines typically run compression ratios around 10:1, with lower end engines down as low as 8:1 and sportier engines up near 12:1. Diesel engines on the other hand typically run around 14:1 compression ratio and can go up as high as 25:1. Combined with the higher energy content of diesel fuel (around 10 kW per litre compared to 8.23 kW per litre of petrol), this means that the typical diesel engine is also a lot more efficient than the petrol engine, hence the much higher fuel-mileage ratings.

Because of the design of the diesel engine, the injector is the most critical part and has been subjected to hundreds of variations in both design and position. It has to be able to withstand massive pressures and temperatures, yet still deliver the fuel in a fine mist. One other component that some diesel engines have is a . From cold, some lower-tech engines can't retard the ignition enough, or get the air temperature high enough on startup for the spontaneous combustion to happen. In those engines, the glowplug is a hot wire in the top of the cylinder designed to increase the temperature of the compressed air to the point at which the fuel will combust.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 15 These engines typically have a pictograph on the dashboard that looks like a lightbulb. When starting the engine cold, you need to wait for that light to go out while the get up to temperature. In really old diesel designs, this could be as long as 10 seconds. Nowadays it's nearly instantaneous, or in the case of advanced ECM systems, not needed at all.

2 stroke diesel engines You may not know that there is such a thing as a 2 stroke diesel engine! The two-stroke cycle described above is highly beneficial for the diesel model. The major difference is the inclusion of exhaust valves at the top of the cylinder.

The burn cycle works similarly too. At the top of the piston travel, the air is hot and compressed, just like in a 4 stroke diesel. And like the 4 stroke, the injector sprays fuel in at that point and it self-combusts. As the gasses expand, the piston is forced downwards. Towards the bottom of its stroke, the exhaust valves on the top of the cylinder open. Because the gas is still expanding at this point, the combustion chamber empties itself through the open valves. At the very bottom of the power stroke, the piston uncovers the air intake and pressurised air fills the combustion chamber forcing the last remnants of the exhaust gas out. As the piston begins its compression stroke, the exhaust valves close and the air is compressed.

The other difference between a 4 stroke and 2 stroke diesel engines is that the 2 stroke variety must have a or ; remember that the air intake fills the cylinder with pressurised air. That doesn't happen without a turbocharger or a supercharger.

As with 2 stroke petrol engines, every downward piston stroke is a power stroke, meaning the 2 stroke engine has the potential to product twice as much power as its 4 stroke counterpart. Typically you'll find 2 stroke diesels in maritime engines (like those on freighters, tankers and

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 16 cruise ships) and diesel-electric trains where more power is needed for the same size of engine.

"Clean" diesels? Toyota's D-Cat and DPNR Old-fashioned diesel engines used to sound like tractors when you started them on a cold morning. They used to spew particulates out of the exhaust - and the back of the car went black. Newer diesels start much less noisily but for the most part still have some issues with particulates in the exhaust. Toyota claim to have solved this with their D-Cat and DPNR system. D-Cat stands for Diesel Clean Advanced Technology and DPNR stands for Diesel Particulate NOx Reduction. The operating principle is fairly sound.

D-Cat is an advanced computer-controlled system for cleaning diesel exhaust gasses which relies on the DPNR catalyser. This is a combination of particle filters and normal gas-reduction catalysing metals that remove particulates, sulphur dioxide (SO2) and nitrogen dioxide (NO2) from the exhaust gasses. A sensor measure can tell when these filters are nearly full at which point a fifth diesel-injector sprays a little fuel directly into the . Combined with the exhaust gas recirculation system, this results in all the collected pollutants being burned off, cleaning the filter in the process. DPNR requires ultra-low sulphur diesel (ULSD) to work properly.

Interference versus non-interference engines

It's worth mentioning the two sub-types of 4 stroke engine at this point. Because the valves always open inwards, into the combustion chamber, they take up some space at the top of the chamber.

In an interference engine, the position of the piston at the top of its stroke will occupy the same physical space that the open valves do whilst the piston is at the bottom of its stroke.

In an interference engine, if the timing belt breaks, at least one set of valves will stop in the open position and the momentum of the engine will ram the piston in that

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 17 cylinder up into the valves requiring a very expensive engine repair or replacement. In a non-interference engine, the valves do not occupy any space that the piston could move into, so if your timing belt snaps on one of these engines, in 99% of cases you won't suffer any valve damage because the piston cannot physically touch the open valves. The picture above shows the difference between the two types. On the left, circled, is where the open valve interferes with the position of the piston at the top of its travel. On the right, a non-interference engine shows there is still a gap at the same point (exaggerated for the picture).

Top Dead Centre (TDC) and ignition timing When a piston in an engine reaches the top of its travel, that point is known as Top Dead Centre or TDC. This is important to know because no engine actually fires the spark plug with the pistons at TDC. More often than not, they fire slightly before TDC. So how does your work, and what is ignition timing all about?

Generating the spark is the easy part. The electrical system in your car supplies voltage to your coil and ignition unit. The engine will have a trigger for each cylinder, be it a mechanical trigger (points), electronic module or crank trigger. Whatever it is, at that point, the engine effectively sends a signal to the coil to discharge into the high voltage system. That charge travels into the cap and is routed to the relevant spark plug where it is turned into a spark.

The key to this, though, is the timing of the spark in relation to the position of the piston in the cylinder. This is why ignition timing is important. If the spark ignites the fuel-air mixture too soon, the result is basically the same as detonation and is bad for all the mechanical components of your engine. If the spark comes along too late, it will try to ignite the fuel-air mixture after the piston has already started to recede down the cylinder, which is inefficient and loses power.

Timing the spark nowadays is usually done by the engine management system. It measures airflow and ambient temperature, and takes input from knock sensors and literally dozens of sensors all over the engine. It then has an ignition timing map built into its memory and it cross- references the input from all the sensors to determine the precise time that it should fire the spark plug, based on the ignition timing map. At 3000rpm, in a 4 cylinder engine, it does this about 100 times a second.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 18 In older systems, the spark timing was done using simple mechanical systems which did not have the ability to compensate for all the variables involved in a running combustion engine.

Typically, as an engine revs faster, the ignition timing needs to advance because the spark needs to get to the cylinder more quickly. This is because the fuel-air mix takes a finite amount of time to combust. It won't burn any quicker or slower for any given engine speed. So for higher speeds, the mixture needs to be ignited earlier in the cycle to ensure that it begins to burn at the optimum timing point. In modern systems, this is all taken into account in the ignition timing map. On older mechanical system, they used mechanical or vacuum advance systems, so that the more vacuum generated in the intake manifold (due to the engine running quicker), the more advanced the timing became.

Checking ignition timing Despite the speed that an engine turns, it is possible to check the ignition timing on an engine using an ignition . Timing lights are typically strobe lights. They work by being connected to the battery directly and then having an induction coil clamped around one of the spark plug leads - normally the first or last cylinder in the engine depending on the manufacturer. When the engine fires the spark plug for that cylinder, the inductive loop detects the current in the wire and flashes the strobe in the timing light once. So if the engine is ticking over at 1100rpm, the strobe will flash 550 times a minute (4 stroke engine, remember?).

How does this help you see the timing of an engine? It's simple! You must have seen strobe lights working somewhere – maybe at a rave, or a stage show. They're used to effectively freeze the position of something in time and space by illuminating it only at a certain point and for a fraction of a second. Shooting a strobe at someone walking in a dark room will result in you seeing them walk as if they were a flip- book animation on a reel of film. This effect is what's used to visualise the timing of your engine. Somewhere on the front of the engine there

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 19 will be a notch near one of the timing belt pulleys and stamped into the metal next to it will be timing marks in degrees. On the pulley itself there will be a bump, a recess or a white-painted blob. Point the timing light down towards the timing belt pulley - remember it fires once for each firing of the cylinders. Each time it fires, the white blob on the pulley should be at the same position in its rotation - the strobe fires once for each ignition spark at which point the mark should be in the same place. The effect is that the whole pulley, timing mark and all, is now standing still in the strobe light. The mark on the pulley will line up with one of the degree marks stamped on the engine, so for example if the white dot always aligns with the 10° mark, it means your engine is firing at 10 degrees before TDC. When you rev the engine, the timing will change so the mark will move closer or further away from the TDC mark depending on how fast the engine is spinning.

Note that in some engines, the two marks are simply painted or stamped, and there are no degree markings. In this case, the marks align when the first piston is exactly at TDC.

Check the timing marks first Sometimes, crank timing marks can be inaccurate so you should confirm that your TDC marker is actually TDC before changing the timing.

Timing marks on cam belt pulleys The same timing marks exist stamped into the metal near, and on the pulley on, the end of the cam. Essentially these marks are used to line up the cam to the correct position when you're changing the timing belt. You must make sure the engine is rotated to TDC and that the cams are properly aligned too. If not, the cams will spin permanently out-of- synch with the engine crank and the engine will run badly, if at all.

Spark plugs An engine without a spark plug is useless, unless it's a diesel engine in which case it uses a glowplug instead. With regular petrol engines, the next topic to get to grips with is the spark plug. It does exactly what it says - it's a plug that generates a spark.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 20 Sparkplugs are not all exactly the same, though. They'll all do the job but the more you pay, the better the plug. However, all spark plugs share the same basic design and construction.

The high voltage from a vehicle's high-tension electrical system is fed into the terminal at the top of the spark plug. It travels down through the core of the plug (normally via some noise-suppression components to prevent electrical noise) and arrives at the centre electrode at the bottom where it jumps to the ground electrode, creating a spark.

The crush washer is designed to be crushed by tightening the spark plug down when it's screwed into the cylinder head, and it helps to keep the screw threads under tension to stop the spark plug from shaking loose or backing out. The insulator basically keeps the high-tension charge away from the cylinder head so that the spark plug doesn't ground before it gets a chance to generate the spark.

The type of plug illustrated here is known as a projected nose type plug, because the tip extends below the bottom of the spark plug itself. The other main type of spark plug has the centre electrode recessed into the plug itself and merely grounds to the collar at the bottom. The advantage of the projected nose type is that the spark is better exposed to the fuel-air mixture.

Ground electrode (ground strap) types. There are many different types of grounding electrodes in spark plug designs nowadays, from 'Y' shaped electrodes (like SplitFire plugs) to grooved electrodes like the ones you'll find on Champion plugs all the way up to triple- electrode plugs like the high-end Bosch items. They're all designed to

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 21 try to get a better spark, and to that end, you'll now find all sorts of exotic materials turning up too. Titanium plugs, for example, have better electrical conductivity than brass and steel plugs, and the theory is that they generate a stronger, more reliable spark.

Gapping a spark plug. Gapping a spark plug is the process of ensuring the gap between the two electrodes is correct for the type of engine the plug is going to be used in. Too large a gap and the spark will be weak. Too small and the spark might jump across the gap too early. Generally speaking, the factory-set spark plug gap is optimal, but if you're running an older engine, or a highly tuned engine, then you need to pay attention to the gap. Feeler gauges are used to measure the gap, and a gapping tool is used to bend the outer electrode so that the gap is correct.

Heat ranges. Something that is often overlooked in spark plugs is their heat rating or heat range. The term "heat range" refers to the relative temperature of the tip of the spark plug when it is working. The hot and cold classifications often cause confusion because a 'hot' spark plug is normally used in a 'cold' (low horsepower) engine and vice versa. The term actually refers to the thermal characteristics of the plug itself, specifically its ability to dissipate heat into the cooling system. A cold plug can get rid of heat very quickly and should be used in engines that run hot and lean. A hot plug takes longer to cool down and should be used in lower compression engines where heat needs to be retained to prevent combustion by-product build-up.

How does the fuel-air mix happen? The fuel-air mix or fuel-air charge is fundamental to the operation of internal combustion engines. The fuel and air are mixed in one of two main ways. The old-fashioned method is to use a carburettor, whilst the new-tech approach is to use fuel injectors. The basic purpose is the same though, and that is to mix the fuel and air together in proportions that keep the engine running. Too little fuel and the engine runs 'lean' which makes it run hot. Too much fuel and it runs 'rich' which conversely makes the engine run cooler. Running rich can also result in fouled up spark plugs, flooded engines and stalling, not to mention wasting fuel. Finding the right balance normally involves the combustion of about 10 milligrams of petrol for each combustion stroke.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 22 Carburettors Advantages: analogue and very predictable fuelling behaviour, simple and inexpensive to build and maintain .Disadvantages: carburettor icing in the venturi, imprecise fuel metering, float chambers don't work well if they're not the right way up.

How they work A carburettor is basically a shaped tube. The shape of the tube is designed to swirl the incoming air and generate a vacuum in a section called the venturi pipe (or just the venturi). In the side of the venturi is a fuel jet which is a tiny hole connected to the float chamber via a pipe. It's normally made of brass and has a miniscule hole in the end of it which determines the flow of fuel through it. In more complex carburettors, this is an adjustable needle valve where a screw on the outside of the carburettors can screw a needle in and out of the valve to give some tuning control over the fuel flow.

The fuel is pulled through the jet by the vacuum created in the venturi. At the bottom of the tube is a plate or throttle butterfly which is a flat circular plate that pivots along its centreline.

It is connected mechanically to the accelerator pedal or twist-grip throttle via the throttle cable. The more you push on the accelerator or twist open the throttle, the more the throttle butterfly opens. This allows more air in which creates more vacuum, which draws more fuel through the fuel jet and gives a larger fuel-air charge to the cylinder, resulting in acceleration.

When the throttle is closed, the throttle butterfly in the carburettor is also closed. This means the engine is trying to suck fuel-air mix and generating a vacuum behind the butterfly valve so the regular fuel jet won't work. To allow the engine to idle without shutting off completely, a second fuel jet known as the idle valve is screwed into the venturi downwind of the throttle butterfly. This allows just enough fuel to get into the cylinders to keep the engine ticking over.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 23 Float and diaphragm chambers To make sure a carburettor has a good, constant supply of fuel to be sucked through the fuel jets, it has a float chamber or float bowl. This is a reservoir of petrol that is constantly topped up from the fuel tank. Petrol goes through an inline filter and a strainer to make sure it's clean of contaminants and is then deposited into the float chamber. A sealed plastic box is pivoted at one end and floats on top of the fuel. Not surprisingly, this is called the float. A simple lever connects to the float and controls a valve on the fuel intake line. As the fuel drops in the float chamber, the float drops with it which opens the valve and allows more fuel in. As the level goes up, the float goes up and the valve is restricted. This means that the level in the float chamber is kept constant no matter how much fuel the carburettor is demanding through the fuel jets.

The quicker the level tries to drop, the more the intake valve is opened and the more petrol comes in to keep the fuel level up. This is why carburettors don't work too well when they're tipped over - the float chamber leaks or empties out resulting in a fuel spill - something you don't get with injectors. To combat this, another type of chamber is used where carburettors can't be guaranteed to be upright (like in chainsaws). These use diaphragm chambers instead. The principle is more or less the same. The chamber is full of fuel and has a rubber diaphragm across the top of it with the other side exposed to ambient air pressure. As the fuel level drops in the chamber, the outside air pressure forces the diaphragm down. Because it's connected to an intake valve in the same way that the float is in a float chamber, as the diaphragm is sucked inwards, it opens the intake valve and more fuel is let in to replenish the chamber. Diaphragm chambers are normally spill- proof.

Carb icing One of the problems with the spinning, compressing, vacuum- generating properties of the venturi is that it cools the air in the process. Whilst this is good for the engine (colder air is denser and burns better in a fuel-air mix), in humid environments, especially cool, humid environments, it can result in carburettor icing. When this happens, water vapour in the air freezes as it cools and sticks to the inside of the venturi. This can result in the opening becoming restricted or cut off completely. When carbs ice up, engines stop. In aircraft engines, there is a control in the cockpit called "carb heat" which either uses electrical

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 24 heating elements to heat up the venturi to prevent icing, or reroutes hot air from around the exhausts back into the carburettor intakes.

In , we don't have "carb heat" but instead there's normally a heat shield over the connected via a pipe to a temperature- controlled valve at the . When it’s cold, the valve is open and the air filter draws warm air from over the exhaust manifold and feeds it into the carburettor. As the temperature warms up, the valve closes and the carburettor gets cooler air because the risk of icing has reduced. The symptoms of carb icing are easy to diagnose. First, the engine bogs down at high throttle, then it loses power and ultimately could stall completely. If you stop on the side of the road and wait for a couple of minutes, the engine will start and run normally. This is because with the engine off, the heat from the engine warms up the carbs and melts the ice so that when you try to start it up again, everything is fine.

Complexity for the sake of it As car engines evolved, carburettors had to evolve to cope with the various demands. It's not unusual to find five-circuit carburettors which have become so complex that they're a nightmare to design, build and maintain. That contradicts one of the carburettor’s advantages, which was that they were simple. Why five circuits? The main circuit is the one which provides day-to-day running capability. It's enlarged by accelerator and load (or enrichment) circuits which can vary the fuelling to accommodate sudden acceleration or the need for more power (like driving uphill). The accelerator circuit also adds a second butterfly valve in most cases which only opens at 70% throttle or more. Then there's the choke circuit designed to provide extra fuel with the closed when the engine is cold, allowing it to start, and finally the idle circuit which does the same thing but when the engine is warm, to keep it going. On top of all of this, with the introduction of stricter emissions requirements came catalytic converters, and these expensive boxes of rare metals don't work well unless the fuel-air ratio is very carefully controlled. And that's something carburettors just couldn't keep up with. It is hardly surprising that this mechanical complexity gave way to fuel injection.

Fuel injection Advantages: precise and variable fuel metering, better fuel efficiency and better emissions.Disadvantages: fairly complex engineering that isn't very user-friendly. Binary on/off functionality at low throttles, which

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 25 is especially noticeable on motorbikes where the throttle becomes 'snatchy' and it becomes hard to ride smoothly at low speed.

How it works Compared to carburettors, fuel injectors themselves are incredibly simple. They are basically electro-mechanically operated needle valves. When a current is passed through the injector electromagnetic coil, the valve opens and the fuel pressure forces petrol through the spray tip and out of the diffuser nozzle, atomising it as it does so. When current is removed, the combination of a spring and fuel back-pressure causes the needle valve to close.

This gives an audible 'tick' noise when it happens, which is why even a quiet fuel-injected engine has a soft but rapid tick-tick-tick-tick noise as the injectors fire. This on-off cycle time is known as the pulse width. Varying the pulse width determines how much fuel can flow through the injectors. When you ask for more throttle either via the accelerator pedal or twist-grip (on a motorbike) you're opening a butterfly valve similar to the one in a carburettor. This lets more air into the intake system and the position of the throttle is measured with a potentiometer.

The (ECU) gets a reading from this potentiometer and "sees" that you've opened the throttle. In response the ECU increases the injector pulse width to allow more fuel to be sprayed by the injectors. Downwind of the throttle body is a mass airflow sensor. This is normally a heated wire. The more air that flows past it, the quicker it dissipates heat and the more current it needs to remain warm. The ECU can continually measure this current to determine if the fuel-air mix is correct and it can adjust the fuel flow through the injectors accordingly. On top of this, the ECU also looks at data coming from the oxygen (lambda) sensors in the exhaust. These tell the ECU how much oxygen is in the exhaust so it can automatically adjust for rich- or lean-running.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 26 Different types of injector systems When fuel-injection was first introduced, it was fairly simple and used a single injector in the throttle body. Basically it was a carburettor- derivative, but instead of the induction vacuum sucking fuel into the venturi, an injector forced fuel into the airflow. This was known as throttle-body fuel-injection, or single-point fuel-injection.

As engine design advanced, the single-point system was phased out and replaced with multi-point or multi-port fuel-injection. In this design, there is one injector for each cylinder, normally screwed into the intake manifold and aimed right at the intake valve. Because fuel is only sprayed when the intake valve is open, this system provides more accurate fuel-metering and a quicker throttle response. Typically, multi- point injection systems have one more injector for cold-starting which sprays extra fuel into the intake manifold upstream of the regular injectors, to provide a richer fuel-air mix for cold starting.

A coolant temperature sensor feeds information back to the ECU to determine when this extra injector should be used.

As you would expect, though, technology marches on! The latest technology is direct injection, also known as GDI (gasoline direct injection). This is similar to multi-point injection except that the injectors are moved into the combustion chambers themselves rather than the intake manifold. This is nearly identical to the direct injection system used in diesel engines. Essentially, the intake valve only allows air into the combustion chamber and the fuel is sprayed in directly through a high-pressure, heat-resistant injector. The fuel and air are mixed inside the combustion chamber itself due to the positions of the intake valve, injector tip and top of the piston crown. The piston crown in these engines is normally designed to create a swirling vortex to help mix the fuel and air before combustion, as well as having a cavity in it for ultra- lean-burn conditions.

The ECU controls the amount of fuel injected, based on the airflow into the engine and demand. It operates a direct injection engine in one of three modes: Full power mode is basically foot-to-the-floor driving. The fuel-air ratio is made richer and the injectors spray the fuel in during the piston intake stroke. In stoichiometric mode the fuel-air ratio is leaned off a little. The fuel is still sprayed in during the piston intake stroke but the burn is a lot cleaner and the ECU chooses this mode when the load

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 27 on the engine is slightly higher than normal, for example during acceleration from a stop.

Finally, when you're cruising with very little engine load (for example when you're on a motorway with no traffic), the ECU will choose an ultra lean mode. In this mode, the fuel is injected later on in the 4 stroke cycle - as the piston is moving up its compression stroke. This forces the fuel-air charge right up next to the tip of the spark plug for the best burn conditions and the combustion itself takes place partly in the cylinder and partly in the shaped piston crown mentioned previously.

ECU maps The ECU receives a wide number of sensor readings from all over the engine. Built into the ECU is a fuelling and ignition map which is basically a gigantic table of numbers. It's like a lookup table that the ECU uses to determine injector pulse width, spark timing (and on some engines, the variable valve timing). So the ECU receives a set of values from all its sensors, which it then looks up in the fuelling and ignition map.

At the point where all these numbers coincide, there is final number which the ECU uses to set the injector pulse width. These are the manufacturer's fuelling routines.

Valves and valve mechanisms Valves let the fuel-air mixture into the cylinder, and let the exhaust out. Seems simple enough, but there are some interesting differences in the various types of valve mechanism.

Spring-return valves Spring return valves are the most commonly-used and most basic type of valve-train in engines today. Their operation is simplicity itself and there are only really three variations of the same style. The basic premise is that the spinning camshaft operates the valves by pushing them open, and valve return springs force them closed. The cam lobes either operate directly on the top of the valve itself, or in some cases, on a rocker arm which pivots and pushes on the top of the valve.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 28 The three variations of this type of valve-train are based on the combination of rocker arms and the position of the camshaft. The most basic type has the camshaft at the top of the engine with the cam lobes operating directly on the tops of the valves.

The second more complex type still has the camshaft at the top of the engine, but the cam lobes operate rocker arms, which in turn pivot and operate on the tops of the valves. With some of these designs, the rocker arm is pivoted in the middle and with other designs, it's pivoted at one end and the cam lobe operates on it at the midpoint.

The third type which you'll find in some motorcycle engines and many boxer engines are pushrod-activated valves. The camshaft is directly geared off the crank at the bottom of the engine and the cam lobes push on pushrods which run up the sides of the engine. The top of the pushrod then pushes on a rocker arm, which finally pivots and operates on the top of the valve. The image here shows the three derivatives in their most basic form so you can see the differences between them.

Note that the pushrod type shows the camshaft in the wrong place simply for the purpose of getting it into the image. In reality the camshaft in this system is right at the bottom of the engine near the crank. The rocker arms shown here are also called fingers, or followers.

Tappet valves Tappet valves aren't a unique type of valve but a derivative of spring- return valves. For the most part, the direct spring return valve described above wouldn't act directly on the top of the valve itself, but rather on an oil-filled tappet. The tappet is basically an upside-down bucket that covers the top of the valve stem and contains the spring. It's normally filled with oil through a small hole when the engine is pressurised.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 29 The purpose of is two-fold. The oil in them helps to quieten the noise, and the top of the tappet gives a more uniform surface for the cam lobe to work on. From a maintenance point of view, tappets are the items which wear and are a lot easier to swap out than entire valve assemblies. The image on the right shows a simple tappet valve assembly. In the diagram, the tappet is slightly transparent so you can see the return spring inside.

16v and the other names you'll find on the back of a car "Traditional" 4-cylinder in-line engines have two valves per cylinder - one intake and one exhaust. In a 16V engine, you have four per cylinder - two intake and two exhaust. (4 valves) x (4 cylinders) = 16 valves, or 16V.

It follows that a 20V engine has 20 valves - 5 per cylinder, normally three intake and two exhaust valves. Unless you've got a 5-cylinder Audi or Volvo in which case you've still got 4 valves per cylinder. If you're in America, the thing to have now is 32V - a 32 valve engine. Basically it's a V-8 with 4 valves per cylinder. See - it's all just basic maths!

What do all these extra valves get you apart from a lot more damage if they ever go wrong? A better breathing engine. More fuel-air mix in, quicker exhaust.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 30 Variable valve timing There are a couple of novel ways by which carmakers vary the valve timing. One system used on some Honda engines is called VTEC.

VTEC (Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to have multiple . VTEC engines have an extra intake cam with its own rocker, which follows this cam. The profile on this cam keeps the intake valve open longer than the other cam profile. At low engine speeds, this rocker is not connected to any valves. At high engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves.

Rotary / Wankel engines It now becomes obvious how extremely complicated traditional 2 stroke and 4 stroke engines are. The pistons, connecting rods and crank are all there to turn up-down motion into spinning motion. Then there's the complexity of valves and valve trains,

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 31 timing belts, tappets, springs, fuel delivery systems etc.etc. There is a simpler way.

Would you believe the rotary engine essentially has only three moving parts? Conceived in 1957 by Dr. Felix Wankel, the rotary engine (also known as the Wankel Engine or Wankel Motor) works on a very simple principle.

The piston isn't a piston at all, but a three-sided convex rotor. The diagram above shows a typical example. When spun around a fixed pinion gear inside an epitrochoidal-shaped chamber, the spinning of the rotor creates the suck-squeeze-bang-blow cycle simply by its position relative to the sides of the chamber. Basically, the combination of the rotor and chamber shapes ensures that the three apexes of the rotor are always in contact with the chamber walls whilst at the same time always creating three different volumes.

As the rotor spins, each volume gets larger and smaller in turn, creating the compression and expansion volumes required for the engine to work. But how does the spinning rotor connect to the output shaft?

There's an eccentric wheel that sits in a bearing inside the rotor. The spinning rotor transfers its motion to the eccentric wheel and the centre of that wheel is connected to a crank on the output shaft. A single Wankel rotor could therefore be considered to be the equivalent of three pistons in a regular 4 stroke engine. Most rotary engines use two chambers and thus two rotors. Hence the three moving parts - the two rotors and the one output shaft. But in the Wankel engine, there are no valves required. The intake and exhaust ports are simple openings in the combustion chamber that are covered and uncovered in the correct sequence by the spinning of the rotor.

At this point, you're asking yourself - "If this is such a simple design, why doesn't everyone use it?"

Yes, the design is simple. It's also smooth. Both rotors are continuously turning in the same direction so you don't have the violent change of direction problem that a normal engine has (up/down/up/down). As well as that, the design means that the combustion cycle lasts through three quarters of each complete turn of the rotor, as compared to one quarter of every second stroke of a 4 stroke engine. But all this clever design

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 32 does have some inherent problems. Rotary engines cost more to manufacture because of the engineering tolerances required to make them work. The seals at the rotor apexes have to be very finely manufactured to prevent premature wear. (The apex seals are the equivalent of the piston rings in a normal engine).

The low compression ratio and relatively large combustion volumes mean that Wankel engines are also typically less fuel efficient than normal engines - it is typically more difficult to get these engines to pass emissions regulations. Mazda saw the benefits of rotary engines back in 1961 and have been the only manufacturer willing to spend the time, money and resources required to get a reliable, mass-producable design.

The easiest way to understand how this all works it to keep your eye on just one of the curved sides of the rotor as it spins and observe the size of the volume between it and the chamber wall. As it passes in the intake port, the volume gets larger, generating a vacuum which pulls air into the chamber. As it passes the top, fuel is injected. As it approaches the left side of the chamber, the volume gets much smaller, creating the compression.

At that point, the spark plugs fire. The combustion process causes the expansion of the gas which forces the rotor to continue its motion. Again thinking of just one side of the rotor, you'll see the volume increase in size again, to accommodate the combustion.

Finally the leading rotor apex uncovers the exhaust port and as the volume decreases again, the exhaust gasses are forced out. At this point, that one side of the rotor is now ready to start its combustion cycle again.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 33 The bigger picture of course is that while the side you were watching was going through its intake cycle, the second side was going through its compression cycle and the third side was going through its exhaust cycle. This is why a single-rotor Wankel engine is the equivalent of a three-cylinder four-stroke engine. During that entire cycle you'll have noticed the eccentric ring spinning in its bearing and in turn spinning the output crank.

Engine cooling systems It stands to reason that if you fill a metal engine with fuel and air hundreds of times a second and make the mixture explode, the whole thing is going to get pretty hot. To stop it all from melting into a fused lump of steel and aluminium, all engines have some method of keeping them cool.

Air cooling You don't see this much on car engines at all now. The most famous cars it was used on were rear-engined boxers like the original VW Beetle, Karmann Ghia, and Porsche Roadsters. It is still used a lot on motorbike engines because it's a very simple method of cooling. For air cooling to work, you need two things - fins (lots of them) and good airflow. An air-cooled engine is normally easy to spot because of the fins built into the outside of the cylinders.

The idea is simple - the fins act as heat sinks, getting hot with the engine but transferring the heat to the air as the air passes through and between them. Air-cooled engines don't work particularly well in long, hot traffic jams though, because obviously there's very little air passing over the fins. They are good in the winter when the air is coldest, but that illustrates a weak spot in the whole design. Air cooled engines can't regulate the overall temperature of the cylinder heads and engine, so the temperature tends to swing up and down depending on engine load, air temperature and forward speed.

The image on the previous page is ©Ducati and shows the engine from the Monster 695 motorbike. It's a good example of modern air-cooled

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 34 design and you can see that the fins on the engine are all angled towards the direction of travel so the air can flow through them freely.

Oil cooling To some extent, all engines have oil-cooling. It's one of the functions of the engine oil - to transfer heat away from the moving parts and back to the where fins on the outside of the sump can help transfer that heat out into the air. But for some engines, the oil system itself is designed to be a more efficient cooling system. BMW 'R' motorbikes are known for this (their nickname is 'oilheads'). As the oil moves around the engine, at some points it's directed through cooling passageways close to the cylinder bores to pick up heat. From there it goes to an oil radiator placed out in the airflow to disperse the heat into the air before returning into the core of the engine. Actually, in the case of the 'R' motorbikes, they're air- and oil-cooled as they have the air- cooling fins on the cylinders too.

Water cooling This is by far the most common method of cooling an engine down. With water cooling, a coolant mixture is pumped around pipes and passageways inside the engine separate to the oil, before passing out to a radiator. The radiator itself is made of metal, and it forces the coolant to flow through long passageways each of which have lots of metal fins attached to the outside giving a huge surface area. The coolant transfers its heat into the metal of the radiator, which in turn transfers the heat into the surrounding air through the fins - essentially just like the air-cooled engine fins. The coolant itself is normally a mixture of distilled water and an antifreeze component. The water needs to be distilled because if you use tap water, all the minerals in it will deposit on the inside of the cooling system and mess it up. The antifreeze is in the mix, obviously to stop the liquid from freezing in cold weather. If it froze up, you'd have no cooling at all and the engine would overheat and weld itself together in a matter of minutes. The antifreeze mix normally also has other chemicals in it for

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 35 corrosion resistance too and when mixed correctly it raises the boiling point of water, so even in the warmer months of the year, a cooling system always needs a water / antifreeze mix in it.

The coolant system in a typical car is under pressure once the engine is running, as a by- product of the water pump and the expansion that water undergoes as it heats up. Because of the coolant mixture, the water in the cooling system can get over 100°C without boiling which is why it's never a good idea to open the radiator cap immediately after you've turned the engine off. If you do, a superheated mixture of steam and coolant will spray out and you'll get scalded!

The complexities of water cooling Water cooling is the most common method of cooling and engine down, but it's also the most complicated. For example you don't want the coolant flowing through the radiator as soon as you start the engine. If it did, the engine would take a long time to come up to operating temperature which causes problems with the emissions systems, the drivability of the engine and the comfort of the passengers. In very cold weather, most water cooling systems are so efficient that if the coolant flowed through the radiator at startup, the engine would literally never get warm.

This is where the thermostat comes in to play. The thermostat is a small device that normally sits in the system in-line with the radiator. It is a spring-loaded valve actuated by a bimetallic spring. In layman's terms, the hotter it gets, the wider open the valve is. When you start the engine, the thermostat is cold and so it's closed. This redirects the flow of coolant back into the engine and bypasses the radiator completely - but because the cabin heater radiator is on a separate circuit, the coolant is allowed to flow through it. It has a much smaller surface area and its cooling effect is nowhere near as great. This allows the engine to build up heat quite quickly.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 36

As the coolant heats up, the thermostat begins to open and the coolant is allowed to pass out to the radiator where it dumps heat out into the air before returning to the engine block. Once the engine is fully hot, the coolant is at operating temperature and the thermostat is permanently open, redirecting almost all the coolant flow through the radiator.

It's the action of the thermostat that allows a water-cooled engine to better regulate the heat in the engine block. Unlike an air-cooled engine, the thermostat can dynamically alter the flow of coolant depending on engine load and air temperature to maintain an even temperature.

The radiator . In the past, car radiators had belt-driven fans that spun behind the radiator as fast as the engine was spinning. The fan is there to draw the warm air away from the back of the radiator to help it to work efficiently. The only problem was that the fan ran all the time the engine was running, and stopped when the engine stopped. This meant that the radiator was having air drawn through it at the same rate in freezing cold conditions as it was on a hot day, and when you parked the car, the radiator basically cooked because it had no airflow while it was cooling down. So nowadays, the radiator fan is electric and is activated by a temperature sensor in the coolant.

When the temperature gets above a certain level, the fan comes on and because it's electric, this can happen even once you've stopped the engine. This is why sometimes on a hot day, you can park, turn off, and hear the radiator fan still going. It's also the reason there are big stickers around it in the engine bay because if you park and open the bonnet to start working on the engine, the fan might come on and neatly separate you from your fingers.

The cabin heater. Most water-cooled car engines actually have a second, smaller radiator that the coolant is allowed to flow through all the time for in-car heating. It's a small heat-exchanger in the air vent system.

When you select warm air with the heater controls, you will either be allowing the coolant to flow through that radiator via an inline valve in the cooling system (this is the old way of doing it) or moving a flap to allow the warm air already coming off that radiator to mix in with the

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 37 cold air from outside.It's all these combinations and permutations of plumbing in a water-cooled engine that make it so relatively complex.

FUEL SECTION back to TOC Petrol Petrol is a distilled and refined oil product made up of hydrogen and carbons - a hydrocarbon. A long-chain hydrocarbon to be exact (so don't get it on your skin - its carcinogenic). It's designed to be relatively safe to handle, if you're careful; it doesn't spontaneously combust without extreme provocation.

When you have a petrol fire, it's not the petrol itself that is burning, it's the vapour, and this is the key to fuelling an engine. The carburettor or fuel injectors spray petrol into an air stream. The tiny particles of petrol evaporate into a vapour extremely quickly, and combined in a cloud with the air, it becomes extremely combustible. The smaller the particles from the carburettor jet or fuel injector, the more efficiently the mixture burns.

Detonation, pre-ignition, pinking, pinging and knocking We’ve just said that petrol doesn't spontaneously combust. In fact, it can if the conditions are right, and the conditions are extreme heat and pressure - exactly the conditions you find in the combustion chamber. When this happens, it's called detonation or pre-ignition. Diesel engines rely on this process because they don't have a spark plug in the traditional sense of the word. However in petrol engines, when this happens (also known as dieseling), it's a Very Bad Thing.

Engines are designed so that the fuel-air mix burns at a fixed point in the cycle, and does not explode randomly. Whilst it might look like an explosion, if you could film it on a super high-speed camera, you'd see the mixture actually burns up very quickly rather than exploding.

Detonation, dieseling or pre-ignition are all terms for what happens when the fuel-air mix spontaneously explodes rather than burning. Normally this happens when the mixture is all fouled up, and the engine is running hot. The temperature and pressure build up too quickly in the combustion chamber and before the piston can reach the top of its travel, the mixture explodes.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 38 This explosion tries to counteract the advancing piston and puts an enormous amount of stress on the piston, the cylinder walls and the connecting rod. From the outside of the engine, you'll hear it as a knocking or pinging sound.

The precise sound is very hard to describe because every engine sounds slightly different when it happens. But the best way to describe it is a constant 'toc toc toc' type knocking sound.

Compression ratio The compression ratio of an engine is the measurement of the ratio between the combined volume of a cylinder and a combustion chamber when the piston is at the bottom of its stroke, and the same volume when it's at the top of its stroke.

The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Similarly, the higher the compression ratio, the greater the likelihood of detonation.

Octane ratings - how to stop detonation So you know that a fuel-air mix, given the right conditions, can spontaneously combust. In order to control this property, all petrols have chemicals mixed in with them to control how quickly the fuel burns. This is known as the octane rating of the fuel. The higher the rating, the slower and more controlled the fuel burns. Octane is measured relative to a mixture of isooctane (2,2,4- trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane. The octane value of a fuel used to be controlled by the amount of tetraethyl lead in it, but in the 70s and 80s when it became apparent that lead was pretty harmful, lead-free petrol appeared and other substances were introduced to control octane instead.

Measuring octane - RON, MON The octane number is actually an imprecise measure of the maximum compression ratio at which a particular fuel can be burned in an

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 39 engine without detonation. There are two numbers - RON (Research Octane Number) and MON (Motor Octane Number). The RON simulates fuel performance under low severity engine operation.

The MON simulates more severe operation that might be incurred at high speed or high load and can be as much as 10 points lower than the RON. In Zimbabwe, what you'll see on the petrol pumps is the RON.

What factors affect detonation? There are many things that can affect how likely an engine is to have detonation problems. The common ones are ambient air temperature, humidity, altitude, your engine's ability to stay cool (ie. the cooling system) and spark timing.

Fortunately, nowadays the engine management system of modern cars can compensate for almost all of these by advancing and retarding the ignition timing. This is where the computer slightly adjusts the point in the ignition cycle at which the spark is generated at the spark plug.

With older engines that used mechanical points to send current to the spark plugs, adjusting the timing was a manual affair that involved adjusting the distributor cap orientation.

Knock sensors. Most modern cars have knock sensors screwed into the engine at multiple places. These actually detect the vibration or shock caused by detonation (rather than trying to detect the sound) and can signal the engine management system to change the ignition timing to reduce or eliminate the problem.

Octane and altitude The higher the altitude above sea level, the lower the octane requirement. As a general rule of thumb, for every 300m above sea level, the RON value can go down by about 0.5. For example an 85 octane fuel at 1200m above sealevel will have about the same characteristics as an 87 octane fuel on the coast .

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 40 Octane and power It's a common misconception amongst car enthusiasts that higher octane = more power. This is simply not true. Compression ratio Octane 5:1 72 The myth arose because of sportier 6:1 81 requiring higher octane fuels. Without understanding why, people 7:1 87 decided that this was because higher 8:1 92 octane petrol meant higher power. 9:1 96 10:1 100 The reality of the situation is a little 11:1 104 different. Power is limited by the maximum amount of fuel-air mixture that 12:1 108 can be jammed into the combustion chamber.

Because high performance engines operate with high compression ratios, they are more likely to suffer from detonation. To compensate, they need a higher octane fuel to control the burn.

So it is true that sports cars need high octane fuel, but it's not because the octane rating is somehow giving more power. It's required because the engine develops more power because of its design.

There is a direct correlation between the compression ratio of an engine and its fuel octane requirements.

The table on the left is a rough guide to octane values per engine compression ratio for a carburettor engine without engine management. For modern fuel-injected cars with advanced engine management systems, these values are lowered by about 5 to 7 points.

The exception to prove the rule. Nowadays, higher octane fuel might actually give you more power but not because of the octane rating itself. Some petrol companies use a denser blend for the higher octane products. Denser blends mean higher energy density per volume (measured in Megajoules per litre - MJ/L). For example:

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 41 BP Regular: 32.53MJ/L BP Premium: 33.08MJ/L BP Ultimate: 33.28MJ/L

Do these variations in energy density mean you'll get more power out of your engine from premium blends? Yes, but not in a linear fashion - ie. if the premium product has 5% more energy density than the basic product, you won't get 5% more power out of your engine, simply because of the inefficiencies of internal combustion and thermodynamic considerations.

Octane and petrol mileage Here's a good question: can octane affect petrol mileage? The short answer is absolutely, yes it can, but not for the reasons you might think. The octane value of a fuel itself has nothing to do with how much potential energy the fuel has, or how cleanly or efficiently it burns. All it does is control the burn.

However, if you're running with a petrol that isn't the octane rating recommended for your car, you could lose petrol mileage. Why? Let’s say your manufacturer’s handbook recommends that you run 87 octane fuel in your car but you fill it with 85 instead, trying to save some money on filling up. Your car will still work just fine because the engine management system will be detecting knock and retarding the ignition timing to compensate. And that's the key.

By changing the ignition timing, you could be losing efficiency in the engine, which could translate into worse petrol mileage.

Doing the maths, you can figure out that by skimping on the price during fill-up, you may save a little money right there and then, but it costs in the long term because you're going to be filling up more often to do the same mileage.

Generally, you should do what the handbook tells you. After all, it's in the manufacturer’s interests that you get the most performance out of your car that you can.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 42 Octane boosters In some extreme cases, the highest octane fuel available might not solve a knocking or detonation problem. That's normally a symptom of a deeper problem in the engine involving carbon deposits on the cylinder heads, bad spark timing, faulty engine management systems or similar.

In these cases, some people choose to add octane booster to their petrol. Basically you fill the tank as normal, then put in a measured amount of octane booster and it further raises the octane level in an attempt to stop the detonation.

One of the disadvantages of this is that it can make the engine harder to start from cold, because the octane booster has made the fuel so much less volatile that it's hard to get it to ignite on the first couple of strokes.

Lead Replacement Petrol (LRP) and valve seats Whilst LRP solved the problem of lower octane unleaded petrol, it introduced a new problem. The lead in leaded petrol also had a secondary function and that was to lubricate the valve seats - the top of the engine block where the valves "park" when not being opened by the cams.

With the advent of LRP, detonation went away but the chemicals used to increase octane didn't have any lubricating function. Some older engines started to suffer from increased wear to the valve seats, to the point where the valves could no longer properly close and seal the intake and exhaust ports.

Fuel filters - without them, all this means nothing Without fuel filters, none of this information on petrol is worth anything. Why? In an ideal world,

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 43 every time you fill your tank, the petrol would come from brand new underground tanks, through brand new hoses and nozzles, down a pristine filler tube into a brand new gas tank.

However, in the real world, that simply isn't the case. Tiny bits of metal flake off components. Things rust. Grit and grime gets into the fuel through many different sources.

For the most part, this sediment settles at the bottom of the underground tanks in a petrol station, and at the bottom of the petrol tank in your car. If you're unlucky enough to fill up just after the petrol station has received a load of fuel from a tanker though, all that sediment will be mixed into the petrol, and you'll get a petrol- sediment mix in your petrol tank. Similarly, if you insist on running your petrol tank down to the 'E' mark on the fuel gauge, you'll be sucking up petrol-sediment mix from the bottom of your own tank. It's a good job then that the engineers decided to put in-line fuel filters in your car. These are relatively simple little devices that come in two basic types.

Carburettor engine fuel filters. These are the plastic in-line fuel filters. They look like a little plastic container with a wavy yellow pad in them. They're typically designed to have the fuel sucked through them via a mechanical crank-driven up near the carburettor. In some tuner vehicles you'll find this has been replaced with a little aluminium filter, usually anodised in a nice colour – which unfortunately makes it nearly impossible to find!

Fuel injection filters. These are the metal canister-type fuel filters. They're designed to have the fuel pushed through them by an electric high-pressure fuel pump, and so the pressure in the fuel line is much higher. This is why they're made of metal. Internally, the filter material is normally finer too.

Why filter the fuel? Won't the debris just burn? Generally speaking, unless it's metal filings, then yes, most debris that you'd find in a fuel system would burn during combustion - but that's not the problem. The problem is getting the fuel into the engine in the

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 44 first place. Earlier, you learned about carburettors and fuel injectors. The one thing common to both is the tiny hole at the end of the line where the fuel is finally atomised into the air. A good sized grain of sand would block that tiny hole and once that happens, it doesn't matter how clever your engine is, it won't be getting any petrol.

That is why you have to filter fuel - to keep particulates from clogging up areas of the fuel system vital to its operation.

Most manufacturers will tell you that fuel filters are sealed-for-life, or life-time-of-the-car items. But, in normal operating conditions, in 'first- world' countries, you should change your fuel filter every 75,000 miles (120,000km) or so. If you're doing a lot of driving on dusty roads, your fuel filter might need changing as much as every 5,000 miles (8,000km). If most or some of your petrol comes from a rusty metal jerry can, you might have to change your fuel filter even more often.

Why change the filter? The job of an in-line fuel filter is to filter out sediment and particulates in the petrol that might otherwise cause problems further down the line in the engine. If you think about it, the average car probably has 40 to 50 litres of petrol going through the fuel filter every week.

It stands to reason that eventually the filter is going to become clogged with debris. Once your filter gets clogged, you start to get all sorts of follow-on problems. In carburettor cars, you'll get sporadic and weak fuel supply which will lead to a stuttering engine, or an engine that seems to have no power under acceleration.

In a fuel injection system where the fuel line pressures are much greater, a clogged filter can lead to a burned out petrol pump or a blown fuel line connection on top of the fuel starvation problems.

Where is my fuel filter? Locating the fuel filter on any vehicle can be a real challenge. The filter can literally be anywhere in between the tank and the engine. For carburettor engines it's most likely to be in the engine bay, probably within 50cm of where the fuel line comes up from under the car, and clipped to some other tube or cable.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 45 For injection filters, it's most likely to be attached to the or a suspension component underneath the car at the back axle, close to the fuel pump and petrol tank.

The 'sock' filter More often than not, there will be a mesh 'sock' on the pickup tube inside the petrol tank itself. This is a much trickier filter to change as it's a sort of pre-filter to catch the really large debris. For the most part, these mesh filters don't block easily - anything sucked up against them will normally wash off with the natural movement of the petrol in the tank.

The carburettor internal filter Some carburettors have a last line of defence in the form of a metal gauze filter just inside the fuel intake. If you take the fuel line off a carburettor and peer inside, that's the most likely place for this to be. It's worth knowing about the internal filter because if you go to all the trouble of changing your other in-line filters and still have a fuel starvation problem, it could be this last little filter that's blocked.

ENGINE OIL SECTION back to ToC How much do you value the engine in your car? The life of your engine depends in no small part on the quality of the oil you put in it - oil is its lifeblood.

What does my oil actually do? Your engine oil does many things. Primarily it stops all the metal surfaces in your engine from grinding together and tearing themselves apart from friction, but it also transfers heat away from the combustion cycle. Engine oil must also be able to hold in suspension all the nasty by-products of combustion such as silica (silicon oxide) and acids. Finally, engine oil minimises the exposure to oxygen and thus oxidation at higher temperatures. It does all of these things under tremendous heat and pressure.

What do the numbers around the 'W' mean? For example 5W40? As oils heat up, they generally get thinner. Single grade oils get too thin when hot for most modern engines which is where multigrade oil comes

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 46 in. The idea is simple - use science and physics to prevent the base oil from getting as thin as it would normally do when it gets hot. The number before the 'W' is the 'cold' viscosity rating of the oil, and the number after the 'W' is the 'hot' viscosity rating. So a 5W40 oil is one which behaves like a 5-rated single grade oil when cold, but doesn't thin any more than a 40-rated single grade oil when hot. The lower the 'winter' number (hence the 'W'), the easier the engine will turn over when starting in cold climates.

A quick guide to the different grades of oil

Fully Characteristics Synthetic Fuel economy savings Enhances engine performance and power 0W-30 Ensures engine is protected from wear and deposit build-up 0W-40 Ensures good cold starting and quick circulation in freezing 5W-40 temperatures Gets to moving parts of the engine quickly Semi- Characteristics synthetic Better protection 5W-30 Good protection within the first 10 minutes after starting out 10W-40 Roughly three times better at reducing engine wear 15W-40 Increased oil change intervals - don't need to change it quite so often Mineral Characteristics 10W-40 Basic protection for a variety of engines 15W-40 Oil needs to be changed more often

Mineral or synthetic? Mineral oils are based on oil that comes from Mother Earth, and which has been refined. Synthetic oils are entirely artificial and are made in laboratories.

The only other type is semi-synthetic, sometimes called premium, which is a blend of the two. It is safe to mix the different types, but it's wiser to switch completely to a new type rather than mixing.

Synthetics Despite their name, most synthetic derived motor oils (ie Mobil 1, Castrol Formula RS etc) are actually derived from mineral oils - they are mostly Polyalphaolifins and these come from the purest part of the mineral oil refraction process, the gas. PAO oils will mix with normal

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 47 mineral oils which means that synthetic oil can be mixed with mineral oil, or mineral with synthetic, without the car engine seizing up.

These bases are fairly stable; they are 'less likely to react adversely with other compounds'. They tend not to contain reactive carbon atoms for this reason. Reactive carbon has a tendency to combine with oxygen creating an acid. (As you can imagine, in an oil this would be A Bad Thing.) They also have high viscosity indices and high temperature oxidative stability. Typically a small amount of diester synthetic (a compound containing two ester groups) is added to counteract seal swell too. These diesters act as a detergent and will attack carbon residuals. So think of synthetic oils as custom-built oils. They're designed to do the job efficiently but without any of the disadvantages that can accompany mineral based oils.

Pure synthetics Pure synthetic oils (polyalkyleneglycol) are the types used almost exclusively within the industrial sector in polyglycol gearbox oils for heavily loaded gearboxes. They are made by breaking apart the molecules that make up a variety of substances, like vegetable and animal oils, and then recombining the individual atoms that make up those molecules to build new, synthetic molecules. This process allows the chemists to "fine tune" the molecules as they build them. However, Polyglycols don't mix with normal mineral oils.

Flushing oils These are special compound oils that are very, very thin. They almost have the consistency of tap water both when cold and hot. Typically they are 0W/20 oils. Don't ever drive with these oils in your engine - it won't last. Their purpose is for cleaning out all the deposits which build up inside an engine. Note: Some hybrid vehicles now require 0W20, so if you're a hybrid driver, check your owner's manual.

Do I need a flushing oil? Unless there's something seriously wrong with your engine, you really ought never to need a flushing oil. Even if you're changing from a mineral oil to a synthetic oil, you probably don't need to flush the engine first.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 48 If you do decide to do an oil flush, first drain your engine of all its oil, but leave the old in place. Next, fill it up with flushing oil and run it at a fast idle for about 20 minutes. Finally, drain all the oil off, replace the oil filter, refill with a good synthetic oil and your engine will be clean.

Engine oil categories

Diesel Engines Petrol Engines Category Status Service Category Status Service Introduced in 2006 for high-speed four-stroke engines. Designed to meet 2007 on-highway exhaust emission standards. CJ-4 oils are compounded for use in all applications with diesel fuels ranging in sulphur content up to 500ppm CJ-4 Current (0.05% by weight). CJ-4 oils are

effective at sustaining emission control system durability where particulate filters and other advanced after-treatment systems are used. CJ-4 oils exceed the performance criteria of CF-4, CG-4, CH-4 and CI-4. Introduced in 2002 for high-speed For all four-stroke engines. Designed to automotive meet 2004 exhaust emission engines standards implemented in 2002. CI- 4 oils are formulated to sustain presently in use. SN Current CI-4 Current engine durability where exhaust gas Introduced in the recirculation (EGR) is used and are API service intended for use with diesel fuels symbol in ranging in sulphur content up to November 2010 0.5% weight. Can be used in place of CD, CE, CF-4, CG-4 and CH-4 For all automotive Introduced in 1998 for high-speed engines four-stroke engines. CH-4 oils are specifically designed for use with presently in use. SM Current CH-4 Current diesel fuels ranging in sulphur Introduced in the content up to 0.5% weight. Can be API service used in place of CD, CE, CF-4 and symbol in CG-4. November 2004 Introduced in 1995 for high-speed For all four-stroke engines. CG-4 oils are automotive Still specifically designed for use with engines diesel fuels ranging in sulphur current SL presently in use. CG-4 Current content less than 0.5% weight. CG-4 nearly Introduced in the oil needs to be used for engines obsolete API service meeting 1994 emission standards. symbol in 1998 Can be used in place of CD, CE and CF-4. For all automotive Still engines Introduced in 1990 for high-speed current four-stroke naturally aspirated and SJ presently in use. CF-4 Current nearly turbo engines. Can be used in place Introduced in the obsolete of CD and CE. API service symbol in 1996

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 49

For model year Introduced in 1994 for severe duty, SH Obsolete 1996 and older CF-2 Current two stroke motorcycle engines. Can engines. be used in place of CD-II. Introduced in 1994 for off-road, For model year indirect-injected and other diesel SG Obsolete 1993 and older CF Current engines including those using fuel engines. over0.5% weight sulphur. Can be used in place of CD.

Engine oil grades The API/ACEA ratings only refer to an oil's quality. For grade, you need to look at the SAE (Society of Automotive Engineers) ratings. These describe the oil's function and viscosity standard. Viscosity means the substance and clinging properties of the lubricant. When cold, oil can become like treacle so it is important that any lube is kept as thin as possible. Its cold performance is denoted by the letter 'W', meaning 'winter'. At the other end of the scale, a scorching hot oil can be as thin as water and about as useful too. So it needs to be as thick as possible when warm. Thin when cold but thick when warm? That's where MultiGrade oil comes in. For many years, 20W/50 was the most popular oil. But as engines progressed and tolerances decreased, a lighter, thinner oil was required, especially when cold. Thus 15W/50, 15W/40 and even 15W/30 oils are now commonplace.

How often should I change my oil? You can never change your engine oil too frequently. The more you do it, the longer the engine will last. However, there is a wide range of opinion about exactly when you should change your oil. Some say every 5,000km; some say every 1,000km.

The fact is that large quantities of water are produced by the normal combustion process and, depending on engine wear, some of it gets into the crank case. If you have a good crank case breathing system, the water is removed quickly, but even so, in cold weather a lot of condensation will take place. This is bad enough in itself, since water adversely affects the lubrication process, but even worse, that water dissolves any nitrates formed during the combustion process. You then have a mixture of Nitric (HNO3) and Nitrous (HNO2) acid circulating round your engine! So not only do you suffer a high rate of wear at start-up and when the engine is cold, you suffer a high rate of subsequent corrosion during normal running or even when stationary.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 50 The optimum time for changing oil ought to be related to a number of factors, of which distance travelled is probably one of the least important in most cases. Here is a selection in rough order of importance:

1. Number of cold starts (more condensation in a cold engine) 2. Ambient temperature (how long before warm enough to stop serious condensation) 3. Effectiveness of crank case scavenging (more details in the following pages) 4. State of wear of the engine (piston blow-by multiplies the problem) 5. Accuracy of carburation during warm-up period (extra deposits produced) 6. Distance travelled

Maintenance minders - when the car tells you when to change the oil A lot of cars nowadays come with maintenance minders - inbuilt systems designed to tell you when to change the oil rather than leaving it to guesswork. First generation systems were nothing more than mileage counters. Now they're more involved. The system typically monitors driving style (in terms of how long the throttle is open for any given duration of driving), air intake and external temperatures, coolant temperatures and variations and engine timing (determined by load on the engine and octane of fuel).

Each manufacturer works on a formula that can take in any or all of these factors (and probably more) to determine how fast an average oil will be ageing in your engine. When you get to the point where the system decides your time is up, a light will come on the dash - typically "Maint Reqd" or "Service Reqd" (Note - this is NOT the "check engine" light).

What else happens when I change the oil? Engines pump about 10,000 litres of air for every litre of fuel consumed, and along with all that air, they suck in plenty of dirt and grit. A good air filter will stop everything bigger than a micron in diameter - everything

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 51 smaller mostly just floats around harmlessly in the 0.001 inch mm minimum thickness oil films that separate all the moving parts. Despite all of this, there will always be submicron particles that get in and there will be places in the engines oil-ways where they will gather. Every time you empty the oil from your sump, you're also draining this fine grit with it.

Checking the oil in your engine, and topping up When checking the level of oil in the engine, the car should be on a level surface, and should be relatively cold. If you insist in keeping the crankcase topped off completely, and check the dipstick just after shutting down the engine, you will get an erroneous reading because a quantity of oil (usually about half a litre) is still confined in the oil-ways and passages (galleries) of the engine, and takes some time to drain back into the crankcase. (On the image, the blue areas are where oil is likely to still be running back down to the sump). On seeing what appears to be an abnormally low level on the dipstick, these people then add more oil to the oil filler at the top of the engine. The oil-ways and passages all empty, and suddenly the engine becomes over-filled with oil, going way above the 'MAX' mark on the dipstick.

What happens when an engine is overfilled with oil? You topped up the engine when it was warm after getting a faulty dipstick reading, or you put too much oil in when you changed it yourself. The problem with this is that the next time the engine is run, the windage in the crankcase and other pressures generated by the oil pump, etc. place a great strain on the seal on the rear .

Eventually, often much sooner than you might expect, the rear main bearing seal ruptures, and the engine becomes a 'leaker'. If you've got a manual gearbox, this means one thing: this oil goes right onto the flywheel and the face of the clutch disc.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 52 A lubricated clutch is A Bad Thing. If this still goes unnoticed, the front seal is the next to go, and the engine then starts to spray oil in all directions. As well as smothering the clutch with oil from the rear, the oil now coming from the front leak will be distributed about the engine bay as it hits the front pulley, often propelling it out as far as the brake discs. As you can see from the diagram, the correct oil level is really close to the rotating crank.

Overfilling will mean the crank dips into the oil and churns it into a froth. Froth is good on certain types of coffee but not good in an engine. The mixture of aerated oil will be forced into the bearings. Air is not a lubricant, so bearing damage will follow quite rapidly, especially if you are driving on a motorway. You'll know bearing damage when you get it. The engine smells of burning oil and the noise coming from the engine is loud and discordant. In addition, the excess oil gets thrown up into the piston bores where the piston rings have a hard time coping with the excess oil and pressure. It gets into the combustion chamber and some of it will get out into the exhaust system unburned, resulting in a patina of oil all over the platinum surfaces of your . This ruins the engine completely.

What's the best way to check the oil level? If your engine is cold (for example it has been parked overnight) you can check the oil level right away. The oil will have had time to settle back into the sump. Make sure the car is level before you do. If the engine is warm or hot (after you've been driving) then you should wait for 30 minutes or so to let as much oil as possible drain back into the sump. Checking it first thing the next morning is ideal.

Can I use diesel engine oil in my petrol engine? This is an awkward question to answer. Diesel engines run much higher compression ratios than petrol engines and they run a lot hotter, so the oil is formulated to deal with this. Plus they produce a lot more dirt in terms of combustion by-products. Diesel-rated oils typically have more detergents in them to deal with this. It's not unheard of for diesel oils to clean a petrol engine so well that it loses compression. Diesel- rated oils also have an anti-foaming agent in them which is unique to diesel engines, and not needed in petrol engines.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 53

But this is not the whole answer. The above statement is more relevant to commercial diesel engines. Nowadays, almost all passenger car / light commercial oils (including OEM ones designed for both petrol and diesel engines) will carry the ACEA A and B specifications; they are formulated to satisfy the requirements for both types of engine. So just because the oil is labelled "Diesel" doesn't mean it's not suitable for petrol engines - it will more than likely carry an ACEA A3 / OEM petrol spec as well.

However you do need to be a bit careful regarding choosing the right diesel spec - if you have a modern common rail / direct injection diesel, chances are it will require at least an ACEA B4 spec to cope with the higher piston temperatures that can cause piston deposits (and stuck rings). ACEA B4 is fine where B3 is recommended.

Oil filters and filtration It's all very well changing your oil often, but it's not just the oil that helps prevent engine wear. The oil filter does its part too. Minute particles of dirt are the prime cause of engine wear. The tiny particles are abrasive. They vary from road dust that doesn't get filtered out by the air filter, up to actual metal particles - the by-products of the casting scarf from the original engine manufacture, and basic engine wear.

All this dirt is carried around by the oil into the minute parts of your engine, being rammed into the precision clearances between bearings and other moving parts. Once in, they don't come out easily, but tend to stay there, wearing grooves, grinding and messing up your engine. Other debris that causes problems are a by-product of the mere way an engine works - sooty particles from the combustion process can be forced past the piston rings and transported around in the oil too. The soot acts like a sponge and soaks up other oil additives reducing the oil's anti-wear properties, and messing up its viscosity. All this dirt is why oil goes black when it's used. That lovely syrup-like yellow that it is when you put it in is pure oil. The black stuff that comes out at an oil change is the same oil full of contaminants and by-products from wear and tear.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 54

That's where the oil filter comes in. Its job is to catch all the dirt floating around in the oil, and to stop it from recirculating. Most oil filters are the spin-on type. They're shaped like an aluminium can and spin on to a threaded oil feeder poking out of the side of the engine somewhere. They're called 'full-flow' oil filters because they sit in the normal flow of the oil through the engine. Because it sits in-line, it has to be designed not to restrict the flow of oil around the circuit, and thus can only really be effective at stopping the larger particles – those that are about 20 microns in size.

However, the smallest contaminants are in the 10-20micron size range. They pass right through the oil filter and back out into circulation. This is why regular oil changes are a necessity, because these tiny little things can be the most damaging.

TRANSMISSION SECTION back to ToC This section deals with the process of getting the power from your engine to the ground, in order to move your car (or bike) forwards.

Manual gearboxes - what, why and how? From the Fuel & Engine Section you know that the pistons drive the main crank in your engine so that it spins. Idling, it spins around 900rpm. At speed it can be anything up to 7,500rpm. You can't simply connect a set of wheels to the end of the crank because the speed is too high and too variable. You'd stall the engine every time you wanted to stand still. Instead you need to reduce the revolutions of the crank down to a usable value. This is known as gearing down - the mechanical process of using interlocking gears to reduce the number of revolutions of something that is spinning.

How gears work In this case, gears means 'toothed wheel' as opposed to gears as in 'my car has 5 gears'. A gear (or cog, or sprocket) in its most basic form is a flat circular object that has teeth cut into the edge of it. The most basic type of gear is called a spur gear, and it has straight-cut teeth,

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 55 where the angle of the teeth is parallel to the axis of the gear. Wider gears and those that are cut for smoother meshing are often cut with the teeth at an angle, and these are called helical gears.

Because of the angle of cut, helical gear teeth have a much more gradual engagement with each other, and they operate a lot more smoothly and quietly than spur gears. Gearboxes for cars and motorbikes almost always use helical gears because of this. A side effect of helical gears is that if the teeth are cut at the correct angle - 45 degrees - a pair of gears can be meshed together perpendicular to each other.

This is a useful method of changing the direction of movement or thrust in a mechanical system. Another method would be to use bevel gears.

The number of teeth cut into the edge of a gear determines its scalar relative to other gears in a mechanical system. For example, if you mesh together a 20-tooth gear and a 10- tooth gear, then drive the 20-tooth gear for one rotation, it will cause the 10-tooth gear to turn twice.

Gear ratios are calculated by dividing the number of teeth on the output gear by the number of teeth on the input gear. So the gear ratio here is output/input, 10/20 = 1/2 = 1:2. Gear ratios are often simplified to represent the number of times the output gear has to turn once. In this example, 1:2 is 0.5:1 - "point five to one". This means the input gear has to spin half a revolution to drive the output gear once. This is known as gearing up.

Gearing down is exactly the same only the input gear is now the one with the least number of teeth. In this case, driving the 10-tooth gear as the input gear gives us output/input of 20/10 = 2/1 = 2:1 - "two to one".

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 56 This means the input gear has to spin twice to drive the output gear once.

By meshing many gears together of different sizes, you can create a mechanical system to gear up or gear down the number of rotations very quickly. As a final example, imagine an input gear with 10 teeth, a secondary gear with 20 teeth and a final gear with 30 teeth. From the input gear to the secondary gear, the ratio is 20/10 = 2:1. From the second gear to the final gear, the ratio is 30/20 = 1.5:1. The total gear ratio for this system is (2 * 1.5):1, or 3:1. To turn the output gear once, the input gear has to turn three times.

This also neatly shows how you can do the calculation and miss the middle gear ratios - ultimately you need the ratio of input to output. In this example, the final output is 30 and the original input is 10. 30/10 = 3/1 = 3:1.

Collections of helical gears in a gearbox are what give the gearing down of the speed of the engine crank to the final speed of the output shaft from the gearbox. The table below shows some example gear ratios for a 5-speed manual gearbox:

RPM of gearbox output shaft when the Gear Ratio engine is at 3000rpm 1st 3.166:1 947 2nd 1.882:1 1594 3rd 1.296:1 2314 4th 0.972:1 3086 5th 0.738:1 4065

Final drive - calculating speed from gearbox ratios. It's important to note that in almost all vehicles there is also a final reduction gear. This is also called a final drive or a rear- or front-axle gear reduction and it's done in the differential with a small pinion gear and a large ring gear. In the example above, it is 4.444:1. This is the final reduction from the output shaft of the gearbox to the drive shafts coming out of the differential to the wheels. So using the example above, in 5th gear, at 3000rpm, the gearbox output shaft spins at 4065rpm. This goes

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 57 through a 4.444:1 reduction in the differential to give a wheel driveshaft rotation of 914rpm.

Assume that this vehicle has a wheel and tyre combo of 205/55R16 giving a circumference of 1.985m or 6.512ft. Each minute, the wheel spins 914 times meaning it moves the car (914 x 6.512ft) = 5951ft along the ground, or 1.127 miles. In an hour, that's (60minutes x 1.127miles) = 67.62. In other words, knowing the gearbox ratios and tyre sizes, you can calculate that at 3000rpm, this car will be doing 67mph in 5th gear.

Making gears work together to make a gearbox If you look at the image here you'll see all the internals of a generic gearbox. You can see the helical gears meshing with each other. The lower shaft in this image is called the lay-shaft - it's the one connected to the clutch - the one driven directly by the engine. The output shaft is the upper shaft in this image. To the uneducated eye, this looks like a mechanical nightmare. Once you’ve finished with this section, you'll be able to look at this image and say with some authority, "Ah yes, that's a 5-speed gearbox".

So how can you tell? Firstly, look at the output shaft. You can see 5 helical gears and 3 sets of selector forks. At the most basic level, that tells you this is a 5-speed box (note that my example has no reverse

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 58 gear). But how does it work? It's actually a lot simpler than you might think.

With the clutch engaged (see the section on clutches below), the lay- shaft is always turning. All the helical gears on the lay-shaft are permanently attached to it so they all turn at the same rate.

They mesh with a series of gears on the output shaft that are mounted on sliprings so they actually spin around the output shaft without turning it.

Look closely at the selector forks; you'll see they are slipped around a series of collars with teeth on the inside. Those are the dog gears and the teeth are the dog teeth. The dog gears are mounted to the output shaft on a splined section which allows them to slide back and forth. When you move the gear stick, a series of mechanical pushrod connections move the various selector forks, sliding the dog gears back and forth.

The image to the left shows a close-up of the area between third and fourth gear. When the gearstick is moved to select fourth gear, the selector fork slides backwards. This slides the dog gear backwards on the splined shaft and the dog teeth engage with the teeth on the front of the helical fourth gear. This locks it to the dog gear which itself is locked to the output shaft with the splines. When the clutch is let out and the engine drives the layshaft, all the gears turn as before but now the second helical gear is locked to the output shaft and you’re in fourth gear.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 59 Grinding gears. In the above example, to engage fourth gear, the dog gear is disengaged from the third helical gear and slides backwards to engage with the fourth helical gear. This is why you need a clutch and it's also the cause of the grinding noise from a gearbox when someone does a bad gearchange. The common misconception is that this grinding noise is the teeth of the gears grinding together. It isn't. Rather it's the sound of the teeth on the dog gears skipping across the dog teeth of the helical output gears and not managing to engage properly. This typically happens when the clutch is let out too soon and the gearbox is attempting to engage at the same time as it's trying to drive. In older cars, it's the reason you needed to do something called double- clutching.

Double-clutching, or double-de-clutching (it can be called both) was a process that needed to happen on older gearboxes to avoid grinding the gears. First, you'd press the clutch to take the pressure off the dog teeth and allow the gear selector forks and dog gears to slide into neutral, away from the engaged helical gear. With the clutch pedal released, you'd 'blip' the engine to bring the revs up to the speed needed to engage the next gear, clutch-in and move the gear stick to slide the selector forks and dog gear to engage with the next helical gear.

The synchromesh - why you don't need to double- clutch

Synchros, synchro gears and synchromeshes - they're all basically the same thing. A synchro is a device that allows the dog gear to come to

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 60 a speed matching the helical gear before the dog teeth attempt to engage. In this way, you don't need to 'blip' the throttle and double- clutch to change gears because the synchro does the job of matching the speeds of the various gearbox components for you. Here is a cutaway part of an example gearbox. The centre cone-shaped area is the syncho collar. It's attached to the red dog gear and slides with it. As it approaches the helical gear, it makes friction contact with the conical hole.

The more contact it makes, the more the speed of the output shaft and free-spinning helical gear are equalised before the teeth engage. If the car is moving, the output shaft is always turning (because ultimately it is connected to the wheels). The lay-shaft is usually connected to the engine, but it is free-spinning once the clutch has been operated. Because the gears are meshed all the time, the synchro brings the lay- shaft to the right speed for the dog gear to mesh. This means that the lay-shaft is now spinning at a different speed to the engine.

Then the clutch gently equalises the speed of the engine and the lay- shaft, either bringing the engine to the same speed as the lay-shaft or vice versa depending on engine torque and vehicle speed.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 61 What about reverse? Reverse gear is normally an extension of everything you've learned above but with one extra gear involved. Typically, there will be three gears that mesh together at one point in the gearbox instead of the customary two. There will be a gear each on the lay-shaft and output shaft, but there will be a small gear in between them called the idler gear. The inclusion of this extra mini gear causes the last helical gear on the output shaft to spin in the opposite direction to all the others. The principle of engaging reverse is the same as for any other gear - a dog gear is slid into place with a selector fork. Because the reverse gear is spinning in the opposite direction, when you let the clutch out, the gearbox output shaft spins the other way - in reverse.

The image shows the same gearbox as above modified to include a reverse gear.

Crash gearboxes or dog boxes It's worth mentioning what goes on in racing gearboxes. These are also known as crash boxes, or dog boxes, and use straight-cut gears instead of helical gears. Straight-cut gears have less surface area where the gears contact each other, which means less friction, which means less loss of power – which is why people who make racing boxes like to use them.

Normally, straight-cut gears are mostly submerged in oil rather than relying on it sloshing around like it does in a normal gearbox. So the extra noise that is generated is reduced to a (pleasing?) whine by the sound-deadening effects of the oil.

Normal synchro gearboxes run at full engine speed as the clutch directly connects the input shaft to the engine crank.

Dog boxes run at a half to a third the speed of the engine because there is a step-down gear before the gearbox. The dog gears in a dog box also have fewer teeth on them than those in a synchro box and the teeth are spaced further apart. So rather than having an exact dog-

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 62 tooth to dog-hole match, the dog teeth can have as much as 60° "free space" between them. This means that instead of needing an exact 1- to-1 match to get them to engage, you have up to 1/6th of a rotation to get the dog teeth pressed together before they touch each other and engage. The picture above shows the difference between synchro dog gears and crash box dog gears.

So the combination of less, but larger dog teeth spaced further apart, and a slower spinning gearbox, allegedly make for an easier-to-engage crash box. In reality, it's still quite difficult to engage a crash box because you need exactly the right rpm for each gear or you'll just end up grinding the dog teeth together or having them bounce over each other. That results in metal filings in your transmission fluid, which ultimately results in an expensive gearbox rebuild.

But it is more mechanically reliable - it's stronger and able to deal with a lot more power and torque which is why it's used in racing.

Before the gearbox - the clutch There's a second item in your transmission that you need to understand - the clutch. The clutch is what enables you to change gears, and sit at traffic lights without stopping the engine.

You need a clutch because your engine is running all the time which means the crank is spinning all the time. You need to disconnect this constantly-spinning crank from the gearbox, both to allow you to stand still as well as to allow you to change gears. The clutch is composed of three basic elements; the flywheel, the pressure plate and the clutch

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 63 plate(s). The flywheel is attached to the end of the main crank and the clutch plates are attached to the gearbox lay-shaft using a spline.

In the diagram, the clutch cover is bolted to the flywheel so it turns with the flywheel. The diaphragm springs are connected to the inside of the clutch cover with a bolt/pivot arrangement that allows them to pivot about the attachment bolt. The ends of the diaphragm springs are hooked under the lip of the pressure plate. So as the engine turns, the flywheel, clutch cover, diaphragm springs and pressure plate are all spinning together.

The clutch pedal is connected either mechanically or hydraulically to a fork mechanism which loops around the throw-out bearing. When you press on the clutch, the fork pushes on the throw-out bearing and it slides along the lay-shaft putting pressure on the innermost edges of the diaphragm springs. These in turn pivot on their pivot points against the inside of the clutch cover, pulling the pressure plate away from the back of the clutch plates. This release of pressure allows the clutch plates to disengage from the flywheel. The flywheel keeps spinning on the end of the engine crank but it no longer drives the gearbox because the clutch plates aren't pressed up against it.

As you start to release the clutch pedal, pressure is released on the throw-out bearing and the diaphragm springs begin to push the pressure plate back against the back of the clutch plates, in turn pushing them against the flywheel again. Springs inside the clutch plate absorb the initial shock of the clutch touching the flywheel and as you take your foot off the clutch pedal completely, the clutch is firmly pressed against it. The friction material on the clutch plate is what grips the back of the flywheel and causes the input shaft of the gearbox to spin at the same speed.

Burning your clutch You might have heard people using the term 'burning your clutch'. This is when you hold the clutch pedal in a position such that the clutch plate is not totally engaged against the back of the flywheel. At this point, the flywheel is spinning and brushing past the friction material which heats it up in much the same way as brake pads heat up when pressed against a spinning brake rotor (see the Brake Section). Do this for long enough and you'll smell it because you're burning off the friction material. This can also happen unintentionally if you rest your foot on

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 64 the clutch pedal in the course of normal driving. That slight pressure can be enough to release the diaphragm spring enough for the clutch to lose grip occasionally and burn.

A slipping clutch The other term you might have heard is a 'slipping clutch'. This is a clutch that has a mechanical problem. Either the diaphragm spring has weakened and can't apply enough pressure, or more likely the friction material is wearing down on the clutch plates. In either case, the clutch is not properly engaging against the flywheel and under heavy load, like accelerating in a high gear or up a hill, the clutch will disengage slightly and spin at a different rate to the flywheel. You'll feel this as a loss of power, or you'll see it as the revs in the engine go up but you don't accelerate. Do this for long enough and you'll end up with the above - a burned out clutch.

Motorcycle 'basket' clutches

It's worth spending a moment here to talk about basket clutches as found on some Yamaha motorbikes. Even though the basic principle is the same (sandwiching friction-bearing clutch plates against a flywheel), the design is totally different. If nothing else, a quick description of basket clutches will show you that there's more than one way to decouple a spinning crank from a gearbox.

Basket clutches need to be compact to fit in a motorbike frame so they

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 65 can't be very deep. They also need to be readily accessible for mechanics to be able to service them with the minimum amount of fuss, something that's almost impossible with regular car clutches. A basket clutch has a splined clutch boss bolted to the shaft coming from the engine crank with strong springs. Metal pressure plates slide on to this shaft, in alternating sequence with friction material clutch plates.

The clutch plates are splined around the outside edge, where they fit into slots in an outer basket - the clutch housing. The clutch housing is bolted on to the lay-shaft which runs back through the middle of the whole mechanism and into gearbox.

In operation, a basket clutch is simple. A throw-out bearing slides around the outside of the lay-shaft and when you pull the clutch lever, the throw-out bearing pushes against the clutch boss. The clutch boss compresses the clutch springs and removes pressure from the whole assembly. The friction plates now spin freely in between the pressure plates. When you let the clutch out, the springs push the clutch boss in again and it re-asserts the pressure on the system, crushing the friction and pressure plates together so they grip. And there you have a second type of clutch.

Automatic gearboxes Automatic gearboxes are a totally different thing. For a start they don't have a clutch pedal. For that matter they don't have a clutch at all; they have a torque converter. If you took an automatic gearbox apart (but please don't), you'd see an enormous collection of mechanical parts all jammed into an impossibly small space. The most important part would be the planetary gear-set. In a manual gearbox, the dog gears lock and unlock different sets of helical gears to the output shaft in order to give the various gear ratios. In an automatic gearbox, the planetary gear-set produces all the different gear ratios in one go and with only one set of gears. An automatic gearbox is very much more complicated than a manual gearbox.

How planetary gear-sets work Any planetary gear-set has three main components: the sun gear, the planet gears (and their carrier) and the ring gear. Any one of these three components can be locked in place, but more importantly, any one can be the input or the output drive. Locking any two of them at the

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 66 same time will always produce a 1:1 gear ratio. So how does that work? One set of gears for every ratio you need? Imagine a planetary gear-set with a ring gear that has 75 teeth and a sun gear that has 25 teeth. The following table shows how sending the input to one set of gear and locking another set can give a wide variety of gear ratios.

Locked Resulting Input Output Calculation gears ratio Planet Sun Ring 1+(Ring/Sun) 4:1 Carrier Planet Ring Sun 1/(1+(Sun/Ring)) 0.75:1 Carrier Planet -3:1 (ie. Sun Ring -Ring/Sun Carrier reverse)

So that table basically has one reverse and two forward gears. If you need more gears, add more planetary gear-sets with different numbers of teeth and link them together. Make the output of one become the input of another and you can start to multiply up the number of gears available to you. The image here shows an example planetary gear-set with the planet carrier in cutaway.

Compound planetary gear-sets In reality, automatic gearboxes typically use one or more compound planetary gear-sets instead of chaining regular gear-sets together. They look just like a regular

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 67 planetary gear-set from the outside, but inside there are two sun gears and two sets of intermeshing planet gears.

There is still only one ring gear though. With a single compound gear- set, the number of ratios available increases to 4 forward ratios and one reverse. The image shows an example compound planetary gear- set again with the planet carrier in cutaway. The planet gears are arranged as inner and outer planets. The inner ones are shorter and only engage the small sun gear and the outer planet gears. They in turn engage the larger sun gear at the bottom and the outermost ring gear.

Another configuration would be to have the two sets of planet gears next to each other but slightly staggered so that only one set meshes with the ring gear. Here is an explanation of the first two gears. Look at the images here.

When first gear is engaged, the smaller sun gear is driven from the torque converter.

The planet carrier tries to spin the opposite direction but because of a one-way clutch system, it locks in place, and forces the ring gear to turn instead.

The ring gear becomes the output from the gearbox in this case and you’re in first gear.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 68

The catch is that because of the design of the compound gear-set, the direction of rotation of the output shaft ought to be opposite to that of the input shaft, but it isn't.

This is because the first set of planet gears engages the second set and it's the second set that turns the ring gear. Doing this reverses the direction of rotation, thus making it now the same as the input shaft.

When second gear is engaged the input is again the small sun gear but this time the ring gear is held in place by a band and the output becomes the planet carrier.

Locking planetary gear-set components You might now be wondering how the clutches and bands mentioned above actually work. Bands are literally that - they're a band wrapped around the outside of the ring gear and when tightened, they lock the ring gear in place.

Bands are actuated by a lever or pivot connected to a small hydraulic piston in the gearbox housing. The image shows how a band might work. The actuator piston actually sits in a small cylinder inside the hydraulic distributor (see later) which is built into the gearbox case. You can see the band wraps around the ring gear. When the piston is pushed down it tightens the band and clamps the ring gear into place, locking it to the gearbox case.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 69 The clutches are a little more complex and are used to perform functions such as locking the sun gears to the turbine or input shaft. Automatic transmission clutches are a lot like the motorbike basket clutches mentioned earlier. They consist of a series of pressure and friction plates with splines on the inside and outside. These are compressed by hydraulic fluid fed through channels in the various shafts to a clutch piston. Clutch springs make sure the clutch piston releases when hydraulic pressure is reduced. The example here shows how a clutch system might work to lock the ring gear to the output shaft.

The automatic gearbox hydraulic system - how it changes gears You've got the idea by now that hydraulics are used a lot in an automatic gearbox. They're used to pressurise the piston plate for the clutches and they're used to move the band-activation pistons up and down. In the past, the routing of the hydraulic fluid in the system was controlled by mechanical shift valves linked to the throttle valve on one side and the governor (see later) on the other. These days, generally speaking, when you move the gear stick, you're doing nothing more than giving an input to the engine management system or engine

control unit (ECU) indicating what gear you'd like to be in. The ECU then looks at engine speed, speed across the ground, current gearbox configuration and position of the gear selector and decides what the best action is. It signals solenoid shift valves inside the hydraulic system to open and close appropriately and the gearbox then changes gears as necessary.

But how does the gearbox know to go up gears when you're speeding up, and down when you're slowing down? There's a device called the

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 70 governor attached to the output shaft of the gearbox. It's a centrifugal sensor connected into the hydraulic circuit. The faster you're going, the faster the governor spins and the more open the valve in it becomes.

That in turn allows the pressure of the hydraulic circuit to rise, which then applies more pressure to different components, pistons and clutch activators and lets the gearbox shift up at the right speeds. Again, in modern cars, all this information is fed through the ECU which also takes another input from a throttle sensor or more usually a vacuum modulator. These devices allow the ECU to know how hard the engine is working - something else that's critical to how the gearbox operates. It's these inputs that can sense the sudden need for more power so that when you press the accelerator to the floor, the gearbox can downshift.

The ECU sees a relatively sedate output shaft speed from the governor but a sudden and dramatic increase in vacuum pressure in the engine intake manifold. This is the key to move the gearbox down a gear to get more power – quickly!

Limiting gear selection. Most gearbox selectors have a '1' and '2' position. When you select one of these positions you're inhibiting the gearbox's ability to pick any gear higher than that. In a mechanical system it locks off certain portions of the hydraulic system physically so the gearbox simply cannot provide hydraulic pressure to the selector components. In a modern electronic gearbox, you're telling the ECU "don't select anything higher than this". The ECU will then never send commands to open the solenoid valves to activate higher gears.

The pump. Obviously, some sort of pressure is needed to make all the hydraulics work. The pressure comes from the hydraulic pump. This is normally located in the cover of the gearbox housing itself and it draws fluid from the gearbox sump to feed the gearbox hydraulic system, the fluid cooler (basically a small radiator) and the torque converter. The pump itself is a typically a rotary displacement pump that uses the difference in pressure between the spinning centre lobe and the outer housing to suck fluid in on one side and expel it on the other.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 71 Parking "P" is the park position on an automatic gear selector. If you've ever engaged park just before you've actually stopped, you'll have heard a clicking sound followed by a thud as the gearbox locks and the car rocks forwards. The mechanism that does this is extremely simple.

It is nothing more than notches on the outside of the clutch housing and a single or pair of spring-loaded catches. The image here shows the basic idea behind the park mechanism in an automatic. When you put the gearbox in 'P' for park, the catches are deployed and they fit into the notches on the outside of the clutch housing. Simple.

Torque converters Just like a manual gearbox, an automatic gearbox needs a method of decoupling the constantly-spinning engine from the gearbox

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 72 components. To do this it uses a torque converter which is a viscous fluid coupling (because it's full of hydraulic fluid). A torque converter consists of three basic elements: the impeller, the turbine and the stator. The impeller is attached to the torque converter housing which itself is attached to the engine flywheel. The impeller is basically a centrifugal pump.

As the flywheel spins, so does the impeller. The vanes take the fluid from the central part of the torque converter and fling it to the outside creating a pumping action. The fluid then circulates around the outer edge of the torque converter and back into the turbine. The turbine is basically the opposite of the impeller - it's like a ship’s propeller in that the fluid passing through it causes it to spin.

The turbine is connected to the input shaft of the gearbox via a splined shaft so as the turbine spins, so does the input shaft to the gearbox. The fluid passes through the turbine from the outside towards the inside. Finally, as the fluid reaches the central core, it passes through the stator which is designed to help redirect the flow into the inner vanes of the impeller. (Without the stator, the whole system would be a lot less efficient.) With this mechanism, the fluid is constantly being circulated.

When the engine is idling, the fluid is pumping around without a lot of force and the amount of torque on the turbine is minimal. As you accelerate, the impeller speeds up and creates larger forces on the turbine which in turn spins more quickly and with more torque. Because it's connected to the input shaft of the gearbox, this feeds more rotational speed and torque into the gearbox and the car starts to move forwards.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 73 It's because of this viscous liquid coupling that automatic gearboxes have a certain amount of 'slop' in them - the engine can rev up and down without the car actually changing speed very much. It's also the reason automatics are less fuel efficient because the torque converter uses up energy from the engine simply in its design by spinning the hydraulic fluid.

The yellow arrow shows the basic circulation path of the fluid inside as it is pumped from the impeller (red) through the turbine (blue) and back through the stator (green). For sportier vehicles or those with specialised needs, some torque converters include a hydraulic clutch.

Once the car is moving and in top gear, the clutch engages and locks the turbine to the impeller. Once that happens, the whole torque converter spins as one and the viscous coupling becomes redundant - effectively the gearbox now behaves like a manual because the engine flywheel is connected directly to the gearbox input shaft. By locking all the components together, it makes the car as fuel efficient as a manual when in top gear because the energy that was being used up in the viscous coupling is no longer required. It also means instantaneous throttle response - you push the accelerator and the car accelerates instantly just as with a manual.

But why is it called a torque converter? Very simply, because it has the ability to multiply the torque from the engine 2 or 3 times in certain conditions. Basically, from a standing start, when the engine is spinning far faster than the gearbox, the whole design allows the torque from the flywheel to be multiplied. As the car gets up to speed, the multiplication factor drops until it becomes 1x once everything is in motion and the impeller and turbine are moving at almost the same speed.

Doing it yourself. You can demonstrate the principle behind a torque converter at home. Get a large bucket or bowl and a cordless drill with a paint-stirrer. Fill the bucket with water and put some bits of paper around the outside of the bucket, floating on the water. Put the paint stirrer in the middle and pull the trigger on the drill. To start with, the paint stirrer is spinning much faster than the water in the bucket, and the bits of paper will barely be moving.

As the water in the bowl begins to speed up its circulation, the bits of paper will being circulating the bucket at speed. Eventually the water in

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 74 the bowl will be circulating at almost the same speed as the paint stirrer is turning. It's that "almost" that shows the inefficiency in a torque converter - the fluid can never spin at exactly the same speed and thus it can never impart the exact same torque and motion into t he turbine.

Now imagine that the bucket or bowl has vanes around the inside of it.

As the water is circulating, it's going to be applying force to those vanes and (given a slippery enough surface) your bucket or bowl will eventually start to spin. The drill and the paint stirrer are the input from the engine and the spinning bucket is the output to the gearbox.

The other way to do this is to take two desk fans, turn one on and point it at the other. Eventually the second fan will start to spin because of the air being forced past it by the first fan. This uses the same principle - but with moving air instead of moving water.

TipTronic® Gearboxes If you've owned a VW or Audi in the last few years it might have come with a TipTronic® gearbox. To you, the driver, it looks like a regular automatic gearbox but with an H-gate for the gearshift. In normal operation, you use the gearbox just like an automatic, putting it in 'D' for Drive and just letting it go about its business. But if you click the gearstick over into the H-gate it becomes a discrete automatic, meaning you can then click it forwards and backwards like a

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 75 sequential gear-change. In this mode you are basically telling the gearbox when you want it to shift rather than allowing it to shift for you. When you click it forwards for example, you're indicating a desire to go up a gear. The ECU looks at the engine speed, road speed, torque and load and if all the planets align, it shifts up by activating the relevant solenoid valves in the automatic hydraulic system.

Most TipTronic® designs do have a certain amount of idiot-proofing though, and if you try to over-rev the engine in first, it will override you and automatically shift up to second to save the engine. These types of gearboxes often have steering-wheel shifters either as buttons or triggers on the steering wheel (like the Mazda MX-5) or paddle- shifters. TipTronic® is actually a design from Porsche and they simply license it to other vendors, typically German manufacturers.

CVT - continuously variable transmission CVTs - continuously variable transmissions - are based on simplicity rather than complexity. Gone is the nightmare of spinning, whirling, intermeshing gears, clutches, clamps, bands, friction plates and so on. Instead, the CVT essentially has three moving parts: two pulleys and a belt.

The first CVTs used rubber composite belts, but the durability and strength of these belts just wasn't suitable for serious car engines. This led to the development of a metal belt which allowed the normally slack side of the belt to actually push, and so was able to deal with higher torque values (up to 450Nm). The modern push-belt is made up of hundreds of individual, specially designed steel elements, which are strung together along 2 high-alloy steel ring packs.

What makes the CVT so attractive to the automotive and motorcycling markets? Apart from the simplicity, it has one extremely sound engineering principle: get the engine to peak torque and keep it there whilst infinitely varying the transmission. That way the engine is always performing at peak capacity. No changing gears, no revving up and down the rev range, and as Nissan so aptly put it - no shift shock.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 76

So how does the CVT work? Simply. Very simply. The most basic CVT has two variable pulleys and either a steel-core rubber pull-belt or a steel alloy push-belt. One pulley is connected to the flywheel and the other to the gearbox output shaft. The belt loops around between the two. On simple scooter-type CVTs, the pulleys change geometry simply by rotational forces - the faster the engine pulley spins, the more it closes up and the faster the output pulley spins, the more it opens out. In automotive applications, the geometry of the pulley is governed by a hydraulic piston connected to the ECU.

The pulley itself is basically a splined shaft with a pair of sliding conical wedges on it (called 'Sheaves'). The closer the wedges are together, the larger the radius 'loop' the belt has to make to get around them. The further they are apart, the smaller the radius 'loop' the belt has to make. If the flywheel pulley has a small radius and the output pulley has a large radius, then the transmission is essentially in low gear.

As the car gets up to speed, the two pulleys are adjusted together so that they present an infinitely changing series of radii to the belt which ends up with the flywheel pulley having the largest radius and the output pulley having the smallest.

Have a look at the pictures on above.

The image on top shows the basic layout of a pulley-based CVT with the two sliding pulleys and the drive belt. This is the equivalent of 'low

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 77 gear' - the drive pulley spins two or three times for each rotation of the output pulley. It's the equivalent of a small gear meshing with a large gear in a regular manual gearbox.

The lower image shows the same system in 'high gear'. The drive pulley has closed up forcing the drive belt to travel a larger radius. At the same time, the output pulley has pulled apart giving a smaller radius. The result is that for each turn of the drive pulley, the output pulley now spins two or three times. It's the equivalent of a large gear meshing with a small gear in a regular manual gearbox. The difference here is that to get from the low gear to the high gear, the infinite adjustment of the position of the pulleys basically means an infinite number of gears with no point where the drive is ever disconnected from the output.

Toroidal CVT (Nissan Extroid) As good as a belt-driven CVT is, the weak link is the belt. If it gets damaged in any way, the transmission becomes useless. Another solution then is the toroidal CVT which is equally simple in operation but has parts which are less prone to wear than the belt-drive type. With a toroidal CVT, both the input and output shafts are sculpted metal discs that face each other. In between are two rollers that free-wheel on their x-axis, making contact with both discs. The position of the rollers is controlled hydraulically and they pivot in their z-axis around a common centre so that wherever they are in their rotation, the rollers always touch the discs. Because the position of contact changes on the discs, the relative rotation of each disc changes. The image shows a toroidal CVT in low gear. The input shaft is on the left.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 78

As it spins, the rollers make contact on the surface of it in the area shaded red. This spins both rollers on their x-axes, and because they both touch the output disc, it is spun in turn. The contact area on the surface of the output disc scribes a much larger circle - again rendered as red. This is the equivalent of a small gear driving a large gear - the gearbox is effectively in low gear.

For a toroidal CVT to increase the output shaft speed, both the rollers

are pivoted slowly about their y-axes.

As they do this, their point of contact on the input and output discs changes in an infinitely smooth, continuous motion.

Effectively, the radius of the path on the input disc gets larger and larger as the radius of the path on the output disc gets smaller and smaller.

This creates an infinite number of gear ratios until 'top gear' is reached when the rollers are in the opposite position to where they started. Now you can see the equivalent of a large gear driving a small gear - the gearbox is effectively in high gear.

This type of infinitely adjustable toroidal CVT can deal with very high torque figures and can be stacked up end-to-end to provide other gearing options.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 79

Differentials With one or two exceptions, every car has a differential.

You need to understand a very simple concept to do with circles.

When you make a car go around a corner, the outer wheels travel further than the inner wheels. Have a look at the diagram here to see an illustration of the concept.

The first thing you'll notice is that the rear wheels take a different path to the front wheels, but the other thing to notice is that because the car's wheels are describing different radius arcs, the further away from the centre-point of the arc, the larger the distance that gets travelled. In car terms, that means the outer wheels need to turn more times than the inner ones every time you go around a corner, because they're describing a larger arc. The brighter ones amongst you will now have figured out that if the outer and inner wheels were joined together with a solid axle, one of them could not turn more times than the other - they'd have to turn at the same rate. That is the crux of the matter. Differentials basically allow two wheels on the same axle to turn at different rates. (As well as allowing the wheels on the same axle to turn at different rates, the differential also acts as the final gear reduction in the driveline.)

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 80 Is there a differential on each axle? That depends. On a two-wheel-drive car, no. Only the driven axle needs a differential. The undriven wheels are not connected to each other so the differential is unnecessary. For four-wheel-drive or all- wheel-drive vehicles, then yes, both the front and rear will have differentials because they are both driven axles. Technically, a differential is a torque-splitter. It splits the input torque two ways to two output shafts, each of which can turn at a different rate. For full-time all- wheel-drive, there is often a third differential in the driveline from the front to the rear of the vehicle, to allow the entire front and rear axles to spin at different speeds to each other.

The difference between the various drive systems is illustrated later in the section on 2WD, 4WD and AWD.

Open differentials We'll deal with open differentials first because they're the easiest to explain, they're the most common, and they supply the same amount of torque to each output. Open differentials have a few essential components, illustrated above. The input pinion gear is the gear that is driven from the drivetrain - typically the output shaft from the transmission. It drives the ring gear which, being larger, is what gives that final gear reduction mentioned above. Attached to the ring gear is the cage, containing two captive pinion gears that are intermeshed with the two output pinion gears, one connected to each axle. The captive pinions are free to rotate how they wish.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 81 As the input pinion spins, it meshes with the ring gear. The ring gear spins, spinning the cage and the two captive pinions. When the vehicle is travelling in a straight line, neither drive pinion is trying to spin any differently from the other, so the captive pinions don't spin and the turning of the ring gear is translated directly to both drive pinions. These are connected to the drive-shafts to the wheels, so effectively, the ring gear spins the wheels at the same speed that it is turning. When the vehicle starts to turn a corner, one of the wheels is going to want to spin more quickly than the other. At this point, the captive pinions come into play, allowing the two drive pinions to spin at slightly different speeds whilst still transmitting torque to them.

You can tell if your vehicle's differential is working properly by jacking the driven axle up off the ground and spinning one wheel. When you do, because the gearbox is stationary, it holds the ring gear solid, the captive pinions spin in opposite directions, and the other wheel on the axle spins the other way around. This also explains why a two-wheel- drive vehicle can get into trouble when one wheel has less friction with the ground than the other. The open differential cannot compensate for this. If one drive pinion is held solid compared to the other, then all the input gets redirected to the drive pinion that has the least resistance.

This is why when you gun a two-wheel-drive car with one wheel in soft mud and the other on the road, the wheel on the mud spins and the wheel on the road doesn't. You don't go anywhere because all the engine power is directed to the wheel with least resistance - the one on the soft mud.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 82

Imagine the same scenario on a four-wheel-drive vehicle that has open differentials on the front and rear. If you're off-roading in such a vehicle and get it into a situation where one front wheel and one rear wheel are off the ground, you're stuck. The differentials will spin the airborne wheels and send no torque to the ones on the ground. That leads us nicely on to the next topic:

Limited-slip differentials Sometimes known by the name "positraction", the simplest form of limited-slip differential is designed to combat the scenario outlined above. Physically there's not a lot of difference in the design of a

limited-slip differential. It still has all the components of an open differential but there are two crucial extra elements. The first is spring pressure plates which are a pair of springs and pressure plates nestled in the cage between the two drive pinions. These push the drive pinions outwards where the second extra element comes into play - clutch packs.

The backside of the drive pinions have friction material on them which presses against clutch plates built into the cage. This means that the clutch is always going to try to behave as if the car was moving in a straight line by attempting to make both output pinions spin at the same speed as the ring gear and cage. However, when a car with a limited- slip differential goes into a corner, there are enough forces at play that the drive pinions begin to slip against the clutch material, thus allowing them to turn at different speeds again. The stiffness of the spring pack

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 83 coupled with the friction of the clutch pack together determine the amount of torque required to overcome the clutch.

So let’s go back to our unfortunate driver stuck with one wheel on soft mud and another on the road. With a limited-slip differential, because of the spring- and clutch-packs, even though one wheel is on the mud, the differential is going to attempt to spin both drive pinions at the same speed. With low engine revs and steady throttle control, the wheel on the road will get enough spin to move the vehicle forwards. If the engine is revved hard though, it can still generate sufficient torque to overcome the clutch pack and once again, only the wheel on the mud will spin. To get around this, it's a good idea to try to pull away in second gear - that gives the limited-slip differential a chance to do its job. The drawing above shows the generic open differential from the previous page modified to be a limited slip differential.

Torsen differentials Torsen differentials are a derivative of open differentials. They derive their name from their function - Torque-Sensing. When the torque going to both outputs is the same, a Torsen differential essentially works just like an open differential. The change comes when the torque going to each output begins to change, for example as a result of a slippery road surface under one wheel. When this happens, what's known as an Invex gear train (inside the differential) begins to bind together.

The Invex gear train is designed with a torque bias ratio in mind that determines the ratio of torque that it can split between the outputs as the gear-train begins to bind together.

A 3:1 Torsen differential, for example, can deliver three times the torque to the output that has more traction. The downside of this is that if one output suddenly ends up with no traction at all, the differential won't be able to supply any torque to the other output. Using the 3:1 example, one output can have up to three times the torque than the other. If one output has zero traction, then three times zero is zero, so the other output also gets no torque.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 84

Torsen differentials are normally used in-line between the front and rear drives for performance all-wheel-drive vehicles, to split the torque between the front and rear axles, rather than the left and right wheels.

How does a Torsen 'sense' torque? The Invex geartrain is essentially a set of helical-cut gears that all mesh together and torque-sensing is not really the right name. The Torsen differential is an entirely mechanical affair with no clutches, hydraulics, actuators or sensors. It doesn't really 'sense' anything. If you look at the rendering on the previous page, you can see the Invex gears mesh with the helical drive pinions. At the ends of the Invex gears are regular-cut gears that mesh with each other. So in this example, looking at the top pair of Invex gears: the left gear meshes its helical-cut part with the helical left drive pinion, and it meshes its regular-cut part with the right Invex gear. That gear in turn meshes its helical-cut part with the right helical drive pinion. It is this interconnectivity that allows the Torsen to work like an open differential when the torque is even, but as a torque- sensing unit when its not.

Where the helical cuts mesh together (shown in close-up in on the right), there's a certain amount of friction inherent in that design. The angle of the helical spiral used to create the gears determines the amount of force required to make them turn. The shallower the pitch of the spiral, the more force required, and hence the more torque required to turn two meshed gears. That's the clever part then - the spiral pitch. The precise spiral pitch angle determines the torque bias ratio.

The whole system works on simple high-school physics. With helical gears, the steeper the pitch of the spiral, the less torque required to make them mesh together.

Locking differentials Locking differentials are another derivative of open differentials but with an electronic, pneumatic or hydraulic actuation system that locks the two drive pinions together as if they were a solid axle. This is for use in serious off-roading, where a vehicle will spend a lot of time with one wheel per axle in the air. By locking the differential, it behaves like a solid axle and both wheels are spun together.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 85 AWD couplings Viscous couplings Viscous coupling aren't really a type of differential but they're worth mentioning because they're used a lot in all-wheel drive vehicles. Lower end AWD vehicles are actually mostly 2-wheel drive vehicles (see the article below for all the differences) until the front wheels begin to slip.

When that happens, they become all-wheel-drive through the use of a viscous coupling. In its most simple form, it's essentially identical to the torque converter found in an automatic gearbox.

Hydraulic clutch couplings Again, this is not really a differential, but another type of device used in AWD cars to engage the rear differential. With these types of coupling, the front and rear differentials drive hydraulic pumps - normally filled with oil. Any difference in the speed of the two pumps causes a pressure imbalance in the system that activates a clutch pack in-line to the rear differential to engage it. So again, when the front wheels spin faster than the rear (meaning slip), the clutch pack is engaged and the rear differential comes into play. These types of coupling typically also have braking and thermal overrides so that if the gearbox oil in the rear differential becomes too hot, or the car is braking, the clutch pack can be overridden and disengaged. Without this, ABS-equipped vehicles would not be able to sense all four wheels correctly under braking.

2WD, 4WD, AWD In the last couple of pages you've now seen a lot of references to 2WD (two-wheel drive), 4WD (four-wheel drive) and AWD (all-wheel drive). Time to explain the differences.

2WD - two-wheel drive This is by far the most common type of drivetrain in any car today. The engine drives the gearbox which sends its output to an open differential either on the front or rear axle, which in turn drives those wheels. If one of the driven wheels comes off the ground, or gets on a slippery surface, the car gets stuck because all the torque is being

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 86 sent to that wheel whilst the other three sit there helpless.

4WD - four-wheel drive Also known as part-time all-wheel drive, this system has an open differential on the front and rear axle and a transfer case on the output from the gearbox. Typically 4WD is normally driving the rear axle with the front axle only coming into play in 4WD mode. The transfer case is the device that splits the torque between the front and rear axles. It typically has some sort of selectable internal differential or viscous coupling to allow the front and rear drives to turn at different speeds if need be. Some trucks and SUVs have a selector with 2H, 4H and 4L on it - it looks like a second gear shift.

This is actually controlling how the front and rear outputs of the transfer case get locked together. In 2H mode (2-wheel drive, high), it essentially disconnects the front output completely and only drives the rear axle. In 4H mode (4-wheel drive, high), it engages the front output via the viscous coupling so that the axles can turn at different speeds, and now sends torque to both open differentials. In 4L mode (4-wheel drive, low) it engages a second set of reduction gears and locks the front and rear axles together so they must spin at the same speed.

This would be bad for on-road driving because it does not allow any difference in speed between the front and rear wheels, so you'd often get dragging and slipping which would make the car essentially unsafe to drive. However, locking everything together like this and reducing the gear ratio makes perfect sense for off-roading, which is why it's an option. However, with open differentials, it's still entirely possible to get stuck with a 4WD vehicle. If you're off-roading and the front-left and rear-right wheels both leave the ground together (for example), then the torque will all be sent to those wheels and they'll spin helplessly in the air. Locking, limited-slip or Torsen differentials solve this but add weight, complexity and cost to the system.

Locking hubs On older 4WD systems, the front wheels could only be engaged to the transfer case by locking hubs. Essentially the transfer

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 87 case was always sending torque to the front driveshaft and had no viscous coupling. To get into 4WD mode, the driver had to stop, get out, and lock the front wheels to the axles so they could be driven.

In newer 4WD systems, the lockable hubs are still present on some models, but are designed more for mechanical sympathy and fuel economy than anything else. With the hubs on locked, the whole front part of the drive system isn't being dragged along for the ride, which causes mechanical wear and a drop in fuel economy.

AWD - all-wheel drive type 1 Finally, all-wheel drive or full-time 4WD. Found mostly on sportier cars, but also on some SUVs, there are two types of AWD, both designed to try to overcome the problems with 4WD. The simplest form has two open differentials - one on each axle - and a viscous coupling between. The engine drives the gearbox which drives two output shafts. One goes to the front open differential and the other goes to the viscous coupling, the output of which is connected to the rear open differential. Under normal conditions, this type of AWD system functions exactly like a 2WD car, driving only the front axle (unlike a 4WD which normally drives the rear axle). The front wheels turn at a certain rate, and the rear wheels are dragged along for the ride. Both halves of the viscous coupling are spinning at the same speed so no torque is sent to the rear axle.

If the front wheels begin to slip and spin, the input to the front of the viscous coupling begins to spin faster than the rear and because of its torque-converter-like design, this causes the rear output to want to speed up. At this point, the drive-train is now transferring torque to the rear axle and the car starts to function in AWD mode. Actually, AWD is a bit of a misnomer at this point, because unless the car has limited-slip differentials front and rear, it's still only really driving two wheels in this mode - the one on the front and the one on the rear axles that have the most traction. That leads us nicely on to.....

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 88

AWD - all-wheel drive type 2 This is the other type of AWD found on rally cars, expensive sports sedans, etc. Very similar to the type 1 AWD, it replaces the viscous coupling with a Torsen differential, and replaces the open differentials front and rear with either Torsen or limited-slip differentials. This is the only true all-wheel-drive system because it will always drive all four wheels. It’s also very expensive and it saps petrol-mileage because of all the extra drag induced in the driveline.

FWD, RWD, FE, ME, RE Not to be confused with the descriptions above, these acronyms determine the engine location and driven axle(s) on a car.

FWD = front-wheel drive. RWD = rear-wheel drive. FE = front engine. ME = mid engine. RE = rear engine.

The position of the engine, being the heaviest part of the car, affects how the car handles. Most vehicles are front-engined, front-wheel drive

(FE-FWD) with the engine, gearbox and differential all clustered together in one place.

BMWs and other higher-end vehicles are front-engined, rear-wheel drive (FE-RWD) with a prop-shaft going from the gearbox and engine at the front to the differential at the rear.

Sports cars like the Toyota MR2 and the McLaren F1 are mid-engined. Putting the engine as close as possible to the middle of the car gives the best possible front-to-rear weight distribution and gives predictable, even handling. Mid-engined cars are

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 89 typically rear-wheel drive (ME-RWD).

Finally, rear-engined vehicles such as most Porsches and the original VW Beetle have the engine, gearbox and differential all clustered at the rear of the car and are typically rear-wheel drive (RE-RWD). The disadvantage of this is that when cornering, with that much weight at the back of the vehicle, it can behave like a pendulum and induce chronic oversteer in corners.

BRAKES SECTION back to ToC Brakes - what do they do?

The simple answer: they slow you down.

The complex answer: brakes are designed to slow down your vehicle but probably not by the means that you think. The common misconception is that brakes squeeze against a drum or disc, and the pressure of the squeezing action is what slows you down. This in fact is only part of the equation. Brakes are essentially a mechanism to change energy types.

When you're travelling at speed, your vehicle has kinetic energy. When you apply the brakes, the pads or shoes that press against the brake drum or rotor convert that energy into thermal energy via friction. The cooling of the brakes dissipates the heat and the vehicle slows down. It's the First Law of Thermodynamics, sometimes known as the law of conservation of energy.

This states that energy cannot be created nor destroyed, it can only be converted from one form to another. In the case of brakes, it is converted from kinetic energy to thermal energy.

Angular force. Because of the

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 90 configuration of the brake pads and rotor in a , the location of the point of contact where the friction is generated also provides a mechanical moment to resist the turning motion of the rotor.

Thermodynamics, and drilled rotors If you ride a motorbike or drive a race car, you're probably familiar with the term brake fade, used to describe what happens to brakes when they get too hot. A good example is coming down a mountain pass using your brakes rather than your engine to slow you down.

As you start to come down the pass, the brakes on your vehicle heat up, slowing you down. But if you keep using them, the rotors or drums stay hot and get no chance to cool off. At some point they can't absorb any more heat so the brake pads heat up instead. In every brake pad there is the friction material that is held together with some sort of resin and once this starts to get too hot, the resin starts to vaporise, forming a gas.

Because the gas can't stay between the pad and the rotor, it forms a thin layer between the two whilst trying to escape. The pads lose contact with the rotor, reducing the amount of friction, and the result is brake fade.

The typical remedy for this would be to stop the vehicle and wait for a few minutes. As the brake components cool down, their ability to absorb heat returns and the next time you use the brakes, they work just fine. This type of brake fade was more common in older vehicles. Newer vehicles tend to have less out-gassing from the brake pad compounds but they still suffer brake fade.

Why? It's still to do with the pads getting too hot. With newer brake pad compounds, the pads transfer heat into the calipers once the rotors are too hot, and the starts to boil, forming bubbles in it. Because air is compressible (brake fluid isn't) when you step on the brakes, the air bubbles compress instead of the fluid transferring the motion to the brake calipers. Once again, the result is brake fade.

So how do the engineers design brakes to reduce or eliminate brake fade? In older vehicles, you give the vaporised gas somewhere to go. For newer vehicles, you find some way to cool the rotors off more effectively. Either way, you end up with cross-drilled or grooved brake

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 91 rotors. While grooving the surface may reduce the specific heat capacity of the rotor, its effect is negligible in the grand scheme of things. However, under heavy braking once everything is hot and the resin is vapourising, the grooves give the gas somewhere to go, so the pad can continue to contact the rotor, allowing you to stop.

The whole understanding of the conversion of energy is critical in understanding how and why brakes do what they do, and why they are designed the way they are. If you've ever watched Formula 1 racing, you'll see the front wheels have huge scoops inside the wheel pointing to the front (see the picture above).

This is to duct air to the brake components to help them cool off because in F1 racing, the brakes are used viciously every few seconds and spend a lot of their time trying to stay hot. Without some form of cooling assistance, the brakes would be fine for the first few corners but then would fade and become practically useless by half way around the track.

Rotor technology. If a brake rotor was a single cast chunk of steel, it would have terrible heat dissipation properties and leave nowhere for the vapourised gas to go. Because of this, brake rotors are typically modified with all manner of extra design features to help them cool down as quickly as possible as well as dispel any gas from between the pads and rotors.

The diagram shows some examples of rotor types with the various modification that can be done to them to help them create more friction, disperse more heat more quickly, and ventilate gas.

From left to right: 1: Basic brake rotor. 2: Grooved rotor - the grooves give more bite and thus more friction as they pass between the brake pads. They also allow gas to vent from between the pads and the rotor. 3: Grooved, drilled rotor - the drilled holes again give more bite, but also allow air currents (eddies) to blow through the brake disc to assist cooling and ventilating gas.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 92 4: Dual ventilated rotors - same as before but now with two rotors instead of one, and with vanes in between them to generate a vortex which will cool the rotors even further whilst trying to 'suck' any gas away from the pads.

An important note about drilled rotors: Drilled rotors are typically only found (and to be used on) race cars. The drilling weakens the rotors and typically results in microfractures to the rotor. On race cars this isn't a problem - the brakes are changed after each race or weekend. But on a road car, this can eventually lead to brake rotor failure. Big rotors. How does all this apply to bigger brake rotors - a common sports car upgrade? Sports cars and race bikes typically have much bigger discs or rotors than your average family car. A bigger rotor has more material in it so it can absorb more heat. More material also means a larger surface area for the pads to generate friction with, and better heat dissipation. Larger rotors also put the point of contact with the pads further away from the axle of rotation. This provides a larger mechanical advantage to resist the turning of the rotor itself.

To best illustrate how this works, imagine a spinning steel disc on an axle in front of you. If you clamped your thumbs either side of the disc close to the middle, your thumbs would heat up very quickly and you'd need to push pretty hard to generate the friction required to slow the disc down. Now imagine doing the same thing but clamping your thumbs together close to the outer rim of the disc. The disc will stop spinning much faster and your thumbs won't get as hot. That explains the whole principle behind why bigger rotors = better stopping power. The different types of brakes All brakes work by friction. Friction causes heat which is part of the kinetic energy conversion process. How they create friction is down to the various designs.

Bicycle wheel brakes Bicycle wheel brakes are the most basic type of functioning brake that you can see, watch working, and understand. The construction is very simple and out-in- the-open. A pair of rubber blocks are attached to a pair of calipers which are pivoted on the frame.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 93

When you pull the brake cable, the pads are pressed against the side or inner edge of the bicycle wheel rim. The rubber creates friction, which creates heat, which is the transfer of kinetic energy that slows you down. There are only really two types of bicycle brake - those on which each brake shoe shares the same pivot point, and those with two pivot points.

Once you understand how brakes work on a bicycle, you’ll find it easier to understand how brakes work on a car.

Drum brakes - single leading edge The next, more complicated type of brake is a . The concept here is simple. Two semicircular brake shoes sit inside a spinning drum which is attached to the wheel. When you apply the brakes, the shoes are expanded outwards to press against the inside of the drum. This creates friction, which creates heat, which transfers kinetic energy, which slows you down. The example below shows a simple model. The actuator in this case is the blue elliptical object. As the actuator is twisted, it forces against the brake shoes and in turn forces them to expand outwards. The return spring is what pulls the shoes back away from the surface of the brake drum when the brakes are released. See the later section for more information on actuator types.

The "single leading edge" refers to the number of parts of the brake shoe which actually contact the spinning drum. Because the brake shoe pivots at one end, simple geometry means that the entire brake pad cannot contact the brake drum.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 94

The leading edge is the term given to the part of the brake pad which does contact the drum, and in the case of a single leading edge system, it's the part of the pad closest to the actuator.

This diagram (right) shows what happens as the brakes are applied. The shoes are pressed outwards and the part of the brake pad which first contacts the drum is the leading edge. The action of the drum spinning actually helps to draw the brake pad outwards because of friction, which causes the brakes to "bite". The trailing edge of the brake shoe makes virtually no contact with the drum at all.

This simple geometry explains why it's really difficult to stop a vehicle rolling backwards if it's equipped only with single leading edge drum brakes. As the drum spins backwards, the leading edge of the shoe becomes the trailing edge and thus doesn't bite.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 95 Drum brakes - double leading edge The drawbacks of the single leading edge style of drum brake can be eliminated by adding a second return spring and turning the pivot point into a second actuator. Now when the brakes are applied, the shoes are pressed outwards at two points, so each brake pad now has one leading and one trailing edge. Because there are two brake shoes, there are two brake pads, which means there are two leading edges. Hence the name double leading edge.

Disc brakes Disc brakes are very much better at stopping vehicles than drum brakes, which is why you'll find disc brakes on the front of almost every car and motorbike built today. Sportier vehicles with higher speeds need better brakes to slow them down, so you'll probably see disc brakes on the rear of those too.

Disc brakes are again a two-part system. Instead of the drum, you have a disc or rotor, and instead of the brake shoes, you now have brake caliper assemblies. The caliper assemblies contain one or more hydraulic pistons which push against the back of the brake pads, clamping them together around the spinning rotor.

The harder they clamp together, the more friction is generated, which means more heat, which means more kinetic energy transfer, which slows you down. The explanation is always the same!

Standard disc brakes have one or two cylinders in them - also know as one or two-pot calipers. Where more force is required, three or more cylinders can be used. Sports bikes have 4- or 6-pot calipers arranged in pairs. The disadvantage of disc brakes is that they are extremely intolerant of faulty workmanship or bad machining. If you have a regular car disc rotor which is off by so much as 0.07mm (3/1000 inch)

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 96 you’ll have huge problems when you step on the brakes. That ever-so- slight warp or misalignment is going to spin through the clamped calipers at enormous speed and the resulting vibration will make you wonder if you're driving down stairs. To combat this problem, which is particularly critical on motorbikes, floating rotors were invented.

Brake pad compounds Most pads used to use asbestos but this has been discontinued because of the dangers of the material. Today, many combinations of materials are used.

The pads themselves are made up of a friction material bonded to the backing plate. The brake caliper piston pushes against the backing plate and the friction material is pushed against the brake rotor. The material combinations typically fall into the following broad categories:

Organic These pads are well-suited for street driving because they wear well, are easy on the ears, don't chew up the rotors and don't spew dust everywhere. They're favoured for your average family saloon because they work well when they're cold. The drawback is that they don't work so well when they get hot.

Semi-metallic / sintered This is a good compromise between street and track. These seem to be the pad of choice for sportier vehicles such as the Subaru Impreza WRX. They don't work as well as organic pads when they are cold, so the driver needs to be a bit careful of the first couple of stops. Conversely, they do work well when hot. Occasionally the weak link in semi-metallic pads is the bonding material that holds the friction pad to the backing plate.

Metallic These pads are typically reserved for racing or the extremely rich. They squeal and dust badly, are hard on rotors and don't work well when cold.

Ceramic Ceramic pads still have metal fibres (about 15% vs. about 40% for semi-metallic) but they are copper instead of steel and therefore cause less wear and transfer heat better. They don't fade as easily

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 97 as other pads, cool faster, last longer, and are effectively silent, as the sound they generate is outside the human range of hearing. The dust created by ceramic pads is also very light in colour so your wheels look cleaner.

Brake squeal Squealing brakes are a sign of one of two things: the friction material is worn out and you're jamming the backing plate against the brake rotor, or the fit of the brake pad against the caliper piston isn't as snug as it could be. Either way, the squealing is the result of an extremely high- frequency vibration between the pad, the caliper piston and the brake rotor.

Solving brake squeal A good way to solve brake squeal is to put some copper-based grease on the back of your brake pads.

That's very important: THE BACK of your brake pads.

Copper grease is extremely resistant to pressure and heat and if you get any on the front of your pads, you'll need new pads and rotors or discs. The idea is that it creates a small pocket of sticky lubrication between the front side of the brake pistons and the back side of the brake pads. This is usually enough to prevent the high-frequency squeal.

Copper grease and rubber Whilst copper grease works well in the short term to solve brake squeal, long-term, it has an adverse affect on the rubber dust seals of the calliper pistons. This can lead to the seal deteriorating or failing completely. If that happens, it leaves the piston and its surface exposed to the very elements from which it should be protected.

The other solution to brake squeal Whilst the ultra high frequency vibration is one cause of brake squeal, the other major cause is related to suspension alignment. Driving on badly-maintained roads, or through pot-holes, all make the suspension

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 98 move around in ways it was never really designed to cope with, and this in turn leads to the suspension bushes becoming stressed.

Normally, re-aligning the wheels on a vehicle is corrected by mechanical adjustment only. If the mounting rubbers are not de- stressed first, then it leads to the transfer of the sound generated during braking into the chassis and body which then amplifies it to a level at which we can hear it. It is like a giant record player with the suspension as the pickup needle and the entire car as the speaker. If you have squealing brakes that copper grease doesn't solve, look into a proper suspension realignment and possibly new suspension bushes.

Brake actuators Brakes are all well and good, but you need some method of applying them in order for them to work. The method by which the force from your hand or foot reaches the brake itself is all to do with the brake actuator system.

Cable-operated This is about as basic as you get. A cable is connected to a lever at each end. You press on one lever with your foot or squeeze it with your hand, and it pulls the lever at the other end. On the back of the brake-end lever there's an elliptical cam which rotates inside a circular cup in the brake shoe. As the long axis of the ellipse rotates, it forces the brake shoes to move apart.

Solid bar connection

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 99 One step up, and found on the rear brake of older motorbikes, is the solid bar connection. This allows the use of mechanical advantage to amplify your force on the pedal or lever before it gets to the brakes themselves. Typically these systems are used on drum brakes with the elliptical actuator described above. The disadvantage of this system is that it needs hinge and pivot points that match the position of the suspension components, or, going over a bump could put the brakes on as the suspension moves relative to the lever.

Single-circuit hydraulic

Another step up and we get to the type of brake system used on most cars and motorbikes today. Gone are the cables and bars, replaced instead by a system of plungers, reservoirs and hydraulic fluid. Single- circuit hydraulic systems have three basic components - the master cylinder, the slave cylinder and the reservoir. They're joined together with hydraulic hose and filled with a non-compressible hydraulic fluid (see brake fluid below).

When you press your foot on the brake, or squeeze the brake lever, you compress a small piston assembly in the master cylinder. Because the brake fluid does not compress, that pressure is instantaneously transferred through the hydraulic brake line to the slave cylinder where it acts on another piston assembly, pushing it out. That slave assembly is either connected to a lever to activate the brakes, or more commonly, is the brake caliper itself, with the slave cylinder being the piston that acts directly on the brake pads. Because of the arrangement of the slave cylinder, heat from the brakes can be transferred back into the brake fluid.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 100 Dual-circuit hydraulic

Dual-circuit hydraulic systems are available on high-end luxury vehicles and newer motorbikes. These have two separate circuits. One is the command circuit - that's the one you act on with your hand or foot.

The second is a separate circuit controlled by an onboard computer, and that's the one which is actually connected to the brakes. As you apply the brakes, you're sending a pressure signal via the command circuit to the brake computer.

It measures the amount of force you're applying, and using a servo / pump system, applies the same force to the secondary circuit to activate the brakes. If you do something stupid like trying to slam on the brakes at 100kph, the computer will realise that this would result in a skid or spin, and will not send the full pressure down the secondary circuit, instead deciding to use its speed and ABS sensors to determine the optimal brake pressure to maintain control of the vehicle. The advantage of a dual-circuit system is that the command circuit never gets heat transferred into it because it is totally separated from the brakes themselves. The disadvantage of course is that there are now two hydraulic circuits to maintain.

Brake-by-wire The most advanced system of brakes to date is brake-by-wire. These are a direct copy of some styles of racing brakes and are very similar to the dual-circuit hydraulic system described above, but instead of the command circuit being hydraulic,

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 101 it's replaced by electronics. The brake pedal or lever is connected to a hypersensitive rheostat (measures electrical resistance).

The more you push it, the greater the electrical signal sent to the brake computer. After that, it performs just like the secondary circuit described above. The advantage to this system is that the brake pedal or lever can be placed just about anywhere you like as it no longer is encumbered by the plumbing that goes with a hydraulic circuit. To combat driver complaints of "lack of feel" in the brakes, most brake-by- wire systems have a reverse feedback loop built in. This measures the pressure being applied to the brakes on the secondary circuit, and actuates an electrical resistor in the pedal or lever assembly to provide resistance. This is needed because there is no physical connection to any part of the brake system at all.

Mechanical advantage If you did any sort of physics classes when you were at school, you might remember something called mechanical advantage. In its most basic form, mechanical advantage is the ratio of force-in to force-out in a mechanical system. Mechanical Advantage = Effort Torque/Load Torque.

For example a 20kg weight 1 metre from a pivot can lift a 40kg weight 0.5m from the pivot on the other side. The effort torque and load torque calculations are to do with force in Newtons and distance from pivot point. Hence torque is measured in Newton-metres, or Nm.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 102

A Newton is the amount of force required to accelerate a mass of one kilogram by one metre per second². On Earth, where acceleration due to gravity is 9.8m/s², the force exerted upon a mass of 1kg is 9.8N (usually rounded up to 10N). Another popular notation is lbf.ft - pound- force-feet, commonly referred to as foot-pounds. 1 Newton-metre is equivalent to 0.737 foot-pounds.

The diagram above shows a simple lever system on a pivot. The load torque is 200Nm, and the effort torque is also 200Nm. Mechanical advantage = effort / load, which in this case is 200 / 200, which is 1. ie. the system is balanced.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 103 Now imagine increasing the weight on the effort side to 30kg instead of 20kg, but leaving everything else the same. The load torque is still 200Nm, but the effort torque is now 300Nm. Mechanical advantage = effort / load, which is 300 / 200, which is 1.5. Any mechanical advantage value larger than 1.0 means that the effort has the advantage. In this case, a 30kg weight which is lighter than the 40kg load, is able to lift it off the ground.

If you now take your knowledge about physics and look at the simple lever brake system, you'll realise how it's possible to generate enough force using your foot to stop a car or motorbike. Look at this diagram of the lever-operated cam brake.

This system has 4 levers in it. The middle two have no mechanical advantage as the levers are connected the same distance from the

pivot in each case. However, look at the pedal. The values are arbitrary but they serve the purpose. On the pedal we have some amount of force 20cm from the pivot, but the other end of the lever is only 5cm from the pivot. This gives us a mechanical advantage of 4 on the brake lever (20cm / 5cm).

At the other end, the lever attached to the cam is still a lever system - it's just bent. The input lever is 10cm long but the cam is only 4cm across - or 2cm to the tip from the pivot. So at the brake cam we have a mechanical advantage of 5. (10cm / 2cm). So across this entire system, we have a total mechanical advantage of 20 - 4 from the brake pedal and 5 from the lever and cam. Apply force to this little system and be amazed.

The units of force used are irrelevant - they're multiplied just the same. To use easier-to-comprehend values, let's imagine that when you're braking, your foot is pushing on the brake pedal with about 60pounds of

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 104 force - 27Kg. Through the brake pedal, that is amplified 4 times to 240pounds, and through the lever and cam it is amplified a further 5 times from 240pounds to 1200pounds. You pushed the pedal with 60pounds of force, but the cam inside the drum brake is being forced out against the brake drum with 1200pounds of force - about 544Kg!

Mechanical advantage as applied to hydraulics Most braking systems now use hydraulics. This is a slight change in the equation but the concept of mechanical advantage still exists, this time by the use of pressure equations. Pressure = force / area. If you apply 20 Newtons of pressure to 1m², it's the same as applying 200 Newtons to 10m². Why? Because 20 Newtons of force divided by 1m² of area generates 20 Pascals of pressure. Similarly, 200N / 10m² is also 20Pa.

If you now think of that in terms of a hydraulic braking system, it becomes clear how mechanical advantage works for you. Brake fluid is incompressible - it has to be. This is good because it makes calculation for hydraulic brake systems quite easy - you can eliminate the internal pressure from the equation.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 105 Split the system into two parts - input and output - the brake pedal and the brake caliper piston. For each part, Pressure = Force / Area.

The pressure is the same at all points in the system, so some basic algebra gives a simple formula.

Using our previous example, we apply 60pounds (27Kg) of input force to the brake pedal. This is attached to a master piston which (for example) is 1.25cm across - i.e. it has a surface area of 0.000491m² (remember your maths? Area = PI x r²).

At the other end of the system is the caliper piston, which for example is 2cm across - i.e. it has a surface area of 0.001257m².

Using our formula, the output force from the caliper piston is 60 x (0.001257m² / 0.000491m²) Get your calculator out and that comes out to 154pounds (69.8Kg) - more than double the force at the brake pedal. The ratio of output area to input area is sometimes referred to as the area differential.

Power brakes and master cylinders Power brakes (also known as power assisted brakes) are designed to use the power of the engine and/or battery to enhance your braking power. Whilst you can generate a fair amount of force using your foot, using systems from elsewhere in the car to help you apply even more force means that you get more powerful brakes as a result.

The four most common types of power brakes are: vacuum suspended; air suspended; hydraulic booster, and electrohydraulic booster. Most cars use vacuum suspended units (vacuum boosters). In this type of system, when you press the brake pedal, the push rod to the master cylinder opens a vacuum control valve. This allows vacuum pressure (normally from the intake manifold) to "suck" on a diaphragm inside the vacuum assist unit. This extra vacuum suction helps you to produce more force at the pedal end of the brake system.

Hydraulic booster systems usually utilise pressure from the system to augment pressure on the master brake cylinder.

Electrohydraulic booster systems use an electric motor to pressurize

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 106 the hydraulic system downwind of the brake pedal which has the effect of amplifying the internal pressure in the whole system.

The advantage of this system is that as long as you have battery power, you have power brakes even if the engine fails. With vacuum- assist brakes, no engine means no assistance.

If you're curious about how power brakes work, go out to your car and with the engine off, step on the brakes. They'll have a slightly solid, almost wooden feel to them. Turn the engine on and do it again and you'll notice a lot less back-pressure on the pedal. This is the power assist which is making it easier for you to depress the pedal.

The components of a master cylinder Brake master cylinders are complicated affairs involving finely

manufactured parts, minute tolerances, springs, o-rings and rubber seals. The diagram here is a simplified representation of a dual-circuit master brake cylinder. When you step on the brake, it’s connected to the main plunger (on the right side of this image). As this is pushed into the master cylinder, it acts on the components inside.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 107 The rear plunger (in blue) is the first one to move forward, brake fluid from the reservoir is sucked in through the fluid intake and return port. At the same time, fluid is sucked in through the equalisation port. As the second circuit rear seal passes the intake and return port (about 1.5mm after the plunger starts moving), it creates a fixed volume of fluid between the rear and front plungers. The more you step on the brake pedal, the more this fluid is forced out into the second brake circuit to apply the brakes.

At the same time, the pressure building up in this area overcomes the strength of the first circuit return spring and the front plunger (red) begins to move too. As with the rear plunger, it too sucks fluid from the reservoir until the first circuit rear seal passes the fluid intake and return port (again about 1.5mm), trapping fluid between it and the front of the master cylinder. This fluid is then forced out into the first brake circuit, applying those brakes.

When you take your foot off the brakes, the return springs push the plungers back into their neutral position. Fluid returns to the brake fluid reservoir and the system goes back to an unpressurised state.

Cross-linked brakes - why there are two brake circuits

In this rendering of the master brake cylinder, you'll see there are two plungers and two brake circuits. This is the most common design for cars today. It's a form of redundancy in the brake system. The idea is that only two brakes, one front and one rear, are on either of the brake circuits.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 108 For four brakes, you therefore need two circuits. But why? Imagine one of your brake lines springs a leak - for the sake of argument, the front-left brake. If all four brakes were on a single circuit, when the master cylinder began to pressurise the brake system, fluid would spurt out of the broken line and pressure would never build up. In turn, that means none of the brakes would ever come on and you'll drive into the back of the vehicle in front of you.

Imagine the same scenario with two circuits. As the first circuit pressurises the front-left and rear-right brakes, fluid spurts out of the broken line and those brakes are never applied. However because the master cylinder is also pressurising a separate second circuit connected to the front-right and rear-left wheels, those brakes do apply and you've still got braking force. It's reduced, but it's a lot better than no brakes at all. Because of the front-left to rear-right and front-right to rear-left linking of the brake circuits, this type of system is known as cross-linked brakes. The rendering here shows an example arrangement of cross-linked brakes.

A word about handbrakes It's worth spending a moment here to talk about handbrakes. Whilst they're good for doing handbrake turns, they're not especially effective at actually slowing you down. Handbrakes are cable-actuated so the amount of power they have is wholly dependent on the amount of tug you have in your arm. There's no hydraulic system to help you out. Apart from that, they only work on the rear wheels, so you're not getting four-wheel braking. On drum-brakes, the handbrake is connected to a small lever that pivots against the end of one of the brake actuating pistons. When you pull the handbrake, the lever gets pulled and the brake shoes are pressed out against the inside of the drum.

On disc brakes, the handbrake normally works a second set of brake pads in the rear caliper. They're little spots, about the size of a grown man's thumbprint and they're clamped mechanically against the brake rotor. These pads never need changing because they're normally only used at standstill so generally don't wear

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 109 much. Their small size is the other reason you shouldn't expect excellent stopping performance if you yank on the handbrake.

Anti lock Braking Systems - ABS Stop without skidding, and maintain control of the vehicle. That's the premise of ABS. It was first introduced in the 1980's and has been undergoing constant refinement ever since. The system is typically comprised of 4 ABS rings, 4 sensors, an ABS computer and a number of pressure-management circuits in the brake lines. The ABS rings are attached either to the wheels, or more often, to the brake discs. They look like a notched ring - see the image to the right.

The sensors are magnetic field sensors which are held very close to the ABS rings and can detect the slight change in magnetic field as the teeth on the ring pass them. The pulsing field tells the ABS computer that the wheels are spinning, and how fast they're spinning.

When you brake, the wheel rotation starts to slow down. The ABS computer "listens" to the input from the sensors and can detect if one wheel is slowing down much quicker than the others - the precursor to the wheel locking up - this all happens in milliseconds. When the computer detects this condition, a pressure regulator in the brake circuit interrupts the pressure in the brake lines by momentarily reducing it so that the brakes release just enough to give the wheels a chance to keep spinning rather than locking up.

The computer then instructs the regulator to re-apply full pressure and again measures the wheel rotation. This on/off/measure cycle happens around 15 to 30 times a second. If the ABS kicks in, you'll feel it through the brake pedal as a vibration because the pulsing in the brake circuit affects all the components.

Newer generation ABS systems As technology marches on, so does the control / feedback system used in ABS. It used to be the case that any single wheel approaching lockup would cause the ABS system to pulse the brake pressure for all the wheels. On modern vehicles, the ABS computer is connected to 4 pressure regulators instead of just one.

This means it can selectively apply pulsed braking only to the wheel(s) that need it. So if three of the tyres are gripping well, but the front-left is beginning to skid, the ABS can unlock the front-left brake and pulse it to

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 110 try to regain grip. It's called three- or four-circuit ABS. When hooked up to the traction control system, this type of multi-circuit ABS can also be used to influence the overall traction of a car in extreme manoeuvres, such as helping to prevent rollover and inside-wheel-lifting.

ABS and skid control The biggest misconception about ABS is that it will make you come to a stop more quickly. This is a sensitive topic. In one camp you have drivers who can't tolerate the idea of a computer breaking the physical connection between the driver’s foot and the brake system.

In the other camp you have people who believe that ABS will help you stop faster, and in certain conditions, this is true. On a wet or greasy road surface where the traction is severely reduced, an ABS system can pulse the brakes and prevent lockup much better than a human can.

But why? The whole point of brakes is to slow you down. To do that they rely on friction in two places - between the brake pads and the rotors, and between the tyres and road surface. If one of those factors is taken out of the equation, the brakes become useless. The most typical situation is that a driver will panic-react to something and step on the brakes with as much power as he can muster. The brake system amplifies this power, grabs hold of the brake rotors and the wheels stop turning almost instantly.

This causes the tyres to skid across the road surface, and as they do so, they become subject to dynamic attrition. In other words, if a tyre is

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 111 rotating and gripping the road, the "stick" factor is much higher than if the wheel is locked and skating across the same surface. So that's what ABS does - in an emergency, it ensures that the wheels don't lock up but instead keep spinning so that the tyres maintain grip with the road. (That's where ABS gets its name - Anti-Lock Brakes.) This is where the real benefit of ABS comes into play. If you're going to attempt to avoid an accident, the best thing to do is to try to steer around it.

If your tyres are skidding on the road surface, you can point your wheels wherever you want because your actual direction will have nothing to do with the wheels and everything to do with the direction in which you were travelling, combined with the camber of the road.

Once the tyres lose grip, the vehicle is completely out of control. With ABS, if the wheels keep turning and the tyres keep gripping, then when you grab the steering and yank it to one side, the car will still turn and you might be able to avoid the accident. So that's the true essence of ABS - to maintain control over the direction of the car.

Brake-assist and collision warning systems By 2006, brake-assist and accident warning systems were starting to find their way into consumer cars.

Volvo's collision warning system (CWS), for example, constantly monitors your speed and uses a radar with a 15° forward field of view to determine the distance to any object in front of you. If the distance begins to shrink but you don't slow down, the system sounds a buzzer and flashes a bright red light in a heads-up display to alert you.

The brake pads are automatically placed against the discs and when the driver finally does use the brakes, the system monitors the pedal pressure. If the pressure is determined to be too light, the braking power is amplified by the system.

Brake-assist and auto-brakes go one step further. In some high end vehicle now (top end BMWs and Mercedes' for example), the collision- detection system is linked into the brakes like it is with the Volvo system, but it's also been given the flexibility to do all the braking for you.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 112 Adaptive cruise control, for example, will control the throttle just like a normal cruise control system, but will also apply the brakes if it determines that you're getting too close to the vehicle in front. Full auto- brakes will actually stop the car for you if you fail to respond. All these systems work in essentially the same way - they monitor the brake use and distance to the vehicle in front. If the computer thinks you're not braking hard enough, it will assist you.

Other brake technologies There are other brake technologies that are becoming available in vehicles now, and a lot of them are gathered together in the 2006 / 2007 BMW models. Three of the more notable features are:

 Brake Drying. The X3 has rain-sensing windscreen wipers. When they sense rain, they also send information to the onboard computer. In turn, it goes into a cycle of occasionally bringing the pads into light contact with the brake rotors. This generates enough friction to eliminate any film of water that might be on the surface of the rotors, but not enough that it slows the car down or is even detectable by the driver.

 Brake Stand-by. This is a pre-emptive system that attempts to detect when sharp braking is about to happen. Potentiometers attached to the accelerator can detect when the driver takes their foot off it very quickly. That would normally be followed by the brake being applied very quickly. When the onboard computer senses this condition, it moves the brake pads right up to the rotors using the same mechanism that the brake drying system uses. Ultimately, if the driver does jump on the brakes, they're ready to work the millisecond the driver's foot touches the pedal. It may not sound much but that tiny difference in distance moved, translates into a saving in time between putting your foot on the brake and the car actually slowing down. That in turn translates into forward distance - or less of it.

 Brake Fade Compensation. Brake fade was described earlier. If the brake rotor temperature begins to rise, this system increases the hydraulic pressure used to press the pads against the rotors without requiring any more pressure on the brake pedal.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 113 These three brake technologies don't actually attempt to compensate for any wrongdoing on the driver's behalf. They simply prepare the car for when the driver chooses to use the brakes.

Brake hoses - not just rubber Obviously with all the pressure in your brake system, the last thing you need is for the brake lines themselves to deform and flex. If they do, you lose brake pressure, and thus lose braking. Steel brake lines are no problem, but for the flexible areas of the brake lines, you need hoses. Brake hoses come in two basic flavours.

Rubber hoses The humble rubber hose on your brake lines is not so humble. The hose itself is actually made of three parts. The inner liner is a corrosion and brake-fluid resistant compound designed (normally PTFE / Teflon® based) purely to keep the brake fluid in. Around the outside of that, there's a steel webbed mesh. This is what gives the brake hose its strength and stops it from bulging and deforming. And around the outside of that there's a slightly thicker rubber coating, which is there to weatherproof the steel mesh. The three layers together give strength, flexibility and durability.

Steel-braided hoses Steel-braided hoses are a slightly different design. They only really have two components - the inner hose which carries the brake fluid and is lined with a PTFE compound, and the outer steel braid which contains and flexing or bulging. Steel-braided lines resist bulging a lot better than rubber hoses. One downside is that the steel braiding itself is totally merciless and if it finds something to rub against in the vehicle, it will rub right through it, even if it's an alloy.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 114 For that reason, a lot of braided brake hose manufacturers put a third layer - a thin transparent rubber sheath around the outside simply to keep everything in check and prevent scuffing and rubbing.

Brake fluids Brake fluid does not compress. It's a good job too - if you put your foot on the brake pedal and it went all the way to the floor, you'd be worried. But that's exactly what can happen if you disregard the "health" of your brake fluid.

Brake fluid is hygroscopic - that means it attracts and soaks up water. This is why it comes in sealed containers when you buy it. The problem is that if it does start to take on water, bad things can happen.

Your typical DOT 4 brake fluid (see later for DOT ratings) boils at about 446°F (230°C). Water boils at 212°F (100°C). Imagine your brakes are getting hot because of a long downhill stretch. Whilst the brake fluid is quite OK, the temperature of the brake components might get up over the boiling point of water. If that happens, the water boils out of the brake fluid and forms steam - a compressible gas. Next time you put your foot on the brake, rather than braking, all the pressure in the brake system is taken up with compressing the steam. Your brakes go out, and you don't stop.

Getting a little more complex, the boiling point of a liquid goes up with its pressure. So when you step on the brake, the boiling point of the brake fluid might actually go up to 500°F (260°C) and the boiling point of the water content might raise up to 250°F (121°C).

Now the boiling point is higher than the temperature of the brake fluid. At least it is until you take your foot off the brake again. Now the pressure in the system returns to normal, the boiling points revert to normal and instantly the water boils off into steam again. The symptoms are slightly different now. Under this scenario, the brakes

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 115 work the first one or two times, but on the third or fourth press, they stop working because the temperature and pressures have conspired to boil the water.

The worst possible scenario is brake-fade (see right at the top) combined with air in the system. This means that you have no brakes at all.

D.O.T. ratings All brake fluids are DOT rated. Your owner’s handbook for your car or motorbike probably tells you to use DOT3 or DOT4 from a sealed container. The DOT ratings are a set of minimum standards the fluid must adhere to in order to get the rating, and thus work in your braking system. The following table shows the various properties of DOT ratings. Remember that the values here are the minimum values. Most manufacturers make sure their product far exceeds minimum ratings.

Boiling DOT DOT DOT 5 (silicone- DOT 5.1 (non-silicone Point 3 4 based) based) Dry 205°C 230°C 260°C 260°C Wet 140°C 155°C 185°C 185°C converted to °Celsius by editor

The "dry" and "wet" boiling points in the table above are for brake fluid which is fresh from the bottle (dry) and which has a 10% water content (wet). A DOT study in 2000 discovered that on average, the brake fluid in a vehicle absorbs about 2% water every 12 months.

The two types of brake fluids shown in the table are DOT3/DOT4/DOT5.1 which are glycol (Polyalkylene Glycol Ether) based, and DOT5 which is silicone based. DOT3 and DOT4 fluids are interchangeable* - the only real difference is their boiling point.

DOT3/4/5.1 and DOT5 fluids cannot be mixed or interchanged under any circumstances. They do not mix at all and the silicon based fluids can destroy the seals in brake systems which rely on the moisturiser additives that are present in DOT3/4/5.1 fluids.

Other things you ought to know about silicone based fluids:

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 116 - they are resistant to absorbing water, which is why their wet boiling points are so high. The problem is that any water content eventually pools in the low spots of the brake system and causes rust. - they don't strip paint. - they are not compatible with most ABS system because they doesn't lubricate the ABS pump like a glycol based fluid. - putting this fluid in systems which have had DOT3/4 fluid in will cause the seals in the caliper and master cylinders to malfunction - which means they need replacing, which is expensive.

Brake warning lights Most cars nowadays have a brake warning light on the dashboard. Its purpose is to alert you that something is wrong in the braking system somewhere. If it comes on, check your owner's manual to find out its meaning. Unlike the single-purpose ABS warning light, the brake warning light doesn't have a standard meaning; it could be used for multiple purposes.

For example, the same light may be used to show that the hand brake is on. If that's the case and you're driving, you ought to have noticed the smell of burning brake dust. The light can also indicate that the fluid in the master cylinder is low. Each manufacturer has a different use and standard for this light.

If you've got an ABS-equipped car, you also have a second light - the ABS light. If it comes on, get it seen to as soon as possible. It means the ABS computer has diagnosed that something is amiss in the system. It could be something as simple as dirt in one of the sensors, or something as costly as an entire ABS unit replacement.

Either way, if that light is on, then you have a major problem. It's important to note that this light normally comes on when you start the car and then switches off a few seconds later. If it stays on, blinks, throbs, flashes or in any other way draws your attention to itself, take note.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 117

LED replacement bulbs You might have seen automotive shops stocking LED replacement bulbs for cars and motorbikes. The most basic replacements look like those on the right - a cluster of 19 or 24 LEDS (light emitting diodes) in a housing with a regular push-fit or bayonet plug on the back. The idea is that if you want brighter lights, you can replace your tail or turn lights with these LED replacements. But take care - a lot of vehicles (cars and motorbikes) have onboard diagnostics which include a light check. Some of these use resistance to figure out if a bulb has blown.

LED clusters have a radically different resistance to a filament bulb and it’s possible that when you replace your bulbs with LED versions, your car will continuously tell you that one or more bulbs is burned out. Getting one step more severe, if you use LED turn bulbs, your indicators could flash quicker or slower than you're used to (indicator circuits use the natural resistance of the bulbs in conjunction with the relay to dictate the flash speed).

SUSPENSION SECTION back to ToC What does it do? Apart from your car's tyres and seats, the suspension is the prime mechanism that separates you from the road. It also prevents your car from shaking itself to pieces.

In its most basic form, suspension consists of two basic components:

Springs These come in three types. They are coil springs, torsion bars and leaf springs. Coil springs are what most people are familiar with, and are actually coiled torsion bars. Leaf springs are what you would find on most American cars up to about 1985 and almost all heavy duty vehicles. They look like layers of metal connected to the axle. The layers are called leaves, hence leaf-spring.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 118 The torsion bar on its own is a strange little contraption which gives coiled-spring-like performance based on the twisting properties of a steel bar. It's used in the suspension of VW Beetles and the rear suspension of Peugeot 205s amongst other cars.

Instead of having a coiled spring, the axle is attached to one end of a steel shaft. The other end is slotted into a tube and held there by splines. As the suspension moves, it twists the shaft along its length, which in turn resist. Now image that same shaft instead of being straight, being coiled up. As you press on the top of the coil, you're actually inducing a twisting in the shaft, all the way down the coil. I know it's hard to visualise, but believe me, that's what is happening. There's a whole section further down the page specifically on torsion bars and progressive springs.

Shock absorbers These dampen the vertical motion induced by driving your car along a rough surface and so should technically be referred to by their 'proper' name - dampers. If your car only had springs, it would boat and wallow along the road until you got physically sick and had to get out. It would be a travelling death-trap. Or at least it would be a travelling death-trap until the incessant vibration caused it to fall apart. Shock absorbers (dampers) perform two functions. As mentioned above, they absorb any larger-than-average bumps in the road so that the upward velocity of the wheel over the bump isn't transmitted to the car chassis. But secondly, they keep the suspension at as full a travel as possible for the given road conditions - they keep your wheels planted on the road.

Technically they are velocity-sensitive hydraulic damping devices - in other words, the faster they move, the more resistance there is to that movement. They work in conjunction with the springs. The spring allows movement of the wheel to allow the energy in the road shock to be transformed into kinetic energy of the , whereupon it is dissipated by the damper.

The damper does this by forcing gas or oil through a constriction valve (a small hole). Adjustable shock absorbers allow you to change the size of this constriction, and thus control the rate of damping. The smaller the constriction, the stiffer the suspension.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 119 Suspension types There are a large number of different types of suspension available for both front and rear axles. The main groupings are dependent and types but this naming convention really only applies to traditional or analogue suspension systems. Even independent systems are typically joined across the car by an anti-roll bar and so are not truly independent.

From about 2006 onwards, the concept of fully independent suspension systems started to appear on cars where the anti-roll bar was replaced by sophisticated computer software connected to some form of electronically-controlled suspension.

Front suspension - dependent systems This system gets its name because the front wheel's suspension systems are physically linked. For everyday use, they are of very little value.

The most common type of dependent system is basically a solid bar under the front of the car, kept in place by leaf springs and shock absorbers. It's still common to find these on trucks, but not on cars. They haven't been used on mainstream cars for years for three main reasons:

 Shimmy - because the wheels are physically linked, the beam can be set into oscillation if one wheel hits a bump and the other doesn't. It sets up a gyroscopic torque about the steering axis which starts to turn the axle left-to-right. Because of the axle's inertia, this in turn feeds back to amplify the original motion.  Unsprung weight - solid front axles weigh a lot and either need sturdy, heavy leaf springs or heavy suspension linkages to keep their wheels on the road.  Alignment - simply put, you can't adjust the alignment of wheels on a rigid axis. From the factory, they're perfectly set, but if the beam gets even slightly distorted, you can't adjust the wheels to compensate.

However, this is probably the best suspension system for off-road use. Front suspension - independent systems So-named because the front wheel's suspension systems are independent of each other (except where joined by an anti-roll bar)

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 120 These came into existence around 1930 and have been in use in one form or another pretty much ever since then.

MacPherson strut or McPherson strut This is currently the most widely used front suspension system in cars of European origin. It is simplicity itself. The system basically comprises a strut-type spring and combo, which pivots on a on the single, lower arm.

At the top end there is a needle roller bearing on some more sophisticated systems. The strut itself is the load- bearing member in this assembly, with the spring and shock absorber merely performing their duty as oppose to actually holding the car up. In the picture here, you can't see the shock absorber because it is encased in the black gaiter inside the spring.

The steering gear is either connected directly to the lower shock absorber housing, or to an arm from the front or back of the spindle (in this case). When you steer, it physically twists the strut and shock absorber housing (and consequently the spring) to turn the wheel. The spring is seated in a special plate at the top of the assembly which allows this twisting to take place. If the spring or this plate are worn, you'll get a loud 'clonk' on full lock as the spring frees up and jumps into place. This is sometimes confused with CV joint knock. Double wishbone suspension systems The following three examples are all variations on the same theme.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 121 Coil spring type 1 This is a type of double-A or double wishbone suspension. The wheel spindles are supported by an upper and lower 'A' shaped arm. In this type, the lower arm carries most of the load. If you look head-on at this type of system, what you'll find is that it's a very parallelogram system that allows the spindles to travel vertically up and down. When they do this, they also have a slight side-to-side motion caused by the arc that the wishbones describe around their pivot points.

This side-to-side motion is known as scrub. Unless the links are infinitely long the scrub motion is always present. There are two other types of motion of the wheel relative to the body when the suspension articulates. The first and most important is a toe angle (steer angle).

The second and least important, is the , or lean angle. Steer and camber are the ones which wear tyres.

Coil spring type 2 This is also a type of double-A arm suspension although the lower arm in these systems can sometimes be replaced with a single solid arm (as in the picture). The only real difference between this and the previous system mentioned above is that the spring/shock combo is moved from between the arms to above the upper arm.

This transfers the load-bearing capability of the suspension almost entirely to the upper arm and the spring mounts. The lower arm in this instance becomes a control arm. This particular type of system isn't very popular in cars as it takes up a lot of room.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 122 Multi-link suspension This is the latest variation of the double wishbone system described above. The basic principle of it is the same, but instead of solid upper and lower wishbones, each 'arm' of the wishbone is a separate item.

These are joined at the top and bottom of the spindle thus forming the wishbone shape. The weird thing about this is that as the spindle turns for steering, it alters the geometry of the suspension by torquing all four suspension arms. They have complex pivot systems designed to allow this to happen.

Car manufacturers claim that this system gives even better road- holding properties, because all the various joints make the suspension almost infinitely adjustable.

There are a lot of variations on this theme, with huge differences in the numbers and complexities of joints, numbers of arms, positioning of the parts etc. But they are all fundamentally the same. Note that in this system the spring is separate from the shock absorber.

Trailing-arm suspension The trailing arm system is literally that - a shaped suspension arm is joined at the front to the chassis, allowing the rear to swing up and down. Pairs of these become twin- trailing-arm systems and work on exactly the same principle as the double wishbones in the systems described above. The difference is that instead of the arms sticking out from the side of the chassis, they travel back parallel to it. This is an older system not used so much any more because of the space it takes up, but it doesn't suffer from the side-to-side scrubbing problem of double wishbone systems.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 123 Twin I-beam suspension Used almost exclusively by Ford F- series trucks, twin I-beam suspension was introduced in 1965. This little oddity is a combination of trailing arm suspension and solid beam axle suspension. However, in this case the beam is split in two and mounted offset from the centre of the chassis, one section for each side of the suspension.

The trailing arms are actually (technically) leading arms and the steering gear is mounted in front of the suspension setup. Ford claim this makes for a heavy-duty independent front suspension setup capable of handling the loads associated with their trucks. In an empty truck, however, going over a bump with twin I-beam suspension gives an extremely bumpy ride.

Moulton rubber suspension This suspension system is based on the compression of a solid mass of rubber - red in both these images. The two types are essentially derivatives of the same design. It is named after Dr. Alex Moulton - one of the original design team on the Mini, and the engineer who designed its suspension system in 1959.

Transverse leaf-spring This system is a bit odd in that it combines independent double wishbone suspension with a like you'd normally find on the rear suspension. Famously used on the Corvette, it involves one leaf spring mounted across the vehicle, connected at each end to the lower wishbone.

The centre of the spring is connected to the front subframe in the middle of the car. There are still two shock absorbers, mounted one to each side on the lower wishbones. This type of system is very rare.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 124 Rear suspension - dependent (linked) systems

Solid-axle, leaf-spring This system was favoured by the Americans for years because it was very simple and cheap to build. The ride quality is decidedly questionable though. The drive axle is clamped to the leaf springs and the shock absorbers normally bolt directly to the axle. The ends of the leaf springs are attached directly to the chassis, as are the tops of the shock absorbers. Simple, not particularly elegant, but cheap. The main drawback with this arrangement is the lack of lateral location for the axle, meaning it has a lot of side-to-side slop in it.

Solid-axle, coil-spring This is a variation and update on the system described above. The basic idea is the same, but the leaf springs have been removed in favour of either 'coil-over-oil' spring and shock combos, or as shown here, separate coil springs and shock absorbers. Because the leaf springs have been removed, the axle now needs to have lateral support from a pair control arms.

The front ends of these are attached to the chassis, and the rear ends to the axle. The variation shown here is more compact than the coil- over-oil type, and it means you can have smaller or shorter springs. This in turn allows the system to fit in a smaller area under the car.

Beam axle This system is used in front wheel drive cars, where the rear axle isn't driven. (Hence its full description as a "dead beam"). Again, it is a relatively simple system. The beam runs across under the car with the wheels attached to either end of it. Spring / shock units or struts are bolted to either end and are placed up into suspension wells in the car body or chassis.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 125 The beam has two integral trailing arms built in instead of the separate control arms required by the solid-axle coil-spring system. Variations on this system can have either separate springs and shocks, or the combined 'coil-over-oil' variety as shown here. One notable feature of this system is the track bar (or ). This is a diagonal bar which runs from one end the beam to a point either just in front of the opposite control arm (as here) or sometimes diagonally up to the top of the opposite spring mount (which takes up more room).

This is to prevent side-to-side movement in the beam which would cause all manner of nasty handling problems. A variation on these is the twist axle which is identical with the exception of the panhard rod. In a twist axle, the axle is designed to twist slightly. This gives, in effect, a semi-independent system whereby a bump on one wheel is partially soaked up by the twisting action of the beam.

Yet another variation on this system does away with the springs and replaces them with torsion bars running across the chassis, and attached to the leading edge of the control arms. These beam types are currently very popular because of their simplicity and low cost.

4-bar 4-bar suspension can be used on the front and rear of vehicles – it is shown in the "rear" section of this page because that's where it's normally found. 4-bar suspension comes in two varieties. Triangulated,

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 126 shown on the left here, and parallel, shown on the right.

The parallel design operates on the principle of a "constant motion parallelogram". The design of the 4-bar is such that the rear end housing is always parallel to the ground, and the pinion angle never changes.

This, combined with the lateral stability of the Panhard Bar, does an excellent job of locating the rear end and keeping it in proper alignment. If you were to compare this suspension system on a truck with a 4-link or ladder-bar setup, you'd notice that the rear frame "kick up" of the 4- bar setup is far less severe. This, combined with the relatively compact installation design means that it's ideal for cars and trucks where space is at a premium.

The triangulated design operates on the same principle, but the top two bars are skewed inwards and joined to the rear end housing much closer to the centre. This eliminates the need for the separate panhard bar, which in turn means the whole setup is even more compact.

Derivatives of the 4-bar system There are many variations on the 4-bar systems illustrated above. For example, if the four angled bars go from the axle outboard to the chassis near the centreline, this is called a "Satchell link". (Satchell is a US designer, who used the above linkage on some of Paul Newman’s Datsun road racers some years back.)

It has certain advantages over the above examples. Both of these angled linkages can be reversed to have the angled links below the axle and the parallel links above. The roll centre will be lowered with the angled bars under the axle, a function which is difficult to accomplish without this design.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 127 De Dion suspension, or the de Dion tube The de Dion tube is a semi- independent rear suspension system designed to combat the twin evils of unsprung weight and poor ride quality in live axle systems. De Dion suspension is a strange mixture of live-axle solid-beam suspension and fully independent trailing-arm suspension.

It's neither one, but at the same time it's both. With this system, the wheels are interconnected by a de Dion Tube, which is essentially a laterally-telescoping part of the suspension designed to allow the wheel track to vary during suspension movement.

This is necessary because the wheels are always kept parallel to each other, and thus perpendicular to the road surface regardless of what the car body is doing. This setup means that when the wheels rebound, there is also no camber change which is great for traction, and that's the first advantage of a de Dion Tube. The second advantage is that it contributes to reduced unsprung weight in the vehicle because the transfer case / differential is attached to the chassis of the car rather than the suspension itself.

Naturally, the advantages are equalled by disadvantages, and in the case of de Dion systems, the disadvantages would seem to win out. Firstly, it needs two CV joints per axle instead of only one. That adds complexity and weight. Because one of the advantages of not having the differential as part of the suspension is a reduction in weight, adding more weight back into the system to compensate for the design is a definite disadvantage.

Secondly, the brakes are mounted inboard with the calipers attached to the transfer case, which means to change a brake disc, you need to dismantle the entire suspension system to get the driveshaft out.

Finally, de Dion units can be used with a leaf-spring or coil-spring arrangement. With coil spring (as shown here) it needs extra lateral

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 128 location links, such as a panhard rod, wishbones or trailing links. Again - more weight and complexity.

Rear suspension - independent systems It follows, that what can be fitted to the front of a car, can be fitted to the rear to without the complexities of the steering gear. Simplified versions of all the independent systems described above can be found on the rear axles of cars.

The multi-link system is currently becoming more and more popular. In advertising, it's put across as '4-wheel independent suspension'. This means all the wheels are independently mounted and sprung. There are two schools of thought as to whether this system is better or worse for handling than, for example, Macpherson struts and a twist axle. The drive towards 4-wheel independent suspension is primarily to improve ride quality without degrading handling.

Hydrolastic suspension Hydrolastic suspension is a system in which the front and rear suspension systems are connected together in order to better level the car when driving.

The principle is simple. The front and rear suspension units have Hydrolastic displacers, one per side. These are interconnected by a small pipe. Each displacer incorporates a rubber spring (as in the Moulton rubber suspension system), and damping of the system is achieved by rubber valves.

But what happens when the front and rear wheels encounter bumps or dips together? One cannot take precedent over the other, so the fluid suspension stiffens in response to the combined upward motion and, while acting as a damper, transfers the load to the rubber springs instead, giving a controlled, vertical, but level motion to the car.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 129

Remember the units were connected with a small bore pipe? The restriction of the fluid flow, imposed by this pipe, rises with the speed of the car. This means a steadier ride at high speed, and a softer more comfortable ride at low speed.

Hydrolastic suspension is hermetically sealed and thus shouldn't require much, if any, attention or maintenance during its normal working life. Bear in mind that hydrolastic suspension was introduced in 1964, and you'd be lucky to find a unit today that has had any work done to it.

The image here shows a typical lateral installation for hydrolastic rear suspension.

The suspension swing arms are attached to the main sub frame. The red cylinders are the displacer units containing the fluid and the rubber spring. The pipes leading from the units can be seen and they would connect to the corresponding units at the front of the vehicle.

Hydrolastic suspension shouldn't be confused with Citroën's hydropneumatic suspension (see diagram). That system uses a hydraulic pump that raises and lowers the car to different heights. It is certainly a superior system but it's also a lot more costly to manufacture and maintain. That's due in part to the fact that they don't use o-rings as seals; the pistons and bores are machined to incredible tolerances (microns), that it makes seals unnecessary. The disadvantage is that if something leaks, you need a whole new cylinder assembly.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 130 Hydropneumatic suspension

Since the early fifties, Citroën have been running a fundamentally different system to the rest of the auto industry. It’s called hydro- pneumatic suspension, and it is a whole-car solution which can include the brakes and steering as well as the suspension itself.

The core technology of hydro-pneumatic suspension is (as you might guess from the name) hydraulics. Ultra-smooth suspension is provided by the fluid's interaction with a pressurised gas, and in this respect, it’s very similar to the hydragas system described above.

Citroën pioneered the system in the rear suspension of the 15 (Traction Avant) model, and it has been fitted to many of their cars since.

The system is powered by a large hydraulic pump, typically belt-driven by the engine like an or an air conditioner. the pump provides fluid to an accumulator at pressure, where it is stored ready to be delivered to serve a system.

This pump may also be used for the power steering and the brakes, and in the DS for the semi-automatic gearbox.

Note - the C5 and C6 only use the high pressure hydraulics for the suspension - brakes and steering are conventional.

The spring in this suspension system is provided by a hydraulic component called a suspension sphere. The accumulator is an

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 131 additional sphere (which holds a reserve of hydraulic fluid under pressure to even out the load on the pump caused by varying demand) acting rather like a battery.

The accumulator is gas (typically nitrogen) under pressure in a bottle contained within a diaphragm. This is effectively a balloon which allows pressurised fluid to compress the gas, and then as pressure drops the gas pushes the fluid back to keep the system's pressure up. In the image here, the nitrogen gas is represented in red and the LHM fluid is represented in green. As the pressure in the fluid overcomes the gas pressure, the nitrogen is compressed by the diaphragm being pushed back. Then as the pressure in the fluid reduces, the gas pushes back the diaphragm which expels the fluid from the sphere, returning gas and fluid to equilibrium. This is the hydro-pneumatic equivalent to the spring being compressed and then rebounding.

It is important that you understand where the fluid acting on the diaphragm in the sphere gets its force from, and to do that we are going to have to look at the operation of the other key component in the Citroën system - the strut.

The sphere in these systems is actually mounted at the end of the strut. The strut itself acts like a syringe to inject fluid into the sphere. When the wheel hits a bump it rises, pushes the piston back and this squeezes fluid through the tiny hole in the sphere to let the gas spring absorb the energy of the bump. Then when the car is over the bump, the gas pushes the diaphragm back out, pushing the fluid down to the strut, pushing the wheel down to the ground. In the "hard mode", again selected dynamically by the computer based on inputs such as steering wheel angle and road speed, the central unit is isolated, completely blocking the cross-flow of oil and isolating the middle sphere, giving stiffer springing, much stiffer damping, and much reduced body roll.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 132 Digital suspension systems

Beginning in 2006 with the Audi TT the concept of fully independent suspension systems came into being. Traditional 'analogue' independent suspension is still connected side-to-side by anti-roll bars. With the advent of computer-controlled suspension systems that are able to rapidly adapt to changing road surfaces, the anti-roll bar is no longer needed.

Its function can be replaced as long as sensors and electronically- adjustable suspension can be combined.

For example, when the sensors detect body roll in a corner, the suspension components in all four corners of the car can be electronically adjusted to compensate in real-time. Other vehicles that use digital suspension now are the Range Rover Evoque and the Audi R8 but the list will surely grow as it becomes more mainstream.

The next couple of topics deal with two such systems - ferrofluid, and linear electromagnetic suspension.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 133 Ferrofluid or magneto-rheological fluid dampers - Audi Magnetic Ride With the 2006 Audi TT, Audi launched their innovative magnetic semi- . It’s a totally new form of damping technology refined from Delphi's MagneRide system.

Magneride was designed to attempt to resolve the long-standing conflict between cabin comfort and driving dynamics. The Audi system is a continuously adaptive system - ie it's a closed feedback loop that can react to changes both in the road surface and the gear-changes (front-to-back weight shift) within milliseconds.

So how does this work? Well, the dampers in the Audi system are not filled with your regular old shock absorber oil, but with magneto- rheological fluid. This is a synthetic hydrocarbon oil containing sub- miniature magnetic particles.

When a voltage is applied to a coil inside the damper piston, it creates a magnetic field (remember the left- and right-handed electro-magnetic rules that make electric motors work). Inside the magnetic field, all the magnetic particles in the oil change alignment in microseconds to lie predominantly across the damper. Because the damper is trying to squeeze oil up and down through the flow channels, having the particles lined up transverse to this motion makes the oil 'stiffer'. Stiffer oil flows less, which stiffens up the suspension.

The Audi system has a centralised control unit which sends signals to the coils on each damper. Hooked up to complex force and acceleration sensing gauges, the control unit constantly analyses what's going on with the car and adjusts the damping settings accordingly. Because there are no moving parts - no valves to open or close - the system reacts within microseconds; far quicker than any other active suspension technology on the market today.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 134 And because the amount of voltage applied to the coils can be varied nearly infinitely, the dampers have a similarly near-infinite number of settings. The power usage for each strut is around 5 Watts, and the entire unit takes up no more room than a regular coil-over-oil unit.

The diagram here shows the basic principle of magnetised vs. unmagnetised ferrofluid, as well as a cutaway of the piston assembly in a Magneride-type damper. The little blue balls represent the particles of fluid; they have been greatly enlarged in the picture, so you can see them.

Air suspension In days gone by, air suspension was limited to expensive logistics trucks - heavy goods vehicles that needed to be able to maintain a level ride no matter what the road condition. Nowadays, you can retrofit air suspension to just about any vehicle you like from a Range Rover to a Ferrari.

Air suspension replaces the springs in your car with either an air bag or an air strut made of high-tensile super flexible polyurethane rubber. Each air bag or strut is connected to a valve to control the amount of air allowed into it.

The valves are in turn connected to an air compressor and a small compressed air reservoir. By opening and closing the four valves, the amount of air sent to each unit can be varied.

By letting the same amount of air out of all the units, reducing the pressure in the bags, your car gets lowered, whilst increasing the air pressure by the same amount in each unit results in your car lifting higher off the ground. The rubber bags filled with air provide the springing action that used to be the realm of metal springs, and you have the option to maintain the factory (or aftermarket) shock absorbers.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 135 Why air suspension? Simple: ride quality. A well-set-up air suspension system can surpass metal spring suspension in just about any situation. If you want a luxurious, smooth, supple ride that will iron out the deepest of ruts and crevasses in the road, air suspension is what you're looking for. It's why logistics firms have used it in their trucks for so many years - air suspension transmits much less road vibration into the vehicle chassis.

Bags and struts Air bag systems come in two different types - air bags and air struts.

The bags are typically used for leaf-spring suspension vehicles, but can easily be adapted (through the use of bolt-on brackets) to almost any swinging-arm type suspension system. Air bags are the most reliable systems because of their simplicity.

Air struts are a little more complex and come in two flavours - simple struts and pivoting struts. It used to be that you could only have a simple strut because none of the manufacturers had worked out how to keep the air strut sealed when it twisted - a function that is required if you're going to replace a MacPherson strut. Now though, there are a couple of different options for MacPherson strut replacement, the most complex being the twisting double-doughnut style strut that still allows the shock absorber to pass through the middle of it.

The two images above show an air bag system as applied to the rear leaf spring suspension on a truck, and a simple non-twisting air strut system as applied to a double swing-arm unit.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 136 Ride height sensors Most systems are far more sophisticated than simple air suspension. For example, each unit will normally work in conjunction with a ride- height sensor. This is a mechanical lever linked to the suspension arm at one end, and to an electronic resistance pot at the other. The pot is connected to the chassis or frame so that the lever spins the pot as the suspension moves up and down. A computer can use this to read the height of the vehicle in that corner, and with that data, all sorts of wonderful things can happen.

For example, if you press down hard on the accelerator pedal, a car will typically squat under acceleration. When this happens, the ride height at the rear of the car gets less. An air suspension system can register this and either send more air to the rear, or reduce the pressure at the front to level off the car again. Same goes for side-to-side roll in corners - air suspension can compensate somewhat for body roll when connected to ride-height sensors. New generation systems also incorporate air pressure sensors to add another level of feedback to the system.

Control panels In a factory-fit air suspension system, the control panel will either be integrated into the onboard computer (like BMW's i-Drive), or be accessible via a ride-height adjustment control. The control panel is how you determine what you want the suspension to do, be it low down for sporty driving, or high off the ground for extra clearance.

Anti-roll bars (sway bars/stabilizers)

These aren't the things that are bolted inside the car in case you turn it over - those are rollover cages. Anti-roll bars do precisely what their name implies - they combat the roll of a car on its suspension as it corners. They're also known as sway-bars or anti-sway-bars.

Almost all cars have them fitted as standard. From the factory they are biased towards ride comfort. Stiffer aftermarket items will increase the road-holding but you'll get reduced comfort because of it. Fiddling with your roll stiffness distribution can make a car uncomfortable to ride in and extremely hard to handle if you get it wrong.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 137

The anti-roll bar is usually connected to the front, lower edge of the bottom suspension joint. It passes through two pivot points under the chassis, usually on the sub frame and is attached to the same point on the opposite suspension setup.

Effectively, it joins the bottom of the suspension parts together. When you head into a corner, the car begins to roll out of the corner. For example, if you're cornering to the left, the car body rolls to the right. In doing this, it's compressing the suspension on the right hand side.

With a good anti-roll bar, as the lower part of the suspension moves upward relative to the car chassis, it transfers some of that movement to the same component on the other side. In effect, it tries to lift the left suspension component by the same amount. Because this isn't physically possible, the left suspension effectively becomes a fixed point and the anti-roll bar twists along its length because the other end is effectively anchored in place. It's this twisting that provides the resistance to the suspension movement.

Note: with the advent of digital suspension systems, anti-roll bars are starting to be phased out on some vehicles as they can be replaced with quick-reacting electronically-controlled suspension components.

Suspension bushes

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 138 These are the rubber grommets which separate most of the parts of your suspension from each other. They're used at the link of an A-Arm with the sub-frame. They're used on anti-roll bar links and mountings. They're made of rubber. Rubber doesn't last.

Replace them with polyurethane or polygraphite bushes - they are hard-wearing and last a great deal longer. Like all suspension-related items though, bushes are a trade-off between performance and comfort. The harder the bush compound, the less comfort in the cabin.

Sprung vs. unsprung weight Simply put, sprung weight is everything from the springs up, and unsprung weight is everything from the springs down. Wheels, shock absorbers, springs, knuckle joints and tyres contribute to the unsprung weight. The car, engine, fluids, you, your passenger, the kids, all contribute to the sprung weight.

Reducing unsprung weight is the key to increasing performance of the car. If you can make the wheels, tyres and swing-arms lighter, then the suspension will spend more time compensating for bumps in the road, and less time compensating for the mass of the wheels etc.

The greater the unsprung weight, the greater the inertia of the suspension, which will be unable to respond as quickly to rapid changes in the road surface As an added benefit, putting lighter wheels on the car can increase your engine's apparent power. This is because the engine has to turn the gearbox and driveshafts, and at the end of that, the wheels and tyres.

Heavier wheels and tyres require more torque to get turning, which saps engine power. Lighter wheels and tyres allow more of the engine's torque to go into getting you going than into spinning the wheels. That's why sports cars have carbon fibre driveshafts and ultra light alloy wheels.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 139 Progressively wound springs These are the things to go for when you upgrade your springs. In fact, it's difficult not to get progressive springs when you upgrade - most of the aftermarket manufacturers make them like this. Most factory springs are normally wound. That is to say that their coil pitch stays the same all the way up the spring. If you get progressively wound springs, the coil pitch gets tighter the closer to the top of the spring you get. This has the effect of giving the spring increasing resistance, the more it is compressed.

The spring constant (stiffness) of a coil spring equals: k = compression / force = D^4 * G / (64*N*R^3)where D is the wire diameter, G an elastic material property, N the number of coils in the spring, and R the radius of the spring.

So increasing the number of coils decreases the stiffness of the spring. Thus, a progressive spring is progressive because the two parts are compressed equally until the tightly wound part locks up, effectively shortening the spring and reducing its compliance.

So for normal driving, you'll be using mostly the upper 3 or 4 'tight' winds to soak up the average bumps and potholes. When you get into harder driving, like cornering at speed for example, because the springs are being compressed more, they resist more.

The effect is to reduce the suspension travel at the top end resulting in less body roll, and better road-holding. Invariably, the fact that the springs are progressively wound is what accounts for the lowering factor. The springs aren't made shorter - they're just wound differently.

Torsion bars Torsion bars (or torsion rods) deserve their own section because they are a

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 140 type of spring which can be used in place of coil- or leaf-springs. A torsion bar is a solid bar of steel which is connected to the car chassis at one end, and is free to move at the other end. They can be mounted across the car (transverse like the rear suspension on the Peugeot 205 and Renault 16) or along the car (longitudinal, like the front suspension on the Morris Minor) - one for each side of the suspension.

The springing motion is provided by the metal bar's resistance to twisting. To over-simplify, stick your arm out straight and get someone to twist your wrist. Presuming that your friend doesn't snap your wrist, at a certain point, resistance in your arm (and pain) will cause you to twist your wrist back the other way. That is the principle of a torsion bar.

Torsion bars are normally locked to the chassis and the suspension parts with splined ends. This allows them to be removed, twisted round a few splines and re-inserted, which can be used to raise or lower a car, or to compensate for the natural 'sag' of a suspension system over time.

They can be connected to almost any type of suspension system listed earlier. The drawing on the previous page shows an example longitudinal torsion bar. The small lever at the far end of the torsion bar would be attached solidly to the frame to provide the fixed end. The torsion bar itself fits into that lever and the suspension arm at the front through splined holes. As the suspension at the front moves upwards, the bar twists along its length providing the springing motion. The shock absorber assembly has been left out of this drawing for clarity.

Most vehicles now don't use 'pure' Ackermann steering geometry because it doesn't take some of the dynamic and compliant effects

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 141 of steering and suspension into account, but some derivative of this is used in almost all steering systems.

STEERING SECTION back to ToC Basic steering components 99% of the world's car steering systems are made up of the same three or four components: the steering wheel, which connects to the steering system, which connects to the track rod, which connects to the tie rods, which connect to the steering arms.

The steering system can be one of several designs, which be discussed later, but all the designs essentially move the track rod left- to-right across the car. The tie rods connect to the ends of the track rod with ball and socket joints, and then to the ends of the steering arms, also with ball and socket joints.

The purpose of the tie rods is to allow suspension movement as well as an element of adjustability in the steering geometry. The tie rod lengths can normally be changed to achieve these different geometries.

The Ackermann Angle : your wheels don't point the same direction

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 142 When a car goes around a corner, the outside wheels travel further than the inside wheels. In the case of a transmission, it's why you need a differential (see the Transmission Section), but in the case of steering, it's why you need the front wheels to point in different directions. On the right is the diagram from the Transmission Section. You can see the inside wheels travel around a circle with a smaller radius (r2) than the outside wheels (r1).

In order for that to happen without causing undue stress to the front wheels and tyres, they must point at slightly different angles to the centreline of the car. The diagram on the right shows the same thing only zoomed in to show the relative angles of the tyres to the car. It's all to do with the geometry of circles.

This difference of angle is achieved with a relatively simple arrangement of steering components to create a trapezoid geometry (a parallelogram with one of the parallel sides shorter than the other). Once this is achieved, the wheels point at different angles as the steering geometry is moved.

Why 'Ackermann'? This particular technology was first introduced in 1758 by Erasmus Darwin, father of Charles Darwin, in a paper entitled "Erasmus Darwin's improved design for steering carriages--and cars". It was never patented though until 1817 when Rudolph Ackermann patented it in London, and that's the name that stuck.

Steering ratios Every vehicle has a steering ratio inherent in the design. If it didn't you'd never be able to turn the wheels. Steering ratio gives mechanical advantage to the driver, allowing you to turn the tyres with the weight of the whole car sitting on them, but more importantly, it means you

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 143 don't have to turn the steering wheel a ridiculous number of times to get the wheels to move.

Steering ratio is the ratio of the number of degrees turned at the steering wheel vs. the number of degrees the front wheels are deflected. So for example, if you turn the steering wheel 20° and the front wheels only turn 1°, that gives a steering ratio of 20:1.

For most modern cars, the steering ratio is between 12:1 and 20:1. This, coupled with the maximum angle of deflection of the wheels, gives the lock-to-lock turns for the steering wheel.

For example, if a car has a steering ratio of 18:1 and the front wheels have a maximum deflection of 25°, then at 25°, the steering wheel has turned 25°x18, which is 450°. That's only to one side, so the entire steering goes from -25° to plus 25° giving a lock-to-lock angle at the steering wheel of 900°, or 2.5 turns (900° / 360).

This works the other way around too of course. If you know the lock-to- lock turns and the steering ratio, you can figure out the wheel deflection. For example, if a car is advertised as having a 16:1 steering ratio and 3 turns lock-to-lock, then the steering wheel can turn 1.5x360° (540°) each way. At a ratio of 16:1 that means the front wheels deflect by 33.75° each way.

For racing cars, the steering ratio is normally much smaller than for passenger cars - ie. closer to 1:1 - as racing drivers need to get fuller deflection into the steering as quickly as possible.

Turning circles The turning circle of a car is the diameter of the circle described by the outside wheels when turning on full lock. There is no hard and fast formula to calculate the turning circle but you can get close by using this:

The numbers required to calculate the turning circle explain why a classic black London taxi has a tiny 8m turning circle to allow it to do U- turns in the narrow London streets. In this case, the and Turning circle radius = (track/2) + track aren't radically different to any (wheelbase/sin(average steer angle)) other car, but the average steering

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 144 angle is huge. For comparison, a typical passenger car turning circle is normally between 11m and 13m with SUV turning circles going out as much as 15m to 17m.

Steering system designs: Pitman arm types There really are only two basic categories of steering system today; those that have pitman arms with a steering 'box' and those that don't. Older cars and some current trucks use pitman arms, so for the sake of completeness, some common types are included in this text. Newer cars and uni-body light-duty trucks typically all use some derivative of rack and pinion steering. Pitman arm mechanisms have a steering 'box' where the shaft from the steering wheel comes in and a lever arm comes out - the pitman arm. This pitman arm is linked to the track rod or centre link, which is supported by idler arms. The tie rods connect to the track rod

. There are a large number of variations of the actual mechanical linkage from direct-link where the pitman arm is connected directly to the track rod, to compound linkages where it is connected to one end of the steering system or the track rod via other rods.

The example above shows a compound link.

Most of the steering box mechanisms that drive the pitman arm have a 'dead spot' in the centre of the steering where you can turn the steering wheel a slight amount before the front wheels start to turn. This slack

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 145 can normally be adjusted with a screw mechanism but it can't ever be eliminated.

The traditional advantage of these systems is that they give bigger mechanical advantage and thus work well on heavier vehicles. With the advent of power steering, that has become redundant and the steering system design is now more to do with mechanical design, price and weight.

The following are the four basic types of steering box used in pitman arm systems.

Worm and sector In this type of steering box, the end of the shaft from the steering wheel has a worm gear attached to it. It meshes directly with a sector gear (so called because it's a section of a full gear wheel).

When the steering wheel is turned, the shaft turns the worm gear, and the sector gear pivots around its axis as its teeth are moved along the worm gear. The sector gear is mounted on the cross shaft which passes through the steering box and out the bottom where it is splined, and the pitman arm is attached to the splines.

When the sector gear turns, it turns the cross shaft, which turns the pitman arm, giving the output motion that is fed into the mechanical linkage on the track rod. The diagram shows the active components that are present inside the worm and sector steering box. The box itself is sealed and filled with grease.

Worm and roller The worm and roller steering box is similar in design to the worm and sector box. The difference here is that instead of having a sector gear that meshes with the worm gear, there is a roller instead. The roller is mounted on a roller bearing shaft and is held captive on the end of the cross shaft.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 146 As the worm gear turns, the roller is forced to move along it but because it is held captive on the cross shaft, it twists the cross shaft. Typically in these designs, the worm gear is actually an hourglass shape so that it is wider at the ends. Without the hourglass shape, the roller might disengage from it at the extent of its travel.

Worm and nut or recirculating ball This is by far the most common type of steering box for pitman arm systems. In a recirculating ball steering box, the worm drive has many more turns on it with a finer pitch.

A box or nut is clamped over the worm drive that contains dozens of ball bearings. These loop around the worm drive and then out into a recirculating channel within the nut where they are fed back into the worm drive again. That is why they are called “recirculating”.

As the steering wheel is turned, the worm drive turns and forces the ball bearings to press against the channel inside the nut. This forces the nut to move along the worm drive. The nut itself has a couple of gear teeth cast into the outside of it and these mesh with the teeth on a sector gear which is attached to the cross shaft just like in the worm and sector mechanism. This system has much less free play or slack in it than the other designs, and is the most popular type of system.

The drawing shows a recirculating ball mechanism with the nut shown in cutaway so you can see the ball bearings and the recirculation channel.

Cam and lever Cam and lever steering boxes are very similar to worm and sector steering boxes. The worm drive is known as a cam and has a much shallower pitch and the sector gear is replaced with two studs that sit in the cam channels.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 147

As the worm gear is turned, the studs slide along the cam channels which force the cross shaft to rotate, turning the pitman arm. One of the design features of this style is that it turns the cross shaft 90° to the normal so it exits through the side of the steering box instead of the bottom. This can result in a very compact design when necessary.

Steering system designs: Rack and pinion

This is by far the most common type of steering you'll find in any car today due to its relative simplicity and low cost. Rack and pinion systems give a much better feel for the driver, and there isn't the slop or slack associated with steering box pitman arm type systems.

The disadvantage is that unlike those systems, rack and pinion designs have no adjustability in them, so once they wear beyond a certain mechanical tolerance, they need to be completely replaced.

This is rare though. In a rack and pinion system, the track rod is replaced with the steering rack which is a long, toothed bar with the tie rods attached to each end. On the end of the steering shaft there is a simple pinion gear that meshes with the rack.

When you turn the steering wheel, the pinion gear turns, and moves the rack from left to right. Changing the size of the pinion gear alters the steering ratio. It really is that simple!

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 148

Variable-ratio rack and pinion steering This is a simple variation on the above design. All the components are the same, and it all works the same except that the spacing of the teeth on the rack varies depending on how close to the centre of the rack they are.

In the middle, the teeth are spaced close together to give slight steering for the first part of the turn - good for not oversteering at speed. As the teeth get further away from the centre, they increase in spacing slightly so that the wheels turn more for the same turn of the steering wheel towards full lock.

Vehicle dynamics and steering - how it can all go very wrong Generally speaking, when you turn the steering wheel in your car, you expect it to go where you're pointing it. At slow speed, this will almost always be the case but once you get some momentum behind you, you are at the mercy of the chassis and suspension designers. In racing, the aerodynamic wings, air splitters and under-trays help to maintain an even balance of the vehicle in corners along with the position of the weight in the vehicle and the suspension setup. The two most common problems you'll run into are .

Understeer Understeer is so called because the car steers less than you want it to. Understeer can be brought on by all manner of chassis, suspension and speed issues but essentially it means that the car is losing grip on the front wheels. Typically it happens as you brake and the weight is transferred to the front of the car.

At this point the mechanical grip of the front tyres can simply be overpowered and they start to lose grip (for example on a wet or greasy road surface). The end result is that the car will start to take the corner very wide. In racing, that normally involves going off the outside of the corner into a catch area or on to the grass. In normal driving, it means crashing at the outside of the corner. Getting out of understeer can involve letting off the throttle in front-wheel-drive vehicles (to try to

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 149 give the tyres chance to grip) or getting on the throttle in rear-wheel- drive vehicles (to try to bring the back end around).

Oversteer You will probably already have guessed that oversteer is the opposite of understeer. With oversteer, the car goes where it's pointed far too efficiently and you end up diving into the corner much more quickly than you had expected.

Oversteer is brought on by the car losing grip on the rear wheels as the weight is transferred off them under braking, resulting in the rear kicking out in the corner. Without counter-steering the end result in racing is that the car will spin and end up going off the inside of the corner backwards. In normal driving, it means spinning the car and ending up pointing back the way you came.

Counter-steering Counter-steering is what you need to do when you start to experience oversteer. If you get into a situation where the back end of the car loses grip and starts to swing out, steering opposite to the direction of the corner can often 'catch' the oversteer by directing the nose of the car out of the corner.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 150

TYRES & WHEELS SECTION back to ToC How to read your tyre markings Most of the information in a tyre marking is surplus to what you need to know. So here are the important details:

Key Tyre Marking Description A Manufacturers or brand name, and commercial name or identity. Tyre size, construction and speed rating designations. Tubeless designates a tyre which requires no inner tube. See tyre sizes and B speed ratings below. DIN-type tyre marking also has the load index encoded in it. These go from a load index of 50 (190kg) up to an index of 169 (5800kg). C Denotes type of car tyre construction. M&S denotes a car tyre designed for mud and snow. Reinforced D marking only where applicable. E Pressure marking requirement. F ECE (not EEC) type approval mark and number. North American Dept of Transport compliance symbols and G identification numbers. H Country of manufacture.

As well as all that, you might also find the following embossed in the rubber tyre marking:

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 151

 The temperature rating - an indicator of how well the tyre withstands heat build-up. "A" is the highest rating; "C" is the lowest.  The traction rating - an indicator of how well the tyre is capable of stopping on wet pavement. "AA" is the highest rating; "C" is the lowest.  The tread-wear rating - a comparative rating for the useful life of the tyre's tread. A tyre with a tread-wear rating of 200, for example, could be expected to last twice as long as one with a rating of 100. Tread-wear grades typically range between 60 and 600 in 20-point increments. It is important to consider that this is a relative indicator, and the actual life of a tyre's tread will be affected by quality of road surfaces, type of driving, correct tyre inflation, proper and other variable factors. In other words, don't think that a tread-wear rating of 100 means a 30,000 mile tyre.

Encoded in the US DOT information (G in the tyre marking above) is a two-letter code that identifies where the tyre was manufactured in detail. In other words, what factory and in some cases, what city it was manufactured in. It's the first two letters after the 'DOT' - in this case "FA" denoting Yokohama.

OE manufacturer letters In the same way that Porsche specifies N-rated tyres (see later), there are even more markings on the sidewall of a tyre that can denote tyres fitted as original equipment (OE) to various makes of vehicle. In some cases, the 'preferred' OE tyres are slightly different than the same- named tyres without the OE specification.

DOT codes and the 6-year shelf life As part of the DOT code (G in the tyre marking above), there is a tyre manufacture date stamped on the sidewall. Oddly this code is sometimes only on one sidewall so you might need to get under your car and look at the inward-facing side of the tyre.

Take a look at yours - there will be a three- or four-digit code. This code denotes when the tyre was manufactured, and as a rule-of- thumb, you should never use tyres more than 6 years old. The rubber

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 152 in tyres degrades over time, irrespective of whether the tyre is being used or not.

Reading the code. The code is pretty simple. The three-digit code was used for tyres manufactured before 2000. So for example 1 7 6 means it was manufactured in the 17th week of 6th year of the decade.

In this case it means 1986. For tyres manufactured in the 90's, the same code holds true but there is a little triangle after the DOT code. So for this example, a tyre manufactured in the 17th week of 1996 would have the code 176

After 2000, the code was switched to a 4-digit code. Same rules apply, so for example 3 0 0 3 means the tyre was manufactured in the 30th week of 2003.

The E-mark Item F in the tyre marking diagram above is the E-mark. All tyres sold in Europe after July 1997 must carry an E- mark. The mark itself is either an upper or lower case "E" followed by a number in a circle or rectangle, followed by a further number.

An "E" (upper case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30.

An "e" (lower case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of Directive 92/33/EEC.

The number in the circle or rectangle denotes the country code of the government that granted the type approval. 11 is the UK. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tyre size and type.

Tyre size notations What do the size notations mean? Tyre size markings:

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 153

This is the width This is the ratio of the in mm of the tyre This tells you height of the tyre from sidewall to that the tyre is a This is the diameter in sidewall, (section sidewall when radial inches of the rim of the height), expressed as a This is the it's unstressed construction. wheel that the tyre has percentage of the speed and you're Look at tyre been designed to fit width. It is known as rating of looking at it head construction if on. Beware! Tyre sizes the aspect ratio. In this the tyre. on (or top-down). you want to mix imperial and case, 65% of 185mm is This is known as know what that metric measurements. 120.25mm - the section the section means. height. width.

More recently, there has been a move (especially in Europe) to adjust tyre designations to conform to DIN. This is the German Institute for standardisation – Deutsches Institut fur Normung, often truncated to Deutsche Industrie Normal. DIN sizing means a slight change in the way the information is presented to the following:

Section Aspect Rim Load Radial Speed rating.

width ratio diameter index

Ultra high speed tyre size notations There is a subtle difference in the notation used on ultra high speed tyres, in particular motorcycle tyres. For the most part, the notation is the same as the DIN style described above. The difference is in the way the speed rating is displayed.

For these tyres, if the speed rating is above 149mph, then a 'Z' must appear in the dimension part of the notation, as well as the actual speed rating shown elsewhere. The 'Z' is a quick way to see that the tyre is rated for over 149mph.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 154

Section Aspect 149+ mph Rim Load Speed Radial

width ratio rated diameter index rating.

Speed ratings All tyres are rated with a speed letter. This indicates the maximum speed that the tyre can sustain for a ten minute endurance without coming to pieces and destroying itself – and your car.

Max Speed Max Speed Speed Capability Speed Capability Symbol Symbol Km/h MPH Km/h MPH L 120 75 S 180 113 M 130 81 T 190 118 N 140 87 U 200 125 P 150 95 H 210 130 Q 160 100 V 240 150 R 170 105 W 270 168 Y 300 186

Z 240+ 150+

'H' rated tyres are becoming the most commonplace and widely used tyres, replacing 'S' and 'T' ratings. Percentage-wise, the current split is something like this: S/T=67%, H=23%, V=8%. Certain performance cars come with 'V' or 'Z' rated tyres as standard, to match the performance capability of the car.

Load indices The load index on a tyre is a numerical code associated with the maximum load the tyre can carry. These are generally valid for speed under 210km/h (130mph). Once you get above these speeds, the load- carrying capacity of the tyre decreases. The table below gives you most of the Load Index (LI) values you're likely to come across.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 155 For the sake of simplicity, if you know your car weighs 2 tons - 2000kg - then assume an even weight on each wheel. 4 wheels at 2000kg = 500kg per wheel. This is a load index of 84. The engineer in you should add 10% or more for safety's sake. For this example, you could probably add 20% for a weight capacity of 600kg - a load index of 90. Generally speaking, the average car tyre is going to have a much higher load index than you'd ever need. It's better to have something that will fail at speeds and stress levels you physically can't achieve, than have something that will fail if you are travelling at normal speeds with a small load.

LI kg LI kg LI kg LI kg LI kg LI kg 50 190 70 335 90 600 110 1060 130 1900 150 3350 91 615 51 195 71 345 92 630 111 1090 131 1950 151 3450 52 200 72 355 93 650 112 1120 132 2000 152 3550 94 670 53 206 73 365 95 690 113 1150 133 2060 153 3650 54 212 74 375 96 710 114 1180 134 2120 154 3750

97 730 55 218 75 387 115 1215 135 2180 155 3875 98 750 56 224 76 400 116 1250 136 2240 156 4000 99 775 100 800 57 230 77 412 117 1285 137 2300 157 4125 101 825 58 236 78 425 118 1320 138 2360 158 4250 102 850 59 243 79 437 103 875 119 1360 139 2430 159 4375 60 250 80 450 104 900 120 1400 140 2500 160 4500 105 925 61 257 81 462 106 950 121 1450 141 2575 161 4625 62 265 82 475 107 975 122 1500 142 2650 162 4750 108 1000 63 272 83 487 123 1550 143 2725 163 4875 64 280 84 500 109 1030 124 1600 144 2800 164 5000

65 290 85 515 125 1650 145 2900 165 5150 66 300 86 530 126 1700 146 3000 166 5300

67 307 87 545 127 1750 147 3075 167 5450 68 315 88 560 128 1800 148 3150 168 5600

69 325 89 580 129 1850 149 3250 169 5800

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 156 Car tyre types

There are several different types of car tyre that you can buy for your car. What you choose depends on how you use your car, where you live, how you like the ride of your car and a variety of other factors. The different classifications are as follows, and some representative examples are shown in the image above.

Performance tyres or summer tyres Performance tyres are designed for faster cars or for people who prefer to drive harder than the average consumer. They typically put performance and grip ahead of longevity by using a softer rubber compound. Tread block design is normally biased towards outright grip rather than the ability to pump water out of the way on a wet road. The extreme example of performance tyres are "slicks" used in motor racing, so-called because they have no tread at all.

All-round or all-season tyres These tyres are what you'll typically find on every production car that comes out of a factory. They're designed to be a compromise between grip, performance, longevity, noise and wet-weather safety. For increased tyre life, they are made with a harder rubber compound, which sacrifices outright grip and cornering performance. For most drivers, this isn't an issue.

The tread block design is normally a compromise between quiet running and water dispersion - the tyre should not be too noisy in normal use but should work fairly well in downpours and on wet roads. All-season tyres are neither excellent dry-weather, nor excellent wet- weather tyres, but a compromise.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 157 Wet-weather tyres Rather than use an even harder rubber compound than all-season tyres, wet weather tyres actually use a softer compound than performance tyres. The rubber needs to heat up quicker in cold or wet conditions and needs to have as much mechanical grip as possible.

They'll normally also have a lot more sipping to try to disperse water from the . Aqua-channel tyres are a subset of winter or wet-weather tyres.

All-terrain tyres All-terrain tyres are typically used on SUVs and light trucks. They are larger tyres with stiffer sidewalls and bigger tread block patterns. The larger tread block means the tyres are very noisy on normal roads but grip loose sand and dirt very well when you take the car or truck off- road.

As well as the noise, the larger tread block pattern means less tyre surface in contact with the road. The rubber compound used in these tyres is normally neither soft nor hard.

Mud tyres At the extreme end of the all-terrain tyre classification are mud tyres. These have massive, super-chunky tread blocks and really shouldn't ever be driven anywhere other than loose mud and dirt. The tread sometimes doesn't even come in blocks any more but looks more like paddles built in to the tyre carcass.

Tyre constructions Almost all modern tyres are radial tyres. Radial tyres wear much better than cross-ply tyres and have a far greater rigidity for when cars are cornering and the tyres are deforming.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 158

Cross-ply components Radial components

The tread consists of specially compounded/vulcanised rubber which can have unique characteristics ranging from wear resistance, cut resistance, heat resistance, low rolling resistance, or any combination of these. The purpose of the tread is to transmit the forces between the rest of the tyre and the ground. The sidewall is a protective rubber coating on the outer sides of the tyre. It is designed to resist cutting, scuffing, weather checking, and cracking. The chafer of a radial tyre acts as a reinforcement. It increases the overall stiffness of the bead area, The chafer protects the bead and which in turn restricts deflection body from chafing (wear from and deformation and increases rubbing) where the tyre is in the durability of the bead area. It contact with the rim. also assists the bead in transforming the torque forces from the rim to the radial ply. The liner is an integral part of all tubeless pneumatic tyres. It covers the inside of the tyre from bead to bead and prevents the air from escaping through the tyre. The bead of a cross-ply tyre consists of bundles of bronze coated high tensile strength steel wire strands which are insulated with rubber. A cross-ply tyre designed for off-road use typically has two or three bundles. A radial on-road tyre normally only has one. The bead is considered the foundation of the tyre. It anchors the bead on the rim. The body ply of a radial tyre is The cord body is also known as made up of a single layer of steel the tyre carcass. It consists of cord wire. The wire runs from

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 159 layers of nylon plies. The cord bead to bead laterally to the body confines the pressure, which direction of motion (hence the supports the tyre load and term "radial plies"). The body ply absorbs shocks encountered is a primary component restricting during driving. Each cord in each the pressure which ultimately ply is completely surrounded by carries the load. The body ply also resilient rubber. These cords run transmits the forces (torque, diagonally to the direction of torsion, etc.) from the belts to the motion and transmit the forces bead and eventually to the rim. from the tread down to the bead. The belts are layers of steel cord wires located between the tread and the body ply. Off-road tyres can have up to five belts. Road The breakers are also known as tyres typically have one or two. belts. They provide protection for The steel wire of the belts run the cord body from cutting. They diagonally to the direction of also increase tread stability which motion. The belts increase the resists cutting. Breakers can be rigidity of the tread which made of nylon, aralon, or steel increases the cut resistance of the wire. tyre. They also transmit the torque forces to the radial ply and restrict tyre growth which prevents cutting, cut growth and cracking.

Comparison of radial vs. cross-ply performance This little table gives you some idea of the advantages and disadvantages of the two types of tyre construction. You can see the primary reasons why radial tyres are almost used on almost all the world's passenger vehicles now, including their resistance to tearing and cutting in the tread, as well as the better overall performance and fuel economy.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 160 Cross-ply Radial

Vehicle Steadiness

Cut Resistance - Tread

Cut Resistance - Sidewall

Reparability

Self Cleaning

Traction

Heat Resistance

Wear Resistance

Flotation

Fuel Economy

A subset of tyre construction: tyre tread Tread is much more than the shape of the rubber blocks around the outside of your tyre. The proper choice of tread design for a specific application can mean the difference between a comfortable, quiet ride, and a poor excuse for a tyre that leaves you feeling exhausted whenever you get out of your car.

A proper tread design improves traction, improves handling and increases durability. It also has a direct effect on ride comfort, noise level and fuel efficiency. Each part of the tread of your tyre has a different name, and a different function and effect on the overall tyre. Your tyres might not have all these features, but here's an example of what they look like, and what they're called.

Sipes are the small, slit-like grooves in the tread blocks that allow the blocks to flex. This added flexibility increases traction by creating an

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 161 additional biting edge. Sipes are especially helpful on ice, light snow and loose dirt.

Grooves create voids for better water channelling on wet road surfaces (like the Aqua-channel tyres below). Grooves are the most efficient way of channelling water from in front of the tyres to behind it. By designing grooves circumferentially, water has less distance to be channelled. Blocks are the segments that make up the majority of a tyre's tread. Their primary function is to provide traction.

Ribs are the straight-lined row of blocks that create a circumferential contact "band."

Dimples are the indentations in the tread, normally towards the outer edge of the tyre. They improve cooling.

Shoulders provide continuous contact with the road while manoeuvring. The shoulders wrap slightly over the inner and outer sidewall of a tyre.

The Void Ratio is the amount of open space in the tread. A low void ratio means a tyre has more rubber in contact with the road. A high void ratio increases the ability to drain water. Sports, dry-weather and high performance tyres have a low void ratio for grip and traction. Wet- weather and snow tyres have high void ratios.

Tread patterns There are hundreds if not thousands of car tyre tread patterns available. The actual pattern itself is a mix of functionality and aesthetics. In amongst all this, there are three basic types of tread

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 162 pattern that the manufacturers can choose to go with: Symmetrical: consistent across the tyre's face. Both halves of the tread-face are the same design.

Asymmetrical: the tread pattern changes across the face of the tyre.

These designs normally include larger tread blocks on the outer portion for increased stability during cornering. The smaller inner blocks and greater use of grooves help to disperse water and heat. Asymmetrical tyres tend to also be unidirectional tyres.

Unidirectional: designed to rotate in only one direction, these tyres enhance straight-line acceleration by reducing rolling resistance. They also provide shorter stopping distance. Symmetrical unidirectional tyres can be placed on either side of the vehicle, so the information on the sidewall will always include a rotational direction arrow. Asymmetrical unidirectional tyres must be dedicated to a specific side of the vehicle. The sidewall markings will indicate which side is 'out' and the correct direction of rotation.

Tread depth and tread wear indicators For the most part, motoring law in most countries determines that your tyres need a minimum tread depth to be legal. This varies from country to country but is normally around 1.6mm. To assist you in figuring out when you're getting close to that value, most tyres have tread wear indicators built into them.

If you look around the tread carefully, at some point you'll see a bar of rubber which goes across the tread and isn't part of the regular pattern (see the picture here for an example). This is the wear indicator. It's really basic, but it's also pretty foolproof. The tread wear indicator is normally moulded into the rubber at a depth of about 2mm.

As the rubber in your tyres wears away due to everyday use, the tread wears down. At some point, the tyre tread will become flush with the wear indicator (which is normally recessed into the tread). At this point you have about 2mm of tread left - in other words it is time to change tyres.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 163 Aquaplaning / hydroplaning One of the functions of your car's tyres is to pump water out of the tread on wet road surfaces. As the tyre spins, the tread blocks force water into the sipes and grooves and those channel water out and away from the contact patch where the tyre meets the road. As your tread wears down, the depth of the grooves and sipes gets less, which in turn reduces the tyre's ability to remove water.

At some point, the tread will get down to a point where even a light shower will turn any road into a dangerously slippery surface. This is called aquaplaning and how it happens is really simple: as you drive in the wet, your tyres form a natural but slight bow wave on the road surface. Some of the water escapes around the side of the tyre as spray whilst the rest goes under the tyre. The tyre tread pumps the water out to the sides and the contact patch remains in good contact with the road.

As the amount of water becomes more or deeper (heavier rain, or travelling faster for example), you end up with the tyre riding on a cushion of water as the volume of water in the 'bow wave' overcomes the tyre's ability to disperse it. At this point, it doesn't matter what you do - braking, accelerating and steering have no effect because the tyre is actually making no contact with the road surface any more.

The worst thing you can do is to brake, because stopping the rotation of the wheels removes any last chance the tyres have at removing the water. If you let off the accelerator instead, as wind resistance and other factors begin to slow you down, at some point you'll go back through the critical depth of water and the tyres will begin to grip again.

Under good conditions, with As conditions worsen - less adequate tread, light water At this point, the tread is drainage, higher speed or build-up and good road overwhelmed with water and more rain, the amount of drainage, the tyre tread is is no longer effective. Water is water on the road surface able to disperse the water incompressible so the tyre is increases. The tread is only from the road surface so that lifted off the road and skates able to disperse so much the tyre's contact patch across the surface of the water, and begins to become remains in good contact with water. submersed. the road.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 164 Coloured dots and stripes - what’s that all about? When you're looking for new tyres, you'll often see some coloured dots on the tyre sidewall, and bands of colour in the tread. The dots on the sidewall typically denote unformity and weight. It's impossible to manufacture a tyre which is perfectly balanced and perfectly manufactured in the belts. As a result, all tyres have a point on the tread which is lighter than the rest of the tyre - a thin spot if you like. It's fractional - you'd never notice it unless you used tyre manufacturing equipment to find it, but its there.

When the tyre is manufactured, this point is found and a coloured dot is put on the sidewall of the tyre corresponding to the light spot. Typically this is a yellow dot and is known as the weight mark. Typically the yellow dot should end up aligned to the valve stem on your wheel and tyre combo. This is because you can help minimize the amount of weight needed to balance the tyre and wheel combo by mounting the tyre so that its light point is matched up with the wheel's heavy balance point.

What about the coloured stripes in the tread? Often when you buy tyres, there will be a coloured band or stripe running around the tyre inside the tread. These can be any colour and can be placed laterally almost anywhere across the tread. The lines are sprayed on to the rubber tread stock after it has been extruded during the manufacturing process. Think of them like a barcode. They can sometimes indicate the rubber compound or the intended tyre size and often you'll find other information printed on to the tread as well as the stripes.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 165 Caster, camber, toe-in toe-out alignment This is the general term used to cover the next three points:

Caster This is the forward (negative) or backwards (positive) tilt of the spindle steering axis. It is what causes your steering to 'self-centre'.

Correct caster is almost always positive. Look at a bicycle - the front forks have a quite obvious rearward tilt to the handlebars, and so are giving positive caster.

The whole point of it is to give the car (or bike) a noticeable centre point of the steering - a point where it's obvious the car will be going in straight line.

Camber Camber is the tilt of the top of a wheel inwards or outwards (negative or positive). Proper camber (along with toe and caster) makes sure that the tyre tread surface is as flat as possible on the road surface. If your camber is out, you'll get tyre wear.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 166 Too much negative camber (wheels tilt inwards) causes tread and tyre wear on the inside edge of the tyre. Similarly, too much positive camber causes wear on the outside edge.

Negative camber is what counteracts the tendency of the inside wheel during a turn to lean out from the centre of the vehicle. 0 or Negative camber is almost always desired. Positive camber would create handling problems.

The technical reason for this is because when the tyres on the inside of the turn have negative camber, they will tend to go toward 0 camber, using the contact patch more efficiently during the turn.

If the tyres had positive camber, during a turn, the inside wheels would tend to even more positive camber, compromising the efficiency of the contact patch because the tyre would effectively only be riding on its outer edge.

Toe in and out 'Toe' is the term given to the left-right alignment of the front wheels relative to each other. Toe-in is where the front edge of the wheels are closer together than the rear, and toe-out is the opposite.

Toe-in counteracts the tendency for the wheels to toe-out under power, like hard acceleration or at motorway speeds (where toe-in disappears).

Toe-out counteracts the tendency for the front wheels to toe-in when turning at motorway speeds. A typical symptom of too much toe-in is excessive wear and feathering on the outer edges of the tyre tread section.

Similarly, too much toe-out will cause the same feathering wear patterns on the inner edges of the tread pattern.

Rotating your tyres This is the practice of swapping the front and back tyres to even out the wear. It results in even overall tyre wear.

The frequency of rotation of your tyres depends on whether you have 2- , 4-, front- or rear-wheel drive, and whether or not you have unidirectional tyres (those with tread designed only to spin in one

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 167 direction). With unidirectional tyres, you can swap the front and rear per-side, but not swap them side-to-side. If you do, they'll all end up spinning the wrong way for the tread.

Generally speaking you ought to rotate your tyres every 5,000 miles (8,000km) or so, even if they're showing no signs of wear. The following table shows the correct way to rotate your tyres.

front wheel drive rear wheel drive 4 wheel drive any unidirectional tyre non unidirectional non unidirectional non unidirectional

Diagnosing problems from tyre wear Your tyre wear pattern can tell you a lot about any problems you might be having with the wheel/tyre/suspension geometry setup.

The first two signs to look for are over- and under-inflation. Whilst this used to be a problem on older tyres, modern radials have much stiffer carcasses but even so, you might still be able to spot the following:

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 168 Trouble Shooting Chart for Tyre Wear

Here's a generic fault-finding table for most types of tyre wear if you can spot them:

Problem Cause Shoulder Wear  Under-inflation Both shoulders wearing faster  Repeated high-speed cornering  Improper matching of rims and tyres than the centre of the tread  Tyres haven't been rotated recently Centre Wear* The centre of the tread is  Over-inflation  Improper matching of rims and tyres wearing faster than the  Tyres haven't been rotated recently shoulders One-sided wear  Improper wheel alignment (especially One side of the tyre wearing camber) unusually fast  Tyres haven't been rotated recently  Faulty suspension, rotating parts or brake parts Spot wear  Dynamic imbalance of tyre/rim A part (or a few parts) of the assembly circumference of the tread are  Excessive runout of tyre and rim wearing faster than other parts. assembly  Sudden braking and rapid starting  Under inflation  Faulty suspension, rotating parts or Diagonal wear brake parts A part (or a few parts) of the  Improper wheel alignment  Dynamic imbalance of tyre/rim tread are wearing diagonally assembly faster than other parts.  Tyres haven't been rotated recently  Under inflation Feather-edged wear The blocks or ribs of the tread  Improper wheel alignment (faulty toe- in) are wearing in a feather-edge  Bent axle beam pattern

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 169 GLOSSARY AUTOMOTIVE TERMS Back to ToC ABS Acronym for "Anti-lock Brake System." Vehicles equipped with ABS use wheel speed sensors and a computer-controlled brake pressure regulator to prevent wheel lock-up during sudden stops. When the computer senses one wheel is slowing faster than the others (indicating it is about to lock-up and skid), the computer reduces brake pressure to that wheel by momentarily isolating brake pressure, releasing pressure then reapplying pressure in rapid sequence. ACKERMAN PRINCIPLE The creation of toe-out when turning to minimize wear. To create the proper geometry, the steering arms are angled to turn the inside wheel at a sharper angle than the outside wheel. This allows the inside wheel to follow a smaller radius circle than the outside wheel. AIR CONDITIONING (A/C) A system that cools and dehumidifies air entering the passenger compartment. The system uses a refrigerant to cool the air and carry heat away from the passenger compartment. Major system components include a compressor, condenser, evaporator, accumulator or receiver/dryer, and orifice tube or expansion valve. AIR FILTER A filter used to keep dirty air from entering the engine. The filter element is typically resin impregnated cellulose fibers (paper) with a mixture of synthetic fibers. The filter is located in a housing that is attached to the throttle body, or in a housing that sits atop the . AIRFLOW SENSOR A device that is used in many electronic fuel injection systems for measuring the volume of air entering the engine. Some use a spring loaded vane while others use a hot wire or heated filament to sense air flow. AIR/FUEL RATIO This is the relative proportion of air and fuel delivered by the carburetor or fuel injection to the engine. The "ideal" air/fuel ratio is 14.7 parts of air to every one part fuel. Less air or more fuel and the mixture is said to be rich. More air or less fuel and the mixture is said to be lean. Rich mixtures provide more power but also use more fuel and increase exhaust emissions. Lean mixtures use less fuel, but if too lean cause misfiring at idle.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 170 AIR TEMPERATURE SENSOR This sensor measures the temperature of air in the intake stream or intake manifold. An air temperature value is needed by the PCM to calculate the air/fuel ratio, as air density changes with temperature. ALIGNMENT Although most people think of the front wheels when alignment is mentioned, it actually refers to all four wheels. All four wheels should be perpendicular to the road and parallel to one another for the best handling, traction and tire life. If the wheels are out of alignment, rapid or uneven tire wear, and/or a steering pull to one side can result. ALL-WHEEL DRIVE (AWD) A vehicle (usually a car) where all four wheels are driven. Most are fulltime systems for year-round driving, and use a viscous fluid coupling center differential instead of a transfer case to route drive torque to all four wheels. This allows the front and rear wheels to turn at slightly different speeds when turning on dry pavement. ALTERNATOR The component in a vehicle's charging system that makes electricity. The alternator's job is to keep the battery fully charged, and to provide additional current to meet the demands of the ignition system, lights and other accessories. Alternator capacities are rated in amps, with typical outputs ranging from 50 to 80 amps. AUTOMATIC TRANSMISSION A type of transmission that shifts itself. A fluid coupling or torque converter is used instead of a manually operated clutch to connect the transmission to the engine. Newer automatics use electronic controls to regulate shifting and torque converter lockup. AXLE, FRONT A crossbeam that supports the weight of the vehicle (typically a truck) and is connected to the spindles with king pins. AXLE, REAR May refer to the drive axles that connect both rear wheels to a center differential in a rear-wheel drive vehicle, or a crossbeam that connects both rear wheels and supports the rear of the vehicle in a front-wheel drive application.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 171 BALL JOINT A flexible coupling in a vehicle's suspension that connects the control arm to the steering knuckle. A ball joint is so named because of its ball- and-socket construction. Some are designed to never require grease while others should be lubed every six months. As the joint wears, it becomes loose. The result is suspension noise and wheel misalignment. BAROMETRIC PRESSURE SENSOR A device that senses barometric pressure for the engine control system. May be combined with a Manifold Absolute Pressure (MAP) sensor. BATTERY The battery is a storehouse of electrical energy for starting the engine. All cars and light trucks today have a 12-volt battery. Most are also maintenance-free, meaning you do not have to add water to them periodically. Batteries are rated according to their Cold Cranking Amp (CCA) capacity. The higher the CCA rating of the battery, the better. A typical passenger car battery might be rated at 500 CCA or higher. BOOTS Also called bellows, these are the protective rubber (synthetic or natural) or hard plastic (usually Hytrel) covers that surround CV joints. The boot's job is to keep grease in and dirt and water out. Split, torn or otherwise damaged boots should be replaced immediately. Old boots should never be reused when servicing a joint. Always install new boots. This is the process of removing air bubbles from the brake system by pumping fluid through the lines. Air bubbles are bad because they compress when pressure is applied resulting in a low or spongy feeling pedal. BRAKE CALIPERS The part of the disc brake that squeezes a pair of brake pads against the rotor. A caliper is nothing more than a casting with a piston inside. When hydraulic pressure pushes the piston out, it forces the brake pads against both sides of the rotor. Some calipers are "floating" in that they slide back and forth and self-center over the rotor. BRAKE DRUMS The cast iron housing and friction surface around a drum brake. The brake shoes expand outward and rub against the inside surface of the drums when the brakes are applied. Worn drums often take on a grooved appearance. The inner surface should be turned smooth on a brake lathe when the shoes are replaced.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 172 BRAKE FLUID The brake system uses a glycol-based hydraulic fluid. The fluid is "hygroscopic," which means it tends to absorb moisture over time. Moisture lowers the boiling point of the fluid and causes internal corrosion in the brake system. That is why the fluid should be replaced when brake repairs are made or every two years for preventive maintenance. BRAKE PADS These are the linings used in the front disc brakes. They are called pads because of their flat pad-like shape. Each brake uses a pair of pads (one inner, one outer). Replacement pads are sold in two-pair sets, and are fairly easy to change. Calipers should be inspected for leaks, and the rotors resurfaced to restore a smooth surface. BRAKE ROTORS The flat disk-like plates that provide the friction surface in a disc brake. When hydraulic pressure is applied to the caliper, the brake pads are squeezed against both sides of the rotor producing friction and heat. Some rotors have cooling fins between both faces and are called "vented" rotors. BRAKES The brake system uses hydraulic pressure to stop the vehicle when you step on the brake pedal. Pushing the pedal down pumps fluid from the master cylinder to the brakes at each wheel. This squeezes the brake linings against the rotors and drums, creating friction which brings the vehicle to a halt. BRAKE SHOES The brake linings used in drum brakes (the rear brakes on most cars). Each drum contains two shoes (a primary or leading shoe, and a secondary or trailing shoe). CAMBER A wheel alignment angle that refers to the inward or outward tilt of the wheels as viewed from the front. Outward tilt is called "positive" camber while inward tilt is called "negative." Ideally, the wheels should have zero rolling camber (perpendicular to the road) when the vehicle is loaded. Camber changes as the vehicle is loaded and the suspension sags.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 173 CAMSHAFT A shaft inside an engine that has lobes to operate the engine's valves. In "pushrod" engines, lifters ride on the cam lobes. The up and down motion is transferred through push rods and rocker arms to actuate the valves. In an "overhead" cam engine, the cam may push directly on the tops of the valves or work the valves through short rocker arms. CARBON DIOXIDE (CO2) A harmless, odorless gas composed of carbon and oxygen. It is the byproduct of complete combustion. But it is also a greenhouse gas that contributes to global warming. CARBON MONOXIDE (CO) A deadly gas that results from the incomplete burning of gasoline inside the engine, carbon monoxide is considered to be a serious air pollutant. You can't see it or smell it, but it can kill in very small concentrations. Because of this you should never run an engine inside a closed garage. CARBURETOR A component used to deliver air and fuel on older engines. It mixes air and fuel in varying proportions according to the position of the throttle opening and engine vacuum. Carburetor adjustments include idle speed, idle fuel mixture and choke setting. Most carburetor problems are due to choke misadjustment or dirty air or fuel. CARDAN JOINT Also known as a Hooke Joint, Universal Joint or U-Joint, it is a simple flexible coupling using a double yoke and four-point center cross. Cardan joints are used as couplings in the driveshafts of rear-wheel drive cars. Because they can produce uneven shaft speeds when operated at joint angles of more than a few degrees, they are usually not used with front-wheel drive (because the front wheels also steer and create large operating angles). CASTER A wheel alignment angle that refers to the forward or rearward tilt of the steering axis on the front wheels. A forward tilt of the steering axis is called "negative" caster while a rearward tilt is called "positive." The caster angle has no affect on tread wear but it does affect steering return and stability. Most vehicle have a certain amount of positive caster. The higher the caster angle the more steady the car feels at high speed.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 174 CATALYTIC CONVERTER The converter is an emissions control device in the exhaust system that reduces the amount of pollutants that come out the tailpipe. It does this by reburning certain pollutants and reforming others. Platinum, palladium and rhodium catalysts act as triggers for the chemical reactions. CENTRIFUGAL ADVANCE A mechanical means of advancing spark timing with flyweights and springs to compensate for changing engine speed (rpm). The weights are located inside the distributor on older vehicles with electronic ignition systems. The size of the weights, the amount of spring tension, and engine rpm determine the rate and amount of advance. Advancing the spark timing as engine speed increases is necessary for good fuel economy and performance. CHASSIS The frame or undercarriage of a vehicle. On unibody vehicles, the lower structure to which the suspension is attached. CHARGING SYSTEM The charging system includes the alternator, voltage regulator which is often a part of the alternator itself), the battery, and the indicator gauge or warning light on the dash. The charging system's job is to generate enough current to keep the battery fully charged, and to satisfy the demands of the ignition and electrical systems. The voltage regulator senses the demands on the electrical system, and controls alternator output so sufficient current is produced. CHECK VALVE A valve which permits the passage of a gas or fluid in one direction, but not in the other. For example, the check valve between the air pump and exhaust manifold in an air injection system allows air to flow to the manifold, but stops exhaust gas from entering the air pump in the event that the pump belt breaks. A check valve in the master brake cylinder allows brake fluid to flow in one direction only. CLOSED LOOP The basic principle of electronic engine management in which input from an allows the engine control computer to determine and maintain a nearly perfect air-fuel ratio. To enter closed loop operation, the oxygen sensor must be producing a voltage signal and the engine must have reached a certain operating temperature.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 175 CLUTCH A device that couples the engine to the transmission. The clutch consists of a friction-lined disk (called the "clutch disk") and a spring- loaded "pressure plate" that presses the clutch disk tightly against the flywheel. When you push in on the clutch pedal, the linkage releases the spring pressure allowing the clutch disk to slip. COIL SPRINGS A type of spring made of wound heavy-gauge steel wire used to support the weight of the vehicle. The spring may be located between the control arm and chassis, the axle and chassis, or around a MacPherson strut. Coil springs may be conical or spiral wound, constant rate or variable rate, and wound with variable pitch spacing or variable thickness wire. COMPRESSION The amount by which the air volume in a cylinder is reduced or compressed by the upward stroke of the piston. See Compression Ratio. Compression can be measured mechanically by installing a compression gauge in a spark plug hole, disabling the ignition and cranking the engine, or electronically by an engine analyzer during a cranking test. COMPRESSION RATIO The relationship between the piston cylinder volume from bottom dead center to top dead center. Higher compression ratios improve combustion efficiency but also require higher-octane fuels. Pre- emission control engines often had compression ratios as high as 11.5:1 whereas most of today's engines are between 8.5:1 and 9.5:1. Diesel engines have very high compression ratios, from 18:1 to 22:1. COMPUTERIZED ENGINE CONTROLS A microprocessor based engine management systems that utilizes various sensor inputs to regulate spark timing, fuel mixture, emissions and other functions. Used on most vehicles since 1981 to comply with federal emission regulations. Diagnosis usually requires accessing trouble codes and/or putting the system into a special diagnostic mode. CONSTANT VELOCITY (CV) JOINT A Constant Velocity Joint is one that provides consistent driveshaft speeds regardless of the operating angle of the joint. CV joints are used primarily in on the driveshafts of front-wheel drive vehicles, and they come in two basic varieties: the Rzeppa ball type joints (which you will find on the outer end of the driveshaft) and tripod joints (which are used on the inner end).

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 176 COOLANT The liquid inside the radiator and cooling system is called the "coolant" because it cools the engine. It circulates through the engine and soaks up heat. The coolant then flows to the radiator where it sheds its heat. When the heater is turned on, coolant also flows through the heater core (which acts like a miniature radiator) to heat air entering the passenger compartment. COOLANT TEMPERATURE SENSOR A variable resistance thermistor which changes resistance as the engine's coolant temperature changes. The sensor's output is monitored by the engine computer to regulate various ignition, fuel and emission control functions, and to turn the radiator cooling fan on and off as needed. In the PTC (Positive Temperature Coefficient) type of sensor, ohms go up with temperature. In the more common NTC (Negative Temperature Coefficient) type, resistance goes down as heat goes up. COOLING SYSTEM The cooling system consists of the radiator, water pump, thermostat, heater core, heater and radiator hoses, and the water jackets inside the cylinder head and engine block (See Coolant, Radiator and Water pump). An engine produces a tremendous amount of waste heat when it runs, so some means of cooling is needed to prevent the engine from self-destructing. CRANKSHAFT The main shaft inside the engine that turns the up-and-down motion of the pistons into rotational torque. There are two types of : cast iron and forged steel. The cast variety are used in most passenger car engines while the stronger forged ones are used primarily in high performance applications. CRANKSHAFT POSITION (CKP) SENSOR A type of sensor used to monitor the position of the crankshaft. The sensor's input is used to trigger the ignition system. There are two basic types: magnetic and hall effect. The sensor reads notches in a ring mounted on the crankshaft, harmonic balancer or flywheel. DIAGNOSTIC TROUBLE CODE (DTC) Computerized engine control systems have a certain amount of built-in self-diagnostic capability to detect problems that affect engine performance and emissions. The same is true for the antilock brake system and other onboard systems that are computer controlled. When a fault is detected, the computer will store a diagnostic trouble code in its memory and illuminate the "Check Engine" light.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 177 DIESEL ENGINE A type of engine that uses compression to ignite its fuel rather than a spark. A diesel engine has a much higher compression ratio than a gasoline engine (22:1 versus 8:1 for example), and because of this it is able to squeeze more usable power out of each drop of fuel. A typical diesel gets 30 to 50 percent better fuel mileage than a comparable gasoline engine of equal displacement. A diesel engine has no carburetor or throttle. Fuel is injected directly into the engine’s cylinders through high pressure injectors. Injector timing is very important because it affects idle quality, rattling and exhaust smoke. Engine speed is governed by the injection pump which controls the amount of fuel delivered. Newer diesels use electronic injectors and computer controls to reduce emissions. Most passenger car diesel engines have a glow plug starting system that preheats the combustion chamber. DIFFERENTIAL This is the gear box between the drive axles that transfers torque from the driveshaft to the axles and allows the drive axles to rotate at different speeds. This is necessary because the inner wheel follows a smaller arc than the outer one when the vehicle turns. The differential always provides power to the wheel that needs it least, because the gears always allow torque to follow the path of least resistance. DIODE An electrical component used to control the flow of electricity in one direction. Used in alternators to convert alternating current into direct current. Diodes are part of the alternator’s rectifier assembly. DISC BRAKES A type of brake design that uses a flat disk-shaped rotor as the friction surface. A caliper squeezes a pair of brake pads against the rotor to stop the vehicle. Disc brakes are used on the front wheels of most passenger cars, and sometimes on the rear. DISTRIBUTOR The "brain" of the ignition system that "distributes" ignition voltage to each of the spark plugs. The distributor contains an electronic trigger or pickup device (older cars use contact points) that trigger the . High voltage enters the distributor cap from the coil, travels down through the rotor to the appropriate spark plug terminal and exits out the wire. On pre-computer cars, the distributor also controls spark timing via centrifugal and vacuum advance units, but this function is performed by the computer in late model cars.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 178 DISTRIBUTORLESS IGNITION SYSTEM (DIS) An ignition system that does not use a distributor to route high voltage to the spark plugs. The high voltage plug wire runs directly from the ignition coil to the spark plug. Some DIS systems have one coil for every two spark plugs (a shared system), while others have a separate coil for each spark plug. Eliminating the distributor makes the system more reliable and eliminates maintenance. DRIVESHAFT The propeller shaft that transmits engine torque to the differential, or from the differential to the drive wheels. In front-wheel drive vehicles, the two driveshafts are often referred to as "halfshafts." ELECTRICAL SYSTEM The battery, wires and electrically-operated accessories in a vehicle. All modern passenger cars, light trucks and most large have 12-volt electrical systems. Most heavy-duty trucks use 24-volt systems. The electrical system uses the battery and charging system as its power source, with wires and switches routing the voltage to where it is needed. The metal body serves as the ground or return path for the voltage back to the battery. The electrical system is protected against damage by various devices. ELECTRONIC FUEL INJECTION (EFI) Abbreviation for Electronic Fuel Injection. This type of system uses computer-controlled fuel injectors to spray fuel into the engine rather than mechanically controlled injectors or a carburetor. EFI comes in several varieties: "throttle body injection", "multi-port injection" or Sequential Fuel Injection (SFI). Electronic fuel injection is considered to be superior to carburetion because it allows more precise fuel metering for easier starting, lower emissions, better fuel economy and performance. EMISSION CONTROL SYSTEM The vehicle components that are responsible for reducing air pollution. This includes crankcase emissions, evaporative emissions and tailpipe exhaust emissions. Crankcase emissions consist of unburned fuel and combustion byproducts. These gases are re-circulated back into the engine for re-burning by the Positive Crankcase Ventilation (PCV) system.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 179 EXHAUST SYSTEM The exhaust system consists of the exhaust manifold, exhaust pipe, catalytic converter, and tailpipe. The system performs three important jobs: it carries exhaust gases away from the engine, it quiets the engine, and it helps control pollution. The exhaust systems one weakness is its vulnerability to corrosion. FAST IDLE The higher speed at which an engine idles during warm-up. When first started, a cold engine needs more throttle opening to idle properly. On carbureted engines without computer idle speed control, a set of cam lobes on the choke linkage provides a fast idle speed (850 to 1200 rpm) during engine warm-up. The order in which the spark plugs fire. The firing order will vary depending on the engine application. The firing order must be correct otherwise the engine may not start or run properly. FLYWHEEL A large heavy wheel on the end of the crankshaft that helps the engine maintain momentum when the clutch is engaged. The flywheel also helps dampen engine vibrations. The flywheel should be resurfaced when the clutch is replaced to restore a smooth surface. Oil or grease on the surface of the flywheel can make the clutch slip and chatter. FOUR-WHEEL DRIVE (4WD) A method of driving a vehicle by applying engine torque to all four wheels. Various schemes are used for 4WD including part-time, full- time and variable four-wheel drive. The primary advantage of four- wheel drive is increased traction, which is especially useful for off-road excursions or severe weather driving, but is of little practical value for normal driving. Because of the added friction in the drivetrain, a four- wheel drive vehicle typically gets significantly lower fuel mileage than a front- or rear-wheel drive vehicle. FRONT-WHEEL DRIVE (FWD) A means of driving a vehicle by applying engine power to the front wheels instead of the rear wheels. There are advantages and disadvantages to front-wheel drive. On the plus side, the advantages go mostly to the vehicle manufacturers because it makes it easier for them to package a vehicle engine/drivetrain/body combination more efficiently. In other words, the same basic engine/drivetrain package can be installed under a variety of "different" model cars.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 180 FUEL FILTER A device installed in the fuel line to trap contaminants before they reach the engine. A plugged fuel filter can cause the engine to stall. The fuel filter should be replaced periodically for preventive maintenance. FUEL INJECTION A method of fuel delivery whereby fuel is sprayed into the intake manifold or intake ports through a nozzle. FUEL PUMP A pump that moves fuel from the fuel tank to the engine. On older vehicles with , a low pressure engine-mounted mechanical fuel pump is used. On newer vehicles with electronic fuel injection, a high pressure electric fuel pump is used. If the fuel pump fails, the engine will stop and not restart. FUSE A fuse is a protective link in a wiring circuit that is designed to burn out in case of an overload. The fuse has a tiny wire inside it that is designed to melt if the current exceeds a certain value. When the wire melts, it breaks the circuit and protects against damage or fire. Most fuses are located in the fuse box under the dash, although "in-line" fuses may be hidden elsewhere. GASKET A means of sealing the mating surfaces between various components. Gaskets are used between the various parts of the engine to keep oil, coolant, air and fuel in their respective places. Rubber, cork or combination cork/rubber gaskets are often used to seal the oil pan, valve covers, waterpump and timing chain cover. Metal gaskets are used between the cylinder head and engine block, and metal or asbestos gaskets are used to seal intake and exhaust manifolds. HALFSHAFT The name given to either of the two driveshafts that run from the transaxle to the wheels in a front-wheel drive vehicle. Halfshafts may be of solid or tubular construction, and of equal or unequal length side-to- side. IDLE ADJUSTMENT Adjusting the engine idle speed. Idle is not adjustable on many late model engines with computerized idle speed controls. IDLE MIXTURE The air/fuel ratio that is delivered through the carburetor when the engine is idling. It can be adjusted by turning the idle mixture adjustment screw(s) on the carburetor. The screw opens up a little passage that lets more or less fuel into the engine. On most late model

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 181 vehicles, the idle mixture screws have caps that allow only limited adjustment, or they are sealed to prevent tampering. The relative richness or leanness of the idle mixture has a big effect on tailpipe emissions at idle. IDLE SPEED This refers to how fast the engine runs when idling. It can usually be adjusted by turning a screw on the carburetor throttle linkage, or by turning an air bypass screw on a fuel injection throttle body. On most newer cars, however, it is computer-controlled and non-adjustable. The idle speed is programmed into the computer, and the computer regulates idle speed by opening and closing the idle air control valve. IGNITION COIL The component in the ignition system that turns low voltage into high voltage to fire the spark plugs. When 12-volts passes through the coil's primary windings, it creates a strong magnetic field. Then when the current is shut off (by the ignition module or the opening of the contact points in older ignition systems), the magnetic field causes a surge of high voltage (as much as 40,000 volts) in the coil's secondary windings. IGNITION MODULE The electronic control for the ignition system. The module receives a signal from a magnetic pickup or Hall effect sensor in the distributor. The module uses this signal to open and close the ground circuit to the ignition coil to fire the spark plugs. The ignition module itself may be located inside the distributor, on the distributor housing or in the engine compartment. IGNITION SYSTEM The various components that control the igniting of fuel in the engine's cylinders. The ignition system has two parts: the primary side (the distributor and electronic control module), and the secondary side (the ignition coil, distributor cap, rotor, spark plug wires and spark plugs). INLINE FILTER A filter which may be installed in a fuel line, power steering pump discharge line, or A/C compressor discharge line to trap debris that might cause damage.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 182 INJECTOR The component in a diesel or gasoline fuel injection system that squirts fuel into the engine. In gasoline engine applications, the injector is usually electrically triggered. Varnish and dirt can build up in the nozzle opening restricting the flow of fuel. Injectors can be cleaned by using various fuel additives. In most diesel engines, the injectors are mechanical and deliver fuel under very high pressure directly into the cylinders. A heat exchanger that is added to a turbocharged engine to cool the air after it leaves the turbo. This increases air density and means more air can be pumped into the engine. The result is roughly a 10 to 15 percent improvement in horsepower. JUMP STARTING A technique of starting one vehicle using another vehicle's battery. A pair of jumper cables are required to connect the terminals of both batteries together (positive to positive, negative to negative). KINGPIN A pin that serves as the pivot or hinge for the steering knuckle, used primarily on trucks with I-beam axles and older vehicles that do not have ball joints. LEAF SPRINGS A type of spring made out of a flat strip or individual leaves. Most are steel, but some are made of lightweight composite materials. MACPHERSON STRUT A special kind of oversized shock absorber that is used as part of the vehicle's suspension. When used on the front suspension, it replaces the upper control arm and ball joint. Some struts have coil springs around them while others do not. Some struts have replaceable internal components that can be repaired by dropping in a new cartridge. MALFUNCTION INDICATOR LAMP (MIL) The "Check Engine" on the instrument panel light that comes on when the onboard diagnostic system detects a fault. The MIL light will come on to alert the driver if a fault may cause vehicle emissions to exceed federal emission limits. A vehicle with an illuminated MIL lamp will NOT pass an OBD II plug-in emissions test. MANIFOLD VACUUM The amount of vacuum created in the intake manifold by the pumping action of the engine's pistons. Vacuum is highest at idle and lowest at wide open throttle. Vacuum is measured in inches or millimeters of mercury.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 183 MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR Refers to a manifold absolute pressure sensor, a variable resistor used to monitor the difference in pressure between the intake manifold at outside atmosphere. This information is used by the engine computer to monitor engine load (vacuum drops when the engine is under load or at wide open throttle). MASS AIRFLOW SENSOR (MAF) A device used in many fuel injected engines to measure the amount of air entering the engine so the computer can control the air/fuel mixture. Located ahead of the throttle body, the MAP sensor uses a heated wire or filament to measure airflow. MASTER CYLINDER When you step on the brake pedal, it pushes a piston inside the master cylinder which produces hydraulic pressure inside the brake system. The brake fluid reservoir is located on top of the master cylinder, and you will find both mounted on the firewall in the engine compartment on the driver's side of the vehicle. MFI Abbreviation for Multi-port Fuel Injection, a type of fuel injection system that has one injector for each engine cylinder. Each injector sprays its fuel directly into the intake port in the cylinder head. MUFFLER The device in the exhaust system that quiets the exhaust. A muffler is nothing more than a steel can full of baffles. NEUTRAL STEERING A vehicle that neither understeers or oversteers. It responds predictably and evenly to steering inputs when cornering. OBD II Onboard Diagnostics II, A second generation emissions diagnostic system required on all 1996 and newer vehicles (though some 1994 and 1995 model year vehicles were equipped with early versions of the system). The OBD II system monitors vehicle emissions, and illuminates the Check Engine or Malfunction Indicator Lamp (MIL). OCTANE This is a measure of a fuel’s resistance to detonation. The higher the number, the better the fuel. Typical unleaded regular octane ratings range from 86 to 88. Premium grade unleaded fuels start around 89 and go as high as 93 or 94.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 184 OIL CONSUMPTION All engines use a small amount of oil over time. It gets past the piston rings and valve guide seals and is burned in the combustion chamber. A small amount escapes through the PCV system and a few drops usually managed to seep through a gasket or seal. OIL COOLER A heat exchanger for cooling oil. Most automatic transmissions are equipped with an oil cooler that’s located inside the radiator. OIL PRESSURE The amount of pressure created in an engine’s oil system by the oil pump. A certain amount of oil pressure is needed to circulate oil throughout the engine and to maintain adequate lubrication. Low oil pressure or loss of pressure is dangerous because it can lead to expensive engine damage. Oil pressure is monitored by a sending unit mounted on the engine block. ONBOARD DIAGNOSTICS (OBD) Software in the engine control module or powertrain control module that runs self-diagnostic checks on the control module, sensors and other related systems. When a fault is found, the software sets a diagnostic trouble code and turns on the MIL lamp. OVERHEAD CAM (OHC) This refers to a type of engine design that positions the camshaft in the cylinder head over the valves. It is a popular design on many four- cylinder, V6 and even some V8 engines. On engines that use a rubber belt to drive the overhead cam, the belt usually needs to be replaced somewhere around 60,000 to 90,000 miles (see the owner’s manual for specific recommendations). OVERSTEER A handling trait wherein a vehicle tends to overrespond to changes that are made in the direction of the steering wheel. The rear end on a vehicle that oversteers will tend to spin around when the vehicle is turned sharply. OXYGEN SENSOR A component in the engine's computer control system that monitors the amount of oxygen in the exhaust. The computer uses this information to change the relative richness or leanness of the air/fuel mixture. Located in the exhaust manifold, the O2 sensor resembles a small spark plug on the outside. But inside it has a special zirconium element that produces a varying voltage once it gets hot.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 185 A mechanical brake for locking the rear wheels when parking. When you pull on the parking brake handle or step on the parking brake pedal, it pulls a pair of cables that extend to the rear brakes. The cables work a lever mechanism that binds the rear shoes against the drums, or on rear disc brake-equipped vehicles locks the pads (or a pair of mini- shoes) against the rotor. PCV VALVE The Positive Crankcase Ventilation valve is an emissions control device that routes unburned crankcase blowby gases back into the intake manifold where they can be reburned. The PCV system is one of the oldest emission control devices, and also one of the most beneficial. PITMAN ARM The arm connected to the steering box sector shaft that moves side to side to steer the wheels. POSITIVE CRANKCASE VENTILATION A means of controlling crankcase blowby emissions and removing moisture condensation from the crankcase to prolong oil life. POWER BRAKES Most vehicles use a vacuum booster to increase the pedal force applied to the master cylinder. Some use a hydraulic power unit that does the same thing with hydraulic pressure rather than vacuum. Power brakes require no special maintenance, but if the booster goes bad pedal effort will be noticeably higher. POWER STEERING A means of hydraulically assisted steering. A belt-driven power steering pump creates system pressure. The pressurized fluid is then routed into a cylinder that helps push the wheels one way or the other when the steering wheel is turned. The two most common power steering complaints are noise and leaks. A slipping drive-belt on the power steering pump can produce a loud squeal, especially when turning sharply. RACK & PINION STEERING A type of lightweight steering gear that uses a worm-like gear (the pinion) to drive a horizontal bar (the rack). The primary advantage of rack & pinion steering is that it is lightweight and uses fewer parts than a reciprocating ball steering gear.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 186 RADIAL TIRE A type of tire that is constructed with the reinforcing belts sideways under the tread rather than lengthwise. This makes the tire more flexible which reduces rolling resistance to improve fuel economy (See Tire Ratings). A radial tire can be identified by looking for the letter "R" in the size designation on the tire's sidewall. RADIATOR The part of the cooling system that gets rid of the engine heat. Coolant from the engine flows past the thermostat and into the radiator where it is cooled by air passing through the fins. Internal corrosion and hairline cracks caused by vibration are the two primary causes of radiator leaks. REAR-WHEEL DRIVE (RWD) A method of driving a vehicle whereby engine power is applied to the rear wheels. Power from the engine flows through the transmission, down the driveshaft, through the differential to the rear axles and wheels. RECIRCULATING BALL STEERING A type of steering gear normally used with a parallelogram steering linkage. So named because of the ball bearings that are recirculated in the gear box between the worm and sector gears to reduce friction. REFRIGERANT The working agent in an A/C system that absorbs, carries and releases heat. The two primary automotive refrigerants are R12 and R134a, but many other substances have similar properties (primarily a low boiling temperature) that allow them to be used as "alternative" refrigerants. RELAY An electrical device that uses an electromagnetic switch and contact points to turn on and off various high amperage electrical accessories. Most vehicles have a horn relay, a headlight relay, a relay for the rear window defogger, and relays for various other things such as the blower motor. RPM Abbreviation for Revolutions Per Minute. Engine speed is often expressed as so many rpm. SCAN TOOL A diagnostic tool that is plugged into a vehicle's diagnostic connector to read fault codes, sensor data and other system information. The software in the tool must be compatible with the vehicle application, and may only be able to access or display limited information.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 187 SEQUENTIAL MULTIPORT FUEL INJECTION (SFI) A type of fuel injection system that uses a separate fuel injector for each cylinder, and pulses the injectors individually. SERPENTINE BELT A type of flat rubber drive belt that is used to turn multiple accessories on the front of an engine. It is called a serpentine belt because of the way it snakes around the various pulleys. Many vehicles now have a single serpentine drive belt because it eliminates the need for several separate V-belts. A spring-loaded pulley maintains tension on the serpentine belt. SHACKLE A link that connects a leaf spring to the chassis or frame. The shackle allows the length of the spring to change as the suspension moves up and down. SHOCK ABSORBER A part of the suspension that is designed to dampen up-and-down wheel motions that result from bumps and chassis movement. Each wheel has its own shock absorber, which is nothing more than a fluid- filled cylinder with a piston and valving inside. The shock absorber's job is to provide a controlled amount of resistance every time the wheels bounce up and down or the chassis leans as it goes around a corner. SOLENOID A type of electrical device that uses an electromagnet to move something. The on the engine uses a solenoid for engaging the flywheel. Power door locks use solenoids to pull and release the locks. A fuel injector has a built-in solenoid that opens and closes the nozzle. SPARK PLUG A component in the ignition system that ignites the fuel inside the combustion chamber. The spark plug is nothing more than a pair of electrodes with a gap in between. When high voltage from the ignition system reaches the gap, an electrical arc jumps across it and ignites the fuel. SPRING A suspension component that supports the weight of the vehicle. Basic types include coil springs, leaf springs, air springs and torsion bars. Spring height affects ride height, which in turn affect wheel alignment. Weak or sagging springs should be replaced in pairs to restore and maintain proper ride height and wheel alignment.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 188 STATIC BALANCE Wheel balance that depends on an equal distribution of weight around the circumference of the wheel and tire assembly. Static balance can be achieved without spinning the wheel by using a bubble balancer. A wheel that lacks static balance will shake or tramp up-and-down. STEERING ARM The arms on the steering knuckles (or struts) to which the tie rods are attached to steer the wheels. STEERING DAMPER (STABILIZER) A hydraulic device similar to a shock absorber attached to the steering linkage to absorb road shock and steering kickback. STEERING GEOMETRY A general term used to describe the angular relationships between the wheels, steering linkage and suspension. SUSPENSION The part of a vehicle that carries the weight. This includes the springs, control arms, ball joints, struts and/or shock absorbers. TDC Abbreviation for Top Dead Center. This is the point at which the piston reaches its uppermost position in the cylinder. Ignition timing is usually expressed as so many degrees before top dead center (BTDC) or after top dead center (ATDC). A timing mark on the crankshaft pulley or flywheel corresponds to the top dead center position of the number one engine cylinder. THERMISTOR A device that changes electrical resistance as temperature changes. A coolant sensor and air temperature sensor are thermistors. THERMOSTAT A temperature control device in the engine�s cooling system that speeds engine warm-up and helps the engine run at a consistent operating temperature. Thermostats come in various temperature ratings must most engines today use ones that open between 190 and 195 degrees. (TPS) A little gadget on the carburetor throttle linkage or fuel injection throttle body that keeps the engine control computer informed about the throttle opening. The TPS is a variable resistor that changes resistance as the throttle opens wider. The computer needs this information to change the air/fuel mixture.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 189 TIE ROD A part of the steering linkage that connects the steering arms on the knuckles to the steering rack or center link. TIMING LIGHT A strobe light for checking ignition timing. The light is connected to the number one spark plug wire so every time the plug fires the light flashes. The light is then aimed at the timing marks on the crankshaft pulley or flywheel to read timing. TIRE ROTATION Changing the relative positions of the on a vehicle periodically to even out tread wear. Rotation is recommended every 5,000 km for optimum tire life. When tires are not rotated, they can develop wear patterns particular to their wheel location that shortens tread life and may cause vibrations or a rough ride. TOE A wheel alignment angle that refers to the parallelism of the tires as viewed from above (See Alignment). Toe-in means the leading edges of the tires are closer together than the rear edges. Toe-out means the leading edges of the tires are farther apart than the rear edges. A vehicle should have zero running toe (perfect parallel alignment) when driving. But because the rubber bushings and joints in the suspension "give" a little (called "compliance"), most rear-wheel drive vehicles call for a slight amount of toe-in when the wheels are initially aligned. Front- wheel drive vehicles are just the opposite, TOE-IN Toe-in means the leading edges of the tires are closer together than the rear edges. A small amount of toe-in is usually specified for rear-wheel drive vehicles to compensate for suspension compliance that allows the wheels to toe-out slightly as the vehicle is pushed down the road. Too much toe-in accelerates tire wear and causes the outside edges of the tread to wear more quickly. TOE-OUT Toe-out means the leading edges of the tires are farther apart than the rear edges. A small amount of toe-out is often specified for front-wheel drive cars to compensate for suspension compliance that allows the wheels to toe-in slightly when the front wheels pull the vehicle down the road. Too much toe-out accelerates tire wear and causes the inside edges of the tread to wear more quickly

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 190 TOE-OUT ON TURNS The change in toe that occurs when the wheels are steered to either side. The change in toe allows the inside wheel to follow a smaller circle than the outer wheel to reduce tire scuffing and wear. The toe angle is nonadjustable and is determined by the geometry of the steering arms and linkage. A toe-out on turn angle is usually specified for the outer wheel when the inner wheel is turned 20 degrees. If the angle is not within specifications, it usually means a steering arm is bent. TORQUE Turning or twisting force. Torque is usually expressed as so many foot/pounds (a one pound force exerted on a lever one foot in length). A torque wrench measures how much twisting force is being applied to a nut or bolt. The torque output of an engine is expressed as the maximum force exerted by the engine at a given engine speed. TORQUE CONVERTER A fluid coupling that connects the engine to an automatic transmission. The torque converter contains a three sets of bladed wheels that face one another. One wheel (the impeller) is attached to the converter housing and turns at the same speed as the engine. The other wheel (the turbine) is attached to the transmission input shaft. As the impeller spins, it slings automatic transmission fluid at the turbine, and makes it turn. The third wheel (the stator) is positioned between the turbine and impeller to redirect fluid flow. TORQUE WRENCH A special wrench with a built-in indicator that shows you how much force you are applying to a bolt. A torque wrench should always be used when doing any type of major engine work, when tightening fasteners on the brake system or suspension, when tightening wheel lug nuts or when you do not want to risk breaking a bolt. TORSION BARS A steel bar that is twisted to support the weight of the vehicle. Torsion bars are used in place of coil or leaf springs on some vehicles, and allow ride height to be adjusted to compensate for sage that occurs over time.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 191 TRACTION CONTROL An enhancement of an existing ABS system that prevents wheel spin while accelerating on wet or slick surfaces. It uses the same wheel speed sensors to monitor wheel speed during acceleration, but requires some additional control solenoids and a pump to apply braking pressure to control wheel spin. The traction control system brakes the that is starting to spin to shift torque to the opposite drive wheel that still has traction. TRANSAXLE The transmission in a front-wheel drive vehicle. It combines both transmission and differential into one assembly. TRANSISTOR An electronic component using a semiconductor to amplify or switch current. Used in voltage regulators, computers and other electronic accessories. TRANSMISSION The gear box that multiplies engine torque via gear reduction and/or torque conversion. A typical manual transmission has four or five speeds, with the final or highest gear being either a direct 1:1 drive ratio or an "overdrive" ratio (less than 1:1). An automatic transmission first multiplies engine torque as it passes through the fluid coupling known as the "torque converter" and then through three or four separate gear ratios. A manual transmission usually gives slightly better fuel economy than an automatic because there is a certain amount of slippage that occurs in the automatic torque converter. TUNE-UP An obsolete term used to describe the periodic maintenance that is performed when "tuning" an engine to its original specs. With electronic ignition systems that require no periodic adjustments, sealed carburetors and non-adjustable fuel injection, there is not much left to adjust.

TURBOCHARGING A means of increasing horsepower (up to 50 percent or more) by using an exhaust-driven air pump (the turbocharger) to force more air and fuel into the engine. Hot exhaust gases coming out of the engine spin an impeller on one end of the turbocharger. On the other end is a second impeller that pumps air into the engine. A "wastegate" (a small trap door that opens to bleed off exhaust pressure) limits the amount of pressure boost the turbo can produce.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 192 TURNING RADIUS The diameter of the smallest circle in which a vehicle can complete a U- turn. Turning radius depends on the wheelbase of the vehicle (longer vehicles usually need more space to turn around), and maximum steering angularity. U-BOLT A bolt in the shape of a "U" that attaches an axle housing to a leaf spring. UNDERSTEER A steering condition where the vehicle does not respond quickly to steering changes. If a vehicle understeers, it wants to continue going straight when the steering wheel is turned. Under normal driving conditions, understeer is not a problem. But when the vehicle is driven at high speed into a curve, the front of the car will tend to plow to the outside. UNIVERSAL JOINT Another name for a Cardan joint (See Cardan Joint). V-BELT More commonly known as a "fan belt," a V-belt is the rubber belt that drives such things as the alternator, air conditioning compressor, power steering pump and waterpump. It is called a V-belt because of its "V" shaped cross-section. The sides of the belt are what grip the pulleys. Some belts have notches in them to increase grip, to help cool the belt and to relieve stress as the belt bends around small diameter pulleys. VACUUM The absence or reduction of air pressure. Vacuum is created in the intake manifold by the pumping action of the pistons. Air is pulled out of the manifold into the cylinders faster than it can be replenished by air bypassing the throttle plate. The throttle creates a restriction that allows vacuum to buildup inside the manifold. This is necessary to help pull fuel through a carburetor, and to vaporize fuel sprayed into the engine by fuel injectors. VACUUM ADVANCE When an engine is cruising under light load, there is very strong vacuum in the intake manifold. This pulls on the vacuum advance diaphragm and advances timing for better fuel economy. When the engine is under heavy load, the throttle is opened wide and vacuum falls. This releases the diaphragm and eliminates the extra timing advance. Where the extra advance not canceled, the engine would likely experience spark knock.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 193 VAPOR LOCK When gasoline overheats and boils inside the carburetor bowl or fuel pump of a hot engine, it ceases to flow. This can cause stalling or hard starting. This is called vapor lock, and it usually happens during hot weather. If a hot engine will not start, all you can do is let it sit and cool off. VARIABLE VALVE TIMING (VVT) A method that advances or retards camshaft timing to improve engine performance. A hydraulic mechanism on the cam drive uses oil pressure to rotate the cam’s position slightly as engine speed changes. This increases valve duration to produce more horsepower at higher rpms. VISCOSITY This is a term used to describe the thickness of . The higher the number, the thicker the oil. Common straight grade viscosity ratings are 10, 20, 30 and 40, with 10 being the thinnest and 40 the thickest. A low viscosity oil provides better lubrication at low temperatures and reduces internal drag on the engine VOLTAGE REGULATOR A part of the charging system that controls how much electricity the alternator puts out (See Alternator). The voltage regulator on today's cars is an electronic black box, which means you cannot adjust it or repair it if anything goes wrong with it. On most newer vehicles the voltage regulator is located inside the alternator and cannot be replaced separately. WATER PUMP A small impeller-like pump that circulates coolant through the engine's cooling system. The waterpump is mounted on the engine and is driven by the fan belt, alternator belt or overhead cam timing belt. WHEEL BALANCE The even distribution of weight around a wheel so that it rotates without vibrating or shaking. See static and dynamic balance. It is achieved by positioning weights on the rim that offset heavy spots on the wheel and tire assembly. WHEELBASE The distance between the centers of the front and rear wheels. Measuring and comparing the wheelbase on both sides of a vehicle can identify rear axle misalignment or front wheel setback.

Reproduced by Speciss College with permission from Chris Longhurst www.carbibles.com 194 WHEEL BEARINGS Inside the wheel hubs are either roller or ball bearings that carry the vehicle's weight. On RWD vehicles with solid axles, the rear wheel bearings are mounted on the axles. The front wheel bearings on older rear-wheel drive cars and trucks usually require "repacking" (regreasing) every two years or 20,000 km. The wheel bearings on most newer vehicles are sealed and do not require any maintenance. WHEEL CYLINDER This is the hydraulic component that pushes the brake shoes out in a drum brake. The wheel cylinder consists of a small casting with two outward facing pistons. When hydraulic fluid from the master cylinder is forced into the cylinder, it pushes the two pistons out and applies the brakes.

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