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Journal of the Department of Agriculture, Western Australia, Series 3

Volume 3 Number 2 March- April,1954 Article 3

3-1954

The farm tractor, part.1 - how the works

Follow this and additional works at: https://researchlibrary.agric.wa.gov.au/journal_agriculture3

Recommended Citation (1954) "The farm tractor, part.1 - how the engine works," Journal of the Department of Agriculture, Western Australia, Series 3: Vol. 3 : No. 2 , Article 3. Available at: https://researchlibrary.agric.wa.gov.au/journal_agriculture3/vol3/iss2/3

This article is brought to you for free and open access by Research Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 3 by an authorized administrator of Research Library. For more information, please contact [email protected]. : //;W»«!«

Part 1.-How the Engine Works TVTO driver can look after his tractor properly unless he knows something of the ll way it works. The modern tractor is a sturdy machine designed to stand con­ tinuous hard work, but it contains a certain amount of complicated mechanism. All drivers, therefore, should know enough of the working principles of a tractor to be able to undertake the "maintenance" of the one they use.

If through neglect or ignorance a tractor therein may be rather too detailed and too does not get proper maintenance— technical for the new-comer to tractor 1. It will never be capable of under­ work to grasp at all readily. Moreover, taking its full duty. there is an instruction book for every single 2. Repair bills will be heavy. model, and the maintenance instructions given for one are not always a safe guide 3. It will break down, generally at busy to the maintenance of another. These times. articles have been written, not to replace 4. Its working life will be considerably the instruction book, but to give beginners shortened. in particular, and even in some cases "old hands," an insight into the construction 5. Fuel will be wasted. and use of tractors in general. Thus they In the long run the only complete guide may more easily understand the detailed to the maintenance of a tractor is the instructions given by the makers of the instruction book issued by the makers. The tractor they have to operate. instruction book is the most valuable part of the tool-kit supplied with a new tractor. THE INTERNAL COMBUSTION ENGINE The kind of engine used in a tractor is called an internal combustion engine be­ The letterpress and illustrations in this cause it converts the heat energy of fuel series of articles are from a handbook into mechanical work by burning the fuel prepared by the National Institute of inside the engine itself. Agricultural Engineering (England) A , for example, is not an and are reproduced by courtesy of the internal combustion engine because the Institute and the British Ministry for engine part of it—, and so Agriculture and Fisheries. on—is quite distinct and separate from the fire-box in which the fuel is actually burnt. The fuel burnt in an I.e. engine can be any one of the following:—Coal or pro­ Any owner who has no instruction book ducer gas, petrol or kerosene vapour, or for his own particular model would do well diesel oil in the form of a finely-atomised to order one. But the information given spray. 133 Journal of agriculture Vol. 3 1954 The general principle of all I.e. THE SINGLE CYLINDER FOUR- is the same and depends on the fact that ENGINE air combined in the right proportion with The cycle of operations is shown in Fig. 2. any one of these fuels will form an ex­ plosive mixture. The various types of 1. Induction Stroke. engine differ from one another only (a) The inlet valve opens. according to the fuel used, the exact arrangements for introducing and explod­ (b) The piston moves down the cylinder. ing it, and the number of cylinders. For (c) Fuel and air mixture is sucked into tractors the most common and important the cylinder. type is the four-stroke engine starting on (d) When the piston reaches the bottom, petrol and running on a special kind of the cylinder is full of explosive mixture and kerosene known as vapourising oil. the inlet valve closes. 2. Compression Stroke. Fig. 1 shows a diagram of a four-stroke I.C. engine cut across the middle, and (a) Both valves are closed. viewed from the end. All the most import­ (b) The piston rises. ant parts are labelled, and will be referred (c) The mixture in the cylinder is com­ to throughout this book by these names. pressed into a much smaller space.

Sparking Plug

CYLINDER HEAD VALVE

Valve Guide Compression Rings

INLET or EXHAUST PORT

CONNECTING ROD

CRANKCASE

Big End

" ' XCrankshafr Timing Gear

SUMP FIG. I THE 4-STROKE ENGINE 134 Journal of agriculture Vol. 3 1954 ^THm£tse th,s §

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INDUCTION STROKE COMPRESSION STROKE

EXHAUST •

FIRING STROKE FIG. 2 EXHAUST STROKE

3. Firing Stroke. 4. Exhaust Stroke. (a) At the end of the compression stroke (a) The exhaust valve opens as the both valves are still closed. piston reaches the bottom of the firing (b) As the piston reaches the top of this stroke. stroke a spark at the sparking plug ignites (b) The piston moves up the cylinder the compressed mixture. again. (c) The force of the explosion of that (c) The burnt gases are driven out past mixture drives the piston down the the exhaust valve. cylinder. (d) The exhaust valve closes. \ 137 Journal of agriculture Vol. 3 1954 Then once more the inlet valve opens— or 1-2-4-3 depending on the make of the fresh mixture is drawn into the cylinder tractor. The more common is 1-2-4-3: but and the whole cycle starts over again. the will usually be found An engine of this kind is called a four- marked somewhere on the engine. A four- stroke engine because, as indicated above cylinder engine runs smoothly and gives there are four strokes of the piston for a fairly uniform output of power because, each explosion. The explosion stroke is whatever the position of the crankshaft, the only working stroke, i.e., the only one one or other of the is actually on in which the piston drives the crankshaft. the firing or "working" stroke. During the remaining three strokes of the cycle the crankshaft continues to turn PETROL STARTING FOR TRACTORS round because of the momentum of the RUNNING ON VAPOURISING OIL . Most tractors in this country use vapour- ising oil (kerosene) as fuel because it is THE FOUR-CYLINDER ENGINE relatively cheap. But a tractor cannot be Smoother running and a more uniform started from cold on vapourising oil be­ output of power will obviously result from cause this fuel will not turn into vapour using several cylinders with the corres­ until it has been warmed up. For this ponding pistons all coupled to the same reason all vapourising oil tractors are crankshaft as indicated in Fig. 3. started on petrol and should be run on petrol until their engines are hot enough The vast majority of tractor engines have four cylinders working on the above prin­ to vapourise the normal fuel properly. ciple, i.e., they have what are called four- cylinder four-stroke engines. In such an OTHER KINDS OF TRACTOR ENGINE engine one cylinder fires for each stroke: In America petrol is cheaper than it is that is, two cylinders fire during each com­ here so it is more often used as a tractor plete revolution of the crankshaft and fly­ fuel. A petrol-air mixture can be more wheel. The order of firing in a four- highly compressed than a vapourising oil- cylinder four-stroke engine is either 1-3-4-2 air mixture without giving trouble on the

SPARKING PLUGS

CYLINDERS CYLINDERS

PISTONS

VALVES

CONNECTING ROD

FLYWHEEL

CRANKSHAFT

FIG. 3 THE 4-CYJJNDER ENGINE 138 Journal of agriculture Vol. 3 1954 INDUCTION STROKE COMPRESSION STROKE

FIRING STROKE FIG. 4 EXHAUST STROKE

THE DIESEL CYCLE firing stroke: or, as we generally say, an THE engine running on petrol can have a higher In some parts of the world vapourising than an engine running oil is either expensive or difficult to obtain, on vapourising oil. With a higher com- and the only cheap fuel is diesel oil. In pression ratio more power can be obtained those places tractors with diesel engines from the same size of engine, and so, if it are popular; some tracklaying tractors of has been specially designed for the purpose, this type are also to be found in this a will generally be more country. The diesel engine works on the powerful than a vapourising oil engine of same principle as the vapourising oil the same size. engine, but there is no sparking plug and 139 Journal of agriculture Vol. 3 1954 fuel is not introduced until the end of the tend to spring outwards and so project compression stroke (see Fig. 4). The cycle slightly from the piston and press against is as follows:— the cylinder wall. 1. Induction Stroke.—The inlet valve The connecting rod is connected to the opens—the piston goes down, drawing in piston by the gudgeon pin, which passes pure air—the inlet valve closes. through the little-end bearing in the con­ necting rod and is supported at each end 2. Compression Stroke.—Both valves are in the wall of the piston. The end of the closed—the piston comes up and com­ connecting rod attached to the crankshaft presses the air in the cylinder. The engine is called the big-end bearing and is in two has a high compression ratio and on this parts bolted together round the crankshaft. stroke the air is compressed so much that it get hot—as it does in a pump The crankshaft, like the pedal and when a tyre is being inflated. of a bicycle, turns the up-and-down motion of the piston into rotary motion, which can 3. Firing Stroke.—As the piston reaches be used to drive the tractor wheels. The the top of the compression stroke a spray crankshaft itself is carried in bearings of diesel fuel is shot into the cylinder known as main bearings—in a four- through a nozzle called an injector. The cylinder engine there can be two, three or heat of the compressed air is sufficient to five main bearings, three being most com­ ignite the fuel, causing an explosion which mon. drives the piston down. The valves are generally of the poppet or 4. Exhaust Stroke.—The exhaust valve mushroom type consisting of a mushroom- opens and as the piston comes up the burnt shaped head on a central stem. They move gases are driven out of the cylinder. The exhaust valve then closes and the cycle Piston Rings starts again by drawing in fresh air. Most four-stroke diesel en­ Piston gines can be started from cold but their high compression ratio makes them difficult to turn by hand, and they often Crankshaft have auxiliary starting de­ Timing Gear vices. Thus some diesel- engined tractors have a small petrol engine for starting them, while others are ar­ ranged so that they can start on petrol, and operate as ord­ Pulley inary petrol engines until Main Bearings they warm up.

TRACTOR COMPONENTS FIG. 5 THE CRANKSHAFT This section aims at show­ ing how the principles of the internal up and down in "sleeves" called valve combustion engine are put to practical use guides and are held in the closed position in a tractor. by valve springs. There are two common arrangements—side valves and overhead valves as shown in Fig. 6. Practically all THE TRACTOR ENGINE tractors, except the Fordson, have over­ The piston must make a gas-tight joint head valve engines. In tractors, overhead with the inside wall of the cylinder and valves are operated by push rods from a yet be free to move up and down. This camshaft at the side of the engine. gas-tight fit is obtained by three or more cast-iron rings (piston rings) which are let The Camshaft.—The valves are opened into grooves around the piston. The rings and closed at the correct times by means 140

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Journal of agriculture Vol. 3 1954 ourises, i.e., turns into gas. up from the jet rapidly vap- Such a mixture of air and petrol vapour explodes easily. Vapourising oil does not turn into gas unless it is heated. It leaves the jet as a very fine spray made up of small drops of fuel, which must then be heated in a vapouriser to turn them into gas.

Pujh Rod The vapouriser is a narrow box, one side of which is heat­ ed by the hot gases leaving the engine on each exhaust stroke. When the engine has

• been running for a short time on petrol the vapouriser becomes hot. If the engine is then turned on to vapourising oil, the spray of fuel from the SIDE VALVE OVERHEAD VALVE jet will be heated and turned FIG. 6 into a gas, which forms with air an easily exploded mix­ ture (see Fig. 8). of , which are merely projections from the camshaft. The setting of the camshaft is of great importance in the MIXTURE running of the engine. On this will depend the valve timing, that is, the exact moments at which the valves FUEL FROM TANK open and close.

The Carburettor.—As the piston descends, a stream of air is drawn over a small hole called the jet from which it picks up some fuel and carries it on into the cylinder. The jet is fed from the JET through a fuel chamber con­ taining a float. If more fuel enters the float chamber than the engine needs, the float will rise until the valve at the top closes the pipe from the tank. When the engine needs CHOKE more fuel, the float will fall VALVE and allow more to enter the float chamber. The quantity of fuel reaching the jet is FLOAT CHAMBER controlled by the setting of a needle valve (see Fig. 8). AIR

The Vapouriser. — When petrol is used, the fuel picked FIG. 7 THE CARBURETTOR 143 Journal of agriculture Vol. 3 1954 EXHAUST GASES CHOKE VALVE that the engine tends to speed up, the governor closes the VAPORISED and cuts down the FUEL AND AIR fuel supply. The produces the spark at the sparking plug which fires the mixture in the cylinders. It is a small FUEL dynamo and induction (or "shocking") coil combined. When the end cover is taken off, the inside will look some­ thing like the diagram in Fig. 9. This shows the moment at which a spark is produced at the sparking plug in No. 1

NEEDLE VALVE cylinder. A spark is produced whenever the points of the EXHAUST PIPE open, which occurs each time the end of the passes the FIG. 8 THE VAPORISER cams on the stationary ring. The spark appears The Throttle is shown in Figs, 7 and 8. It at No. 1 plug because the rotor arm is a flat disc of metal which can be set so of the is passing the end that it partially blocks the induction pipe, of No. 1 plug-lead. In the magneto shown, i.e., the pipe along which the fuel-air mix­ this rotor arm is geared to revolve at half ture flows to the engine. The speed and the speed of the contact breaker, so that power of the engine are controlled by the when the points next open the rotor arm amount of mixture that the throttle allows of the distributor will be opposite No. 2 to enter the cylinders. In Fig. 7 the throttle pluglead. The magneto must be "timed" is open, in Fig. 8 it is closed. so that the points open, i.e., the spark The Choke.—The engine requires a "rich occurs, in the right cylinder and at the mixture" for starting, i.e., more petrol right time in relation to the position of the vapour in the mixture than is needed for piston at the end of each compression normal running. For this reason another stroke. disc, similar to the throttle, is placed in A Sparking Plug is the means whereby the air so that the air has to flow the mixture is ignited in the cylinder by a past it before reaching the jet. Normally spark appearing at the gap between its this disc—called the choke—is wide open, points. Sparking plugs must be kept clean but for starting it is partially closed to and in good order or the spark they give restrict the flow of air and make the mix­ will be weak. In that case the mixture will ture rich in petrol. It is shown in the two not be ignited properly: starting will be diagrams—in the top one it is open for difficult and power will be lost. normal running and in the bottom one it It is most important, therefore, that is partially closed for starting, i.e., the plugs should be taken out periodically and engine is "choked." cleaned thoroughly. The Governor is an automatic device Not all sparking plugs are alike, and, which keeps the engine running at the whenever possible, the particular type of same speed whether the load is heavy or plug recommended by the makers of a light. The governor control allows the tractor should be fitted. driver to alter the speed at which the The Impulse is a device which governor keeps the engine running. If makes tractors easier to start. When the load on a tractor increases so that the turned slowly a magneto gives a weak spark engine speed tends to fall, the governor that makes starting difficult, so while the opens the throttle and gives the engine engine is being turned slowly some means more fuel. When the load decreases so has to be found to increase the magneto 144

Journal of agriculture Vol. 3 1954 SPARKING PLUGS

TERMINAL NUT \

INSULATOR

POINT

ROTOR ARM DISTRIBUTOR

POINT ADJUSTMENT

CAM RING

CONTACT BREAKER

— ROCKER ARM

FIG. 9 THE MAGNETO

145

Journal of agriculture Vol. 3 1954 speed. When the engine is turned the im­ 2. Pressure Feed.—Oil drawn from the pulse starter prevents the magneto from through a screen is pumped through turning with it until the piston reaches pipes to every part of the engine (see Fig. the top of the compression stroke. At this 10). moment the magneto is released, and is driven round at high speed by a spring so 3. Force Feed and Splash is a combina­ that it delivers a "fat" spark. The spark tion of the above. Usually the big-ends, thus produced by hand-turning is as good little-ends and piston are lubricated by as the spark delivered in normal running splash and the rest of the engine by a at normal engine speed. The impulse pump feed. starter engages automatically when the Few tractors nowadays have splash lub­ engine stops and can be heard to "click" rication systems. Most of them are wholly as the engine is turned over by hand. As or partly pressure fed and a gauge is fitted soon as the engine starts it disengages to show that oil is circulating. This should itself automatically. Any modern tractor be watched during work and the engine can therefore be started simply by pulling stopped at once if no pressure is showing up the starting handle. on the dial. In addition, an oil Alter may be fitted to keep the oil free from con­ The Lubrication System can be one of tamination. This filter should be cleaned the following:— or replaced periodically as the makers 1. Splash.—The big-ends dip into trays advise in the instruction book. carrying oil in the sump, and so cover the The diagram (Fig. 10) shows a typical inside of the engine with oil. pressure-fed lubrication system. After

FEED TO OVERHEAD VALVE GEAR OIL PRESSURE GAUGE

FILTER

VALVE V_/

TIMING GEARS

OILWAY DRILLED IN CRANKSHAFT

SCREEN DRAIN PLUG

FIG. 10 A FORCE FEED LUBRICATION SYSTEM 146

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Journal of agriculture Vol. 3 1954 being pumped through a filter the oil is top of the radiator. The radiator is a carried by pipes to the various bearings, series of tubes with fins, through which reaching the big-ends through oil-ways air is drawn by the fan. As the water is drilled in the crankshaft. In the drip feed cooled in the radiator it becomes heavier, to the overhead valve gear, the oil finds falls to the bottom and passes to the its way down the push rods and to lower part of the cylinder jacket, to re­ lubricate the cams before returning to the place the warm water leaving at the top. It is usual on tractors to have

HOT WATER a pump or impeller at some point in the circuit to assist the circulation and improve the efficiency of the cooling. In practice, tractors run­ ning on vapourising oil tend to keep cool, especially on light loads. In a cool engine the fuel is not completely vapourised, with the result that maximum power is not developed and unburnt fuel passes the pistons to the lub­ ricating oil in the sump with COOLINC flNS harmful effect. There are three main methods of con­ trolling the engine temper­ ature:— AIR 1. Radiator blinds. 2. Radiator shutters. 3. A control­ ling the pump circulation. COOL WATER 1 and 2 are most satisfac­ tory when used in conjunc­ tion with a thermometer, FIG. II RADIATOR SECTION which can be read from the sump. Lubrication of the A cylinder walls and little-ends is effected by splash from the crankshaft and by oil-mist.

The Cooling System.—An internal combustion engine, with its large number of ex­ plosions per minute in each cylinder, needs some cooling device to prevent damage by excessive heat. Water is used, and the usual method of cooling is by the thermo- syphon system. In this sys­ tem the water circulates be­

cause hot water is lighter COOL WATER than cold. Hot water from the parts of the engine near­ FIG. 12 est to the cylinders rises and passes through a pipe to the THE COOLING SYSTEM 149 Journal of agriculture Vol. 3 1954 drivers seat. The thermometer is best raised to keep the engine warm for fitted near the top of the radiator, where starting or during cold weather^ and the water should be kept just under boil- periods of light foaSng, 7ndlowered mg pomt. Radiator blinds can be for warmer weather or heavy Toads

PTO AND PULLEY DRIVE PULLEY

REAR AXLE HALF SHAFT DIFFERENTIAL

FIG. 13 THE TRANSMISSION SYSTEM 150

Journal of agriculture Vol. 3 1954 Radiator shutters are opened and closed are known as dry clutches. The multiple by a hand lever from the operator's seat. plate clutch consists of a number of plates, Some tractors use a valve called a ther­ half which are driven by the engine and mostat which is fitted between the top of half fixed to the shaft driving the gearbox. the cylinder and the radiator. When the These plates are arranged alternately—one water round the cylinders is hot enough, engine driven, then one that drives the this valve opens and allows the water to gearbox and so on. When the clutch pedal flow to the radiator for cooling. is depressed the plates are allowed to spread, so that they do not touch and drive each other. In the same way when the THE TRANSMISSION SYSTEM pedal is released the clutch springs clamp The transmission system of a tractor is the plates together, and the engine drives divided into three parts:— the gearbox. Multiple plate clutches are 1. The Clutch may be one of two usually fitted in a part of the transmission to which the engine oil can penetrate and types:— thus, running in oil, are known as wet (a) Single plate. clutches. (b) Multiple plate. The single plate clutch is the more com­ 2. The Gearbox gives a choice of tractor mon in modern tractors. It consists of one speeds so that the power of the engine plate held tightly between two surfaces by may be used to the best advantage, and powerful springs. One of these surfaces the speed chosen for each farming opera­ is usually on the engine flywheel, the other tion. The gearbox is designed to allow gear is attached to the shaft which drives the changes only when the tractor is station­ gearbox and back axle. Pressing on the ary, and the gears should not be changed clutch pedal, parts these two surfaces so while the tractor is moving. that the plate is free, and the gearbox is 3. The Back Axle is the final drive from no longer driven by the engine. Releasing the gearbox to the rear wheels. It con­ the pedal allows the clutch springs to sists of two half shafts and a differential clamp the plate between the two surfaces, gear which enables the driving wheels to and so to connect the engine to the gear­ turn at different speeds when going round box. Single plate clutches are fitted in a corners. separate compartment in the transmission system where no oil can reach them and (To be continued)

BEEHIVE REGISTRATION that re-registration fell due on January 1, HE Director of Agriculture (Mr. G. K. 1954. T Baron Hay) wishes to remind all bee­ In applying for registration or re- keepers that under the Bees Act, 1930- registration, beekeepers should forward 1950, any person keeping bees must be the full name, address, and particulars of registered for the current year, the period location. Country applicants should add of registration ending on December 31, exchange to cheques drawn on country annually. bank branches. Persons owning hives of bees who have not previously registered are required to pay a registration fee of 2s. 6d. for any number of hives up to 25. A further fee of Is. should be paid for each additional 25 hives or lesser numbers in excess of the first 25. Persons registering for the first time as beekeepers are also required to take out a registered brand for which a further fee of 7/6 is payable. Beekeepers who have previously regist­ ered must re-register and are reminded 151 \ Journal of agriculture Vol. 3 1954 THE MOST EFFICIENT

BRAND OF PHENOTHIAZINE WORM DRENCH

INFESTATION OF YOUR SHEEP WITH EVEN SMALL NUMBERS OF PARASITES CAN REDUCE THEIR APPETITE BY 50% AND CAUSE LOSS OF WOOL PRODUCTION AND GROWTH.

WORMY SHEEP Eats only 3 lbs. Grass daily. Mtw~\r~\i

HEALTHY SHEEP Eats 5 lbs. Grass daily.

Don't let worms starve your sheep. Obtain your highest return from worm free sheep. Drench with 'PHENOVIS'.

•JL One of a series of advertisements designed to convey as a

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published in the Australian Veterinary Journal and elsewhere.

IMPERIAL CHEMICAL INDUSTRIES OF AUSTRALIA & NEW ZEALAND LIMITED ALL CAPITAL CITIES

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Journal of agriculture Vol. 3 1954