TECH GUIDE 1 1-5 Gaskets/Decks 4/15/09 10:51 AM Page 2

2009 APRIL

Pg 1 Head & Block Decks & Gaskets Pg 6 Cylinder Bores & Piston Rings Pg 12 Valves & Valve Seats Pg 16 Cam Bores, Bearings & Camshafts or more information

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ince the days of sealing Smooth Operation or chatter when it makes an interrupt- engines with asbestos, cork, How smooth is smooth enough? You ed cut. S rope and paper are, for the used to be able to tell by dragging For example, a converted grinder most part, ancient history, your fingernail across the surface of a may be able to mill heads and blocks. new-age materials and designs have cylinder head or engine block. And But the spindles and table drives in elevated the critical role gaskets and besides, it didn’t really matter because many of these older machines cannot seals play in the longevity of an the composite head gasket would fill hold close enough tolerances to engine. Finding the optimum sealing any gaps that your equipment or tech- achieve a really smooth, flat finish. material and design remain a chal- nique left behind. One equipment manufacturer said lenge many gasket manufacturers face But with MLS gaskets the require- grinding and milling machines that as engines are asked to do more. ments have changed. To seal properly, are more than five years old are prob- Gaskets that combine high per- a head gasket requires a surface finish ably incapable of producing consistent formance polymers with metal or that is within a recommended range. results and should be replaced. fiber substrates are being used in more This range varies depending on the Most of the surfacing equipment and more engine applications. type of gasket.Too rough (or in some that’s being sold to shops today has Furthermore, engines that are sealed cases too smooth) and the gasket may been redesigned for high speed using these higher quality gaskets are not seal properly and leak or fail. milling with CBN and PCD. The lasting longer, performing better and According to surfacing experts, the machines have been beefed up with with less maintenance or chance of recommended surface finish for a tra- more powerful motors, heavier cast- the dreaded warranty comeback ditional composite-style soft-face ings, electrically driven ball screw claim. head gasket in an engine with cast tables, and tighter assembly tolerances. There are many considerations iron heads and block is 60-120 Some can hold machining tolerances engine builders must take into microinches Ra (roughness average). to .0001˝! account when selecting the best gas- The recommended finish for the same Doing the job right may be more kets for an application. With engines head gasket with an aluminum head challenging than ever, but doing the having higher performance require- on a cast iron block is typically 20-50 job wrong may cost you even more. ments, stricter emission regulations, microinches Ra. and tighter design tolerances along For engines with MLS gaskets, the Head Gasket Evolution with production cost considerations OEM surface finish recommendations The cylinder head gasket is arguably and quality standards that are increas- are even smoother, perhaps 20-30 or the most important seal in the engine. ing, the last thing any engine builder even 7-15 Ra. Since the very first internal combus- wants to worry about is a gasket or Accurately measuring the surface tion engines were produced, gasket seal failure. finish can be done using a profilome- designers have specified many materi- It doesn’t matter if you’re building ter, an electronic instrument that drags als to meet this difficult sealing chal- a Pro Stock or stock production a diamond-tipped stylus across the lenge. engine: the risks are simply too great surface to calculate its profile charac- to use a subpar gasket or seal. teristics. The profilometer then shows Three Types of Head Gaskets It’s more complicated to seal today’s various values for the surface includ- Composite – this technology is engines because, depending on the ing roughness average (Ra), average used mostly on older stock engine application, modern engines are peak height (Rpk), average valley applications and in some performance expected to last well over 150,000 depth (Rvk) and even waviness. applications. Typically these types of miles without fail. Performance These critical surface finishes gaskets are made from graphite and engines are pumping out more power require high quality resurfacing equip- can be more prone to blowouts than than ever. So keeping these engines ment to achieve low Ra numbers. MLS gaskets. In the aftermarket, com- sealed can be a tall order and creates a Extremely smooth finishes require posite gaskets are still required for hefty job for engine gaskets and seals high quality resurfacing equipment to many older applications and are also to handle. achieve really low Ra numbers. It more forgiving of less than perfect Engine seals and gaskets are sup- doesn’t matter if you use carbide, surface finishes. posed to prevent the leakage of oil, cubic boron nitride (CBN) or poly- Copper - A solid sheet of copper coolant and air between mating sur- crystalline diamond (PCD) tool bits to typically requires machining for O- faces, internal passages and the outside resurface a head as long as you use the rings that place a piece of wire around of the engine. Seals and gaskets also correct feed rate and speed – and the the circumference of the cylinder to prevent the entry of dirt and air into equipment is rigid enough to hold the bite into the copper.When used with the engine. cutter steady so the tool bit doesn’t lift O-rings, copper gaskets are extremely

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durable. Copper gaskets are mostly and is unmatched by any other sealing als are taking the place of older, less used in performance applications system to this point.Today,it is rough- compatible and less durable materials. where there is a lot of cylinder pres- ly estimated that 80 percent of new The following list shows the types of sure. Recently some gasket companies engines are designed with MLS gas- materials used in automotive applica- have started producing copper gaskets kets as standard equipment and further tions and the characteristics of each with integral sealing wires permitting growth is projected. type. their retrofit into engines without the In the MLS gasket, multiple thin Viton – Viton is a registered trade- need to machine the engine block. layers of cold-rolled spring grade mark of DuPont Performance Copper and brass gaskets were stainless steel are coated with 7-25 Elastomers and is commonly called some of the earliest materials used but microns of elastomeric material. The Fluoroelastomer/ Viton (FPM). It is gave way to metal and asbestos com- resilient elastomer is essential to the best known for its ability to tolerate posite gaskets in the 1950s, superseded structure by providing micro-sealing high temperature environments in turn by composite metal and of metal surface imperfections while (400°F), which makes it well suited for impregnated fiber or graphite com- resisting aggressive combustion gases, automotive applications. posites by the 1980s. However, those oils and coolants at temperatures up to Viton can also easily withstand systems were largely overtaken by the 250°C or 480° F. aggressive fuels and chemicals and has development of the Multi-Layer Steel excellent mechanical properties as (MLS) gasket in Japan during the early Better Sealing well. This material is also resistant to 1990s. Through Chemistry abrasion and cuts. With a broad array Multiple Layer Steel (MLS) – Gasket manufacturers use all kinds of of applications in the automotive, this type of head gasket typically con- materials and designs to keep engine chemical processing and industrial sists of three layers of steel. Most mod- oil, coolant, vacuum and compression markets,Viton fits many performance ern engines today are produced with separated from each other. Through specifications. MLS gaskets. The contact layers are the use of computer aided design Neoprene Polychloroprene – usually coated with a rubber-like (CAD), finite element analysis (FEA) Neoprene polychloroprene was the first coating such as Viton that adheres to and polymer science, gasket engineers synthetic elastomer able to resist oil and the cylinder block and cylinder head can now more thoroughly understand is still a popular material in a number of respectively while the thicker center many facets of the joint they are try- automotive applications. Neoprene layer is bare, allowing for movement as ing to seal and are able to design a gas- remains a popular choice for many if it were like a spring. ket with materials that will withstand automotive applications that require a MLS gaskets remain the automo- the pressures of the environment. reasonably priced, mid-performance tive industry’s preferred method of Materials such as Teflon, Viton, polymer with a good all-around bal- sealing the cylinder head and block, Graphite and other specialized materi- ance of performance properties.

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Nitrile (NBR) – NBR provides excellent resistance to mally from minus 100°C to plus 250°C (212° to 482° F). petroleum oils and gasoline as well as mineral and vegetable When compared to natural rubbers, silicone has better fire oils. However, NBR has poor resistance to the swelling resistant properties and is an excellent electrical insulator. action of oxygenated solvents such as acetone and ketones. Thermal stability means that properties such as volume It has good resistance to acids and bases except those hav- resistivity, dielectric strength and power factors are not ing strong oxidizing effects. Resistance to heat aging is affected by changes in temperature. good, which is a key advantage over natural rubber. Fluoroelastomer – FKM has been utilized by much of Higher acrylonitrile contents increase solvent resistance the European OEs and is the most successful coating mate- but decrease low-temperature flexibility, and compounding rial for long-term functionality critical sealing environ- this material to improve low-temperature flexibility ments such as automotive engines.Although nitrile rubber decreases oil and solvent resistance. This material does not (NBR) has been widely used for MLS coatings in the US crystallize on stretching and reinforcing materials are and Japan, the use of FKM is expected to grow rapidly required to obtain high strength.With compounding, it is among the OEs in both of these markets in next few years. possible to get a good balance between low creep, good resilience, low permanent set and good abrasion resistance. Head Gasket Failures Tear resistance and electrical insulation properties of NBR With most OEMs choosing to use aluminum rather than are inferior to natural rubber. iron cylinder heads, the chance of a head gasket failure is Silicone Rubber – Silicone rubber offers stability over increased. Even though aluminum is lighter than iron, it has a wide temperature range, resistance to harsh environ- a much greater thermal expansion rate, which in turn cre- ments, and long lasting performance exceeding many ates more stress on the head gasket. Engine manufacturers organic elastomers. Silicone rubber offers incredible resist- have responded to this by adding a non-stick coating such ance to extreme temperatures, being able to operate nor- as Teflon or some other type of slick coating to the surface of the head gasket. Most engine builders know that when a head gasket fails, a whole range of problems can occur, from compression loss to exhaust gases being forced into the cooling system, leading to the engine overheating and increased engine wear due to the oil being mixed with antifreeze. Coolant can leak into the cylinders, causing the exhaust to blow off steam and the steamy coolant mixture can damage the catalytic converter. If a very large amount of coolant does this, hydrolock can occur, causing extensive engine damage. Sometimes, all that may happen when a head gasket is blown is an eruption of steam from the tailpipe, though the engine may act and drive like normal. If your customer suspects a blown head gasket you or your installer can investigate the sit- uation by checking the compression with a pressure gauge, but the preferable method is a leak-down test, noting any indication of combustion gasses in the cooling system. Oil mixed with coolant and excessive coolant loss with no apparent cause, or presence of carbon monoxide or hydrocarbon gases in the expansion tank of the cooling system can also be signs of head gasket problems. Intake Manifold Gaskets The head casting-to-intake manifold joint is critical because if you experience a failure it will create a vacuum leak which will in turn Circle 104 for more information 4 PERFORMANCE PARTS & MACHINING TECH GUIDE | April 2009 1-5 Gaskets/Decks 4/15/09 10:51 AM Page 5

create a poor running engine and an thermostat housings, etc. Cut gaskets grommets for lining up the holes and unhappy customer. are also the least expensive to make metal carriers to make the gasket It is recommended that you check and allow the OEMs to use stamped stiffer so it won’t flop all over when the head and manifold sealing surfaces steel valve covers, timing covers and you try to line everything up. with a straightedge and machine them oil pans instead of more costly cast In order for pan and cover gaskets flat if any warpage is found. As with aluminum. to seal properly the surfaces must be the head/block seam, premium gaskets Older style cork/rubber gaskets clean, dry and as flat as possible, free of graphite or with synthetic faces and don’t last forever and have a tendency from anything that might catch or tear perhaps a printed-on bead are com- to leak, which is why most of these the gasket material. The surface must monly available, and usually no gaskets are no longer used by OEMs. also be free of any old gasket residue. retorquing is needed. Most manufacturers use molded rub- Oil pan sealing innovations include Another relatively new type of ber or plastic carrier gaskets for these metal grommets in the boltholes or manifold gasket has a metal or plastic applications.The plastic carrier gasket shouldered fasteners to guard against carrier with rubber inserts or deposit- is much more durable and can last as over-torquing, and one-piece rubber ed rubber beads.You have to try pret- long as the engine without failure. gaskets. ty hard to make a mistake while Over-tightening these gaskets will For timing chain covers, thermostat installing these gaskets because the often crush or crack the gasket, which housings, etc, a thin paper-type gasket carrier acts as a positive stop so the then leads to a failure down the road. is often used with a thin bead of a rubber cannot be over compressed. Some pan and cover gaskets have good sealant. Like all other parts of the These gaskets don’t require any sealant extra features that allow them to be engine, careful torquing procedures either. installed more easily than standard are required with these gaskets. PPMG Also, V8 and V6 engines that have cork/rubber gaskets. Features include tabs or endstrips on the manifold gaskets should be handled carefully. The tabs are easy to dislodge while you’re lowering the manifold into place.You can use a light coat of adhesive if you want to try and keep them in place. Intake manifold bolts should be tightened in a pattern similar to the sequence used to torque the cylinder head down. The goal here is to work from the center outward unless manufacturer specifications say otherwise. Do not over-torque these bolts. Not only will this save you from the disas- ter of a snapped bolt, but on some applications it can prevent a head gasket failure. The pressure from the weight of the manifold can push the heads outward enough to reduce clamping force that could lead to a blown head gasket. Valve Cover and Pan Gaskets The most basic type of gasket is the cut gasket, which are made by die- cutting sheets of fiber-reinforced paper-like material or ground cork/rubber to create the flange shape of the cover. Cut gaskets are most often used in timing covers, valve covers, oil pans, intake manifolds, carbure- tors, throttle bodies, water pumps, Circle 105 for more information www.enginebuildermag.com | PERFORMANCE PARTS & MACHINING TECH GUIDE 5 6-9 Bores/rings 4/15/09 10:53 AM Page 6

rying to classify the engines are now built with 0.6 mm spray coatings. American performance rings. These skinny rings produce very Another reason for the smaller rings market into a single niche is little tangential load (about 1.5 pounds), in many performance engines is that T an exercise in futility.Simply which minimizes friction and allows pistons are getting shorter. Longer con- saying “performance is alive the rings to conform more easily to necting rods with shorter pistons and well” can be proved by looking at any bore distortion. Many of these change the combustion dynamics and the scope of the performance piston engines are also using Napier-style provide better angularity during the market. second rings, with a small notch in the power stroke. Shorter pistons also weigh Cubic inches is the name of the game bottom face of the ring to improve oil less, which means the engine can rev today.The performance piston market is control and sealing as the ring scrapes higher. But when the piston is shorter, being driven by bigger bore blocks and against the cylinder wall. The napier the rings have to move up higher.This stroker crankshafts.Top rings are running design is also used with a positive twist means they have to be narrower, hotter than ever before, thanks to higher to improve its sealing characteristics, stronger and more heat resistant because combustion temperatures and piston effectively helping to prevent detona- the top ring is closer to the combustion loads combined with rings that are relo- tion by keeping oil out of the combus- chamber. cated closer to the top of the piston for tion chamber. So what does this mean inside an longer stroke crankshafts. Even at the Sportsman racing level, engine? It means ductile iron and steel With the performance piston market advancements in ring technology have rings can survive in racing environ- being driven by a wider range of vari- been seen.While cast iron piston rings ments that may be too demanding for ables than ever, piston ring suppliers remain popular with many budget- grey cast iron rings. Stronger rings have had to work hard to keep up as minded dirt track claimer motors as reduce the risk of ring breakage under well. Most performance pistons have well as many street performance and severe loads. Steel rings also show less some type of coating or anodizing other racing applications, ductile iron side wear and ring groove pound out. treatment in the top ring groove to pre- or steel rings are usually required for vent the ring from welding itself to the higher output engines. Ductile iron Bore Finish piston or pounding out in the groove. rings have roughly twice the tensile Regardless of what kind of rings or lin- The top ring,in most cases,must also be strength of gray cast iron, and three ers are used in a performance motor, steel or ductile iron, and faced or coat- times the fatigue strength. Steel rings, rings usually work best when the cylin- ed with some type of wear-resistant by comparison, have almost four times der bores are given a plateau finish. A material such as moly,chrome, nitriding the tensile strength and fatigue plateau finish essentially duplicates a or one of the new “aerospace” vapor strength of gray cast iron. “broken-in” bore finish, so there is less disposition or plasma spray coatings. For high boost turbocharged and scrubbing and wear on the rings when Moly is still the most popular facing supercharged engines, and engines the engine is assembled.What’s more, if material for many piston rings because using large doses of nitrous oxide to add the surface is finished correctly it will of its excellent wear and scuff resist- horsepower, ductile iron or steel top provide plenty of flat, smooth bearing ance.Another material is tungsten car- rings are probably a must. Many racers surfaces to support the rings while also bide (for hard liners), and chrome. prefer to use nitrided rings made from retaining oil in the crosshatch valleys to Chrome-faced rings are still a good steel wire because the rings can handle lubricate the rings. choice for abrasive environments like high loads and thermal shock better The only exception to this is in dirt tracks, and work best with cast than other materials. Nitriding pene- motors where there is a lot of bore dis- iron blocks and cylinder liners. trates into the metal and won’t flake off tortion. If the bores go out of round Chrome rings don’t work well with like other surface coatings. when the head bolts are torqued down, chrome plated bores or hard faced Most performance pistons have the rings may not seat as well allowing cylinder bore liners such as those coat- some type of coating or anodizing increased blowby and oil consumption. ed with nickel/carbide coatings. treatment in the top ring groove to pre- Thinner rings that can conform to the Thin is in, both at the beach and on vent the ring from welding itself to the bore will work better in these kinds of the track. Thinner rings generate less piston or pounding out the groove. applications, but it’s also a good idea to tension and reduce friction, so ring The top ring, in most cases, must also use torque plates when honing when dimensions have been shrinking in be steel or ductile iron, and faced or honing the bores to simulate the distor- many racing engines. Many top level coated with some type of wear-resist- tion that occurs when the cylinder drag racing and stock car engine ant material such as moly, chrome, heads are installed.The other option is builders go with compression rings as nitriding, or one of the new “aero- to go with a slightly rougher “peaked” thin as 0.7 mm, and most Formula One space” vapor disposition or plasma finish to seat the rings.

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Most ring manufacturers recom- #400 vitrified stones, and finish with ed abrasive balls that are mounted on mend using a two- or three-step hon- #600 stones, cork stones, a plateau hon- flexible metal shafts so the balls can eas- ing procedure to achieve a plateau fin- ing tool or brush. ily conform to the surface. Brushing ish. First, rough hone to within .003˝ of If the cylinders are rough honed helps sweep away torn and folded metal final bore size to leave enough undis- with diamond, they can be finish honed on the surface while removing many of turbed metal for finish honing. For with a finer grit diamond, a fine-grit the sharp peaks to make the surface plain cast iron or chrome rings in a vitrified abrasive or a plateau honing smoother. stock, street performance or dirt track tool or brush. Because diamond is a When finishing the cylinders with a motor, hone with #220 grit silicon car- harder material and wears more slowly brush, only light pressure is required. bide stones (or #280 to #400 diamond than conventional abrasives, it cuts dif- The rpm of the brush should be similar stones) to within .0005˝ of final size. ferently and may require more honing to that which the cylinder was original- Then finish the bores with a few strokes pressure. But many newer diamond ly honed, and no more than 16 to 18 using an abrasive nylon bristle plateau stones now use a more friable bond that strokes should be applied (some say 8 to honing tool, cork stones or a flexible stays sharp and doesn’t load up, allowing 10 strokes is about right). Too many abrasive brush. the stones to cut smoother and leave a strokes with a brush may produce too For moly faced rings in a street per- rounder, smoother bore finish. smooth a finish in a cast iron cylinder formance, drag or circle track motor, When using diamond-honing stones that won’t retain oil. Reversing the hone with a conventional #280 grit sil- instead of vitrified abrasives, you gener- direction of rotation while brushing icon carbide vitrified abrasive, then fin- ally have to use a higher number grit to helps to remove the unwanted material ish by briefly honing to final size with a achieve the same Ra (roughness aver- on the surface.The end result should be #400 grit vitrified stone or #600 grit age) surface finish.The actual numbers a cylinder that provides immediate ring diamond stone (or higher), plateau will vary somewhat depending on the seal with little if any wear on the cylin- honing tool, cork stones or a brush. brand and grade of the stones. der wall or rings when the engine is For stock and street performance Bristle style soft hones (plateau hon- first started. engines with moly rings, an average ing tools) have mono-filament strands With the right plateau honing tech- surface finish of 15 to 20 Ra is typical- that are extrude molded with a fine niques, you should be able to get the ly recommended. For higher classes of abrasive material embedded in the surface down to an average roughness racing, you can go a little smoother, strands. The filaments are mounted in of 8 to 12 Ra or less, with Rpk (relative provided you don’t glaze the cylinders. different types of holders for use with peak height) numbers in the 5 to 15 For moly or nitrided rings in a per- portable or automatic honing equip- range, and Rvk (relative valley depth) formance motor, hone with #320 or ment.Another type of brush uses mold- numbers in the 15 to 30 range. These numbers are meaningless unless you have a surface profilometer that can ADVERTISER measure them (which a growing num- Information Center ber of performance shops now have). ADVERTISER PAGE # CIRCLE # Crosshatch Crosshatch is also important because the COMP PERFORMANCE GROUP 9, 17 109, 117 amount, depth and angle of the crosshatch in the cylinder bores determines DIAMOND PISTONS COVER 3 121 how much lubrication the rings receive and the rate of ring rotation. Excessive shallow crosshatch angles DURA-BOND 2,13 102,113 can hinder or slow down the necessary ring rotation that allows the rings to dis- ENGINE & PERFORMANCE 15, COVER 4 115, 122 sipate heat. It can also leave too much oil WAREHOUSE on the cylinder wall allowing the rings to skate over the surface and the engine to use oil. Too steep of a crosshatch angle HASTINGS 4, 7 104, 107 may not provide enough oil retention and can result in dry starts and premature MAHLE CLEVITE 3, 5, 10, 11, 19 103,105, 110,111,119 ring wear. A steep crosshatch angle can also create excessive ring rotation that MR. GASKET COVER 2,14 101,114 accelerates ring and piston groove wear.

8 PERFORMANCE PARTS & MACHINING TECH GUIDE | April 2009 6-9 Bores/rings 4/15/09 10:53 AM Page 9

Ring manufacturers typically rec- .026˝ with a four-inch bore). the back wall of the ring groove. Gas ommend a crosshatch angle of 22° to The recommended end gaps for sec- ports work best at high rpm (above 32° from horizontal and uniform in ond compression rings are also the same, 7,000 rpm) and are not recommended both directions. with slightly larger gaps if you want to for street engines. minimize pressure buildup between the Getting rid of the end gap altogether Ring End Gaps rings. can also improve sealing, cooling and Tradition said the end gaps on second The recommended ring end gap for horsepower. Gapless rings eliminate the compression rings could be tighter most oil rings (except the new super gap between the ends of the ring by because the number two ring is not narrow one-piece rings) regardless of overlapping slightly. Gapless rings are exposed to as much heat as the top ring. engine application is typically .015˝. available in popular sizes with various Today’s theory says it’s better to open up Another trick to improve ring sealing wear-resistant face and side coatings. the second ring gap 20 to 30 percent so at high rpm is to run pistons that have Some engine builders who have pressure doesn’t build up between the gas ports behind the top ring. switched to “gapless” top or second rings and cause the top ring to lose its Combustion pressure blows through the compression rings say they’ve gained seal at high rpm. The result is better port to help seal the ring from behind three to five percent more horsepower compression, better piston cooling and and underneath. Some use vertical gas with no other changes. Gapless rings are reduced oil consumption. ports with holes drilled from the top of said to allow less than 1 cubic foot per Any pressure that builds up between the piston to the top ring groove just minute (CFM) of blowby and on alco- the rings will blow down into the behind the ring. Others use lateral gas hol-fueled engines, a gapless top ring or crankcase, keeping oil out from between ports that are drilled through the bot- second ring helps keep alcohol out of the rings. This trick works best on tom side of the top land and extend to the crankcase. PPMG engines that are running a dry oil sump and pull a vacuum in the crankcase. Some performance pistons also have “accumulator grooves” machined into the piston land between the first and second ring grooves. The added space traps blowby gasses and helps prevent the top ring from unseating and flutter- ing. For naturally aspirated engines, a top ring end gap of .004˝ per inch of bore diameter is often recommended for a stock or moderate performance engine. For a 4-inch bore, that translates into a top ring end gap of .016˝to .018˝. But this will vary depending on the power output of the engine. For drag or oval track racing, the recommended end gap is somewhat larger (.0045˝ per inch of bore diameter).With four-inch bores, that would be an end gap of .018˝ to .020˝. For a nitrous oxide street performance engine, the recommended end gap is .005˝ per inch of bore diameter (.020˝ to .022˝ for an engine with four-inch bores). For a nitrous oxide drag engine, the recommended end gap for the top ring is .007˝ per inch of bore diameter (.028˝ to .030˝ with four-inch bores). With a turbocharged or supercharged racing engine,the top ring gap should be .006˝ per inch of bore diameter (.024˝ to

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ngine cooling doesn’t only the head used in the seat area will be replacing OEM valve seats with ones happen at at the radiator. too shallow to allow a second grinding. that are of a similar material – except in The valves (particularly the If the valve seat insert shows evi- cases where extra durability is required E exhaust valves) take a lot of dence of being loose or doesn’t have because of a change in fuels (converting heat from the combustion chamber adequate interference; if there is evi- to propane or natural gas, for example), and the valve seats have the responsibil- dence of corrosion on the cylinder or an engine is being built for racing. ity of helping to cool them off. The head around the outside diameter of There are a number of different seats draw heat away from the valves the valve seat; or if there is evidence valve seat materials from which engine and conduct it into the cylinder head, that the seat has any cracking, burning, builders can choose. Many of these providing most of the cooling that the pitting or fissures, the seats must be materials will work in a wide variety of valves receive. replaced. performance applications while others Anything that interferes with the The seat alloy and hardness must are designed primarily for special appli- seat’s ability to cool the valves (such as also be matched to the type of fuel used cations such as industrial engines that a loose fit or deposits between the seat and the engine application and com- run dry fuels like propane or natural and its counterbore) can lead to prema- patible with the type of valves that are gas.The only consensus is that different ture valve failure and expensive come- installed in the engine.Again, there are valve seat materials can be used success- backs, so a cylinder head job often often differences of opinion regarding fully in most performance engines. requires valve guide and seat work to the selection and use of various seat What kind of materials are we talk- restore it for service or to improve per- materials. ing about? Everything from formance. In order for a valve to seat Nonintegral valve seats can fail for a nodular/ductile iron alloys and powder correctly, for efficiency and power, number of reasons. Most of the seats metal steel seats to hard aluminum- engine builders must replace or bring that end up being replaced are either copper and bronze alloys, and berylli- back to spec all valve seats and guides. cracked or too worn to be reground or um copper alloys. Many valve seat sup- When considering the steps neces- remachined. Seats can crack from ther- pliers have their own proprietary alloys sary to repair or replace valve seats, be mal stress (engine overheating usually), while others use industry standard aware that with two types of cylinder thermal shock (a sudden and rapid alloys. But you don’t have to be a met- heads you have three options: alu- change in operating temperature) or allurgist to appreciate the differences minum with removable valve seats or mechanical stress (detonation, excessive between some of these materials. cast iron, with removable or integral valve lash that results in severe pound- A valve seat must do several things. hardened seats. If the cast iron head has ing, etc.). It must support and seal the valve when integral seats it will need to be A small amount of valve recession the valve closes, it must cool the valve, machined to replace the seat. If the results from normal high mileage wear, and it must resist wear and recession. head is aluminum, the seat counterbore but it can also occur when unleaded Consequently,a performance valve seat may have to be machined to accept an gasoline or a “dry” fuel such as propane material should provide a certain oversize seat if the bore is loose, or natural gas is used in an engine that amount of dampening to help cushion deformed or damaged. Either way, isn’t equipped with hard seats. the valve when it closes at high rpm. you’ll need to figure the amount of Recession takes place when the seats Very hard materials, especially on the interference that is required for the get hot and microscopic welds form intake side, are not the best choice here new seat before cutting the head on a between the valve face and seat. because intake valves tend to be larger, seat-and-guide machine. Every time the valve opens, tiny heavier and close at faster rates than Valve seat replacement is required if chunks of metal are torn away and exhaust valves.The wilder the cam pro- the cylinder head was warped and blown out the exhaust. Over time, the file, the more pounding the valve and needed to be straightened before resur- seat is gradually eaten away and the seat undergo at high rpm. facing. Similarly, if an aluminum head valve slowly sinks deeper and deeper Many late model domestic and was cleaned by heating, the seats will into the head. Eventually the lash in the import engines have seats that are made need to be replaced. valvetrain closes up and prevents the of powder metal. These types of seats If the valve’s mating surface has valve from seating.This causes the valve are very hard and durable, so they typ- receded below factory specifications or to overheat and burn. Compression is ically show little wear at high mileages. if machining the head would cause the lost and the engine is diagnosed as hav- Consequently, the seats may need little seat to fall below factory specs, it must ing a “bad valve.”The seat also has to be work when the cylinder head is rebuilt. be replaced. replaced, but in many instances it may One difference between cast alloy Replace the integral seats in a cast not be recognized as the underlying seats and powder metal seats is the way iron head if the head has been ground cause of the failure. the seats are manufactured. Cast alloy before, because the hardened depth of As a rule, most experts recommend seats are made by melting and mixing

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different metals together so they com- in a molten state can be blended manufacturer can’t certify the engine. bine chemically. The molten soup is together and bonded to create totally Powder metal seats are very good at then poured into a mold and cast to unique materials. For example, in pow- handling thermal stress as well as shape. The rate of cooling and subse- der metal bushings and ball joints, impact stress, and typically show mini- quent heat treatment of the metal graphite is combined with steel to mal wear after tens of thousands of determines its microstructure, hardness, make the material “self-lubricating.” miles of use.The homogeneous consis- strength and other physical properties. Another advantage of the powder tency of a powder metal seat also Powder metal seats, by comparison, metal process is that parts can be man- improves heat transfer, which is good are made by mixing together various ufactured very close to final tolerances, for the valves, too. Powder metal seats dry metal powders such as iron, tung- reducing the amount of machining also tend to experience less micro- sten carbide, molybdenum, chromium, that’s needed to finish the part to size. welding between the seat and valve vanadium, nickel, manganese, silicon, This lowers production costs and even at high combustion temperatures, copper, etc.), pressing the mixed pow- boosts manufacturing productivity. which helps extend the life of both ders into a die, then subjecting the die The main reason why vehicle man- components. to high heat and pressure (a process ufacturers have switched from cast alloy Exhaust valves run much hotter called “sintering”). This causes the seats to powder metal seat inserts is to than intake valves so cooling is more powders to bond together and form a extend durability. Most late model critical on the exhaust side. Heat trans- solid composite matrix with very uni- engines have to be emissions-certified fer from the valve to the seat provides form and consistent properties. to 150,000 miles or higher depending cooling during the time when the One of the advantages of powder on the application and model year. If valve is closed, and by conduction up metal sintering is that materials that are the valve seats can’t go the distance through the valve stem and into the difficult or impossible to mix together during durability testing, the vehicle valve guide and head. It’s more noticeable in performance engines. Titanium valves do not shed heat as quickly as stainless steel valves, so the tradeoff for switching from steel to titanium to save weight is often hotter running valves.The higher the temperature of the exhaust valve, the greater the risk of the valve causing a preignition or detonation problem. There is also increased risk of the valve burning. That’s why many suppliers of titanium valves recommend seat materials such as beryllium copper. For racing applications using either stainless steel or titanium exhaust valves, some suppliers recommend a sintered valve seat insert, which includes a blend of finely dispersed tungsten carbide in a matrix of tem- pered M22 tool steel and special alloy iron particles.These powder metal seats have a very uniform microstructure, and are highly machinable. Because powder metal seats work harden as they age, they don’t have to be as hard ini- tially to provide good long term durability, and the self-lubricating qualities of the material allows it to handle a wide variety of fuels, including unleaded and leaded gasoline, straight alcohol, nitrous oxide and nitro methane.A shot of nitrous will cause combustion temperatures to soar, but the dose usually Circle 114 for more information 14 PERFORMANCE PARTS & MACHINING TECH GUIDE | April 2009 12-15 Valve seats 4/15/09 10:58 AM Page 15

doesn’t last long enough to have any ing to the manufacurers we surveyed, detrimental effect on the seats. run in the price range of about The next step up is a high alloy seat $18,000-$30,000, depending on the material, for applications where high options and manufacturer you choose. heat resistance is required, such as a On these machines, the cylinder head is propane or natural gas fired stationary stationary underneath a floating pow- engine but also for high performance erhead.The powerhead floats above on engines, heavy-duty and extreme duty flat ways that adjust front-to-back and engines where longevity is a must.Seats side-to-side. are made out of a high speed tungsten The powerhead weighs much less carbide tool steel, which gives it ceram- than the cylinder heads, so when you ic-like characteristics for extreme tem- center the powerhead, a procedure perature resistance. similar on most models, it floats and Conversely, because they tend to centers with the pilot. Once it is cen- run much cooler than exhaust valves, tered over the pilot, you let off the foot low alloy seats work well with intake pedal to lock it in place. This setup valves in performance applications, gives you a very rigid platform. even in such extreme cases as offshore Modern cylinder heads often have racing boats that run for hours on end. canted valves so on an older-style machine you have to tilt the fixture to Equipment Selection machine canted valve seats and guides. Seats that are cracked, loose, sunken or The fixture is relocated and set for each destroyed in some manner must be guide. When using a modern seat and replaced with new. Drilling, reaming, guide machine, the powerhead tilts, replacing valve guides, removing worn, allowing you to adjust the powerhead loose or damaged valve seats, cutting for whatever angle you need. Once new seat counterbores and machining you’ve set the powerhead angle you valve seats are all part of the recondi- can go up and down the line with the tioning process that your shop must be same tilt angle for each valve seat. Some able to handle as efficiently as possible machines can accommodate up to 15 and with precision and accuracy. degrees of rotating tilt. There are a few different kinds of Today’s valve seat and guide seat and guide machines available today machines also use three-blade carbide to fit most budgets. The first kind of cutters with three-angles or more. machine is not much more complex These cutters, or form tools, give you a than a drill press and is often referred to very consistent profile and concentric- as such. In these seat and guide ity because the profile is built into the machines the tooling sets in a solid col- tooling. Manufacturers vary with the umn and the table floats to move from type of tooling each offers, but all are guide-to-guide. These are very basic essentially a form tool with built-in seat and guide machines that have some angles. limitations compared to more The third style seat and guide advanced machines, however, there are machine is the “live pilot” design. still some small shops and hobbyists Whereas a “dead pilot” design remains that use this style of machine. A small stationary in the guide as the tooling shop may not be able to justify the larg- rotates, a live pilot spins with the tool- er, more expensive machines, and many ing in the guide.You have to be very of these small shops simply don’t have precise when fitting live pilots into the volume to be concerned about guides otherwise too much play could doing hand grinding and lapping. result in a seat that isn’t completely The second level of seat and guide round. Some live pilot machines have a machines is the floating powerhead sys- single blade carbide cutter that can tem.These machines have become the adjust while it spins to create almost an industry-standard for many engine infinite number of profiles. PPMG builders today.This equipment, accord- Circle 15 for more information www.enginebuildermag.com | PERFORMANCE PARTS & MACHINING TECH GUIDE 15 16-20 Cam bores/bearings 4/15/09 11:00 AM Page 16

hich cam is right for you? than ever to create custom camshafts what are the port runner volumes? You might as well ask for engine builders. How big are the intake and exhaust which color car is fastest. As long as an engine builder pro- valves? How about the volume of the W They’re both questions vides technically accurate specifica- combustion chambers (open chamber that can only be answered with an tions as well as detailed information or small chamber)? Are the heads alu- emphatic “it depends.” about what he expects from the minum or cast iron? Aluminum runs It depends on a variety of factors, engine, many cam suppliers will make cooler and can handle more heat with each of which is determined by a a custom cam for almost any engine. less risk of detonation.All of these fac- number of others. Sometimes the answer is an off the tors influence the lift, duration and Unless you are doing a totally stock shelf cam. Other times the right overlap that will be ground into the rebuild and reusing the original answer is a custom cam. new cam profile. camshaft, selecting a camshaft depends The variables that must be consid- • Valvetrain – What is the ratio of on what kind of engine you are build- ered include all of the following: the rocker arms? Are they stock or ing and how that engine will be used. • Engine Displacement – A smaller high-lift, and if so what is their exact A stock engine for a daily driver is displacement engine usually needs a ratio? This will affect both cam lift and obviously an entirely different applica- shorter duration camshaft for good duration at the valves. Are the rockers tion than a big stroker motor for a Pro low end torque and throttle response. steel or aluminum? How stiff are the Stock racer. So how do you navigate A large displacement stroker motor, on valve springs? Can the springs and the daunting process of selecting the the other hand, can usually handle pushrods handle the anticipated rpms? “best” camshaft for a particular engine? more cam duration without sacrificing The cam has to work with the lifters, One approach is to stick with what low end torque and throttle response. pushrods, rocker arms and valve works. If you’ve used a particular cam • Bore & Stroke – Long stroke springs to achieve the desired lift, dura- grind before that delivers good torque engines develop more torque than tion and rpm you want to achieve. and horsepower for a certain kind of short stroke motors, but short stroke • What Type of Cam and Lifters? If application, you might want to play it motors can typically rev much higher. you want a flat tappet cam, will you be safe and stick with a tried-and-true So for a high revving engine, you want using oversize lifters? Roller cams cost grind that has worked well in the past. a cam that develops power from maybe more but provide a significant reduc- But in today’s highly competitive 3,500 rpm up to 9,500 rpm. A big tion in internal engine friction, and world of professional racing, the hot stroker motor, on the other hand, may typically make more torque and horse- cam, cylinder head and valvetrain never see the high side of 6,000 rpm, power because a roller lifter can handle combination that worked well last sea- so it would need a cam that works bet- a much steeper ramp on a cam lobe son may not be the best choice for this ter at lower rpms. than a flat bottom lifter. This allows season. • Rod Length – Rod length affects roller cams to open the valves more Since technology is constantly the angularity and torque on the quickly so they can reach maximum changing with regard to cylinder crankshaft as well as piston speed, fac- lift earlier in the timing cycle. If you heads, rotating assemblies, cylinder tors that are used to optimize airflow plot valve lift and duration on a graph, head port configurations and engine in the desired rpm range. the area under the curve of a roller blocks, intake manifold manufacturers • Engine RPM Range – Are you cam with an aggressive lobe profile have had to redesign many of their building a low rpm torquer motor or a will be greater than that of a flat lifter manifold plenums and runners to flow high revving engine? The cam grinder cam for the same lift and duration more air for these stroker motors. has to know where you want maxi- specifications.This makes more power. Aftermarket engine blocks with larger mum torque to occur so he can choose • Induction System – Will the cylinder bores and bore spacing are the optimum duration, lift and lobe engine be naturally aspirated, boosted adding more and more cubic inches of separation numbers for your cam. with a supercharger or turbocharger (if displacement. • Compression Ratio – The higher so, how much boost pressure?), and/or More and more camshaft profiles the static compression ratio, the more fitted with a power adder (nitrous are required to fill the gaps not covered duration the engine can handle with- oxide)? Blown engines typically run by currently available cams.While this out going into detonation. better with slightly milder cams that can make it much more difficult for an • Cylinder Heads – Are the heads have a wider lobe separation to reduce engine builder to pick an off-the-shelf stock, modified stock or aftermarket? valve overlap. Does it have a carburetor cam that will deliver the best possible If aftermarket, which brand and model or more than one carburetor? If so, performance for a given combination of aftermarket head? Are they off-the- what’s the cfm rating of the carbure- of engine parts, gearing and usage it shelf heads or have the ports been tor(s). If the engine is fuel injected, means cam suppliers are more able reworked or CNC machined? If so, what type is it (multiport or throttle

16 PERFORMANCE PARTS & MACHINING TECH GUIDE | April 2009 Circle 117 on Reader Service Card for more information 16-20 Cam bores/bearings 4/15/09 11:00 AM Page 18

body, original equipment or aftermar- torque or high rpm power? Does he specified valve lash for mechanical ket)? How big is the throttle body? want a lumpy idle or a smooth idle? Is solid lifter cams. What kind of manifold is on the he willing to spend more for a custom Another way duration may be spec- engine (brand, split-plane or single- cam or will an off-the-shelf cam be ified is to measure it at .050˝ above the plane, low rise, high rise, tunnel ram or good enough? base circle of the cam lobe. The multi-carburetor)? Split-plane mani- You can often select cams online .050˝specs are the ones most com- folds typically produce more low end using software programs that literally monly cited in aftermarket catalogs. torque and are better for street walk you through the process. What does a duration spec tell you engines. However one of the most common about a cam? It reveals something • Firing Order – Is it stock, or are mistakes novice engine builders and about the rpm range where the cam you swapping the firing order on DIYers alike make is over-camming an will make the most power. Generally cylinders #4 and #7 on a big block or engine. speaking, the longer the duration the small block Chevy for a broader They want the cam with the biggest higher the rpm where the cam makes torque curve? Obviously, you’ll need a numbers, never mind the fact that such power. Short duration cams are good different cam if the firing order has a cam may be a poor match for the for low speed torque and throttle been changed. engine or vehicle they are sticking it response while long duration cams • Street, Street/Strip or Race Only into.A wild cam in a slightly modified hold the valves open longer for better – If the engine is being built for the engine may sound great with a loping high speed breathing and top end street, will it be emissions exempt or erratic idle. But if the engine has no power. will it have to meet emission regula- low end torque or throttle response Cams with durations in the 195 to tions? If a customer wants you to build and never reaches the rpm range 210 degree range (measured at him or her a street/strip engine, how where the cam starts to really work, .050˝cam lift) are usually considered much time will it actually be run on the engine will be a dog. best for stock unmodified engines and the strip? The customer may believe it those with computerized engine con- will be a 50/50 split, but realistically it Understanding Duration trols. Once you go beyond 210 to 220 will likely be more like 95 percent Duration is one of the factors in cam degrees of duration, intake vacuum street and 5 percent strip. That affects design that affects where the cam starts to drop. This upsets idle quality where you want the engine to develop develops peak power. Duration is how and affects the operation of computer- peak torque for everyday drivability. long the cam lobe holds a valve open ized engine control systems. • Transmission – Manual or and is specified in degrees of crankshaft Performance cams typically have Automatic? Automatics typically need rotation. The duration specification durations ranging from 220 up to 280 more low end torque, especially in a will vary depending upon how and degrees or more. The longer the dura- heavier vehicle. But this can be affect- where it is measured. tion, the choppier the idle and the ed by the stall speed of the converter. As the cam spins around and a lobe higher the cam’s power range on the A higher stall speed allows the engine begins to push its lifter up, the valve rpm scale. A cam with a duration of to rev higher before it grabs, but hurts starts to open. But if the engine has 240 degrees or higher will typically fuel economy in a street driven vehi- solid lifters, the lash in the valvetrain produce the most power from 3,500 cle. If the engine will go in front of a must first be compressed before the rpm to 7,000 rpm. manual transmission, how many gears valve starts to open. If duration is If you try to compare duration does the transmission have, and is the measured from the point where the specs between different cams, though, gear spacing wide ratio or close ratio? lifter has risen .004˝above the base cir- you don’t always get an accurate com- • Final Gearing – The final drive cle of the cam lobe to when it comes parison because duration specs don’t ratio of the differential and the size of back down to within .004˝ of base cir- tell you anything about the lobes the tires will also affect the rpm of the cle, it creates a somewhat inflated themselves. Though cams from two engine as it accelerates and cruises.The value. Some cam manufacturers refer different manufacturers may have engine’s power curve should match the to this as the “advertised duration” identical lift and duration specs, the gearing for optimum performance. because it gives the biggest numbers, lobes on one cam may be ground dif- • Exhaust System – If the engine and thus appeal to engine builders ferently from those on the other. One has headers, what is the style, diameter who subscribe to the “bigger is always cam may have more of a peak shaped and length of the headers? Does the better” philosophy of cam selection. lobe while the other has a “fatter” lobe. exhaust system have mufflers or a By comparison, the Society of A “V” shaped lobe will breathe differ- cross-over H-pipe or X-pipe? Automotive Engineers (SAE) method ently from a “U” shaped lobe because • What Does Your Customer Want? for measuring duration says it is to be it doesn’t hold the valve at its maxi- Does the customer you are building measured at .006˝ above the base circle mum opening as long. the engine for want lots of low end for hydraulic cams, and .006˝ plus the One lobe profile may also close the

18 PERFORMANCE PARTS & MACHINING TECH GUIDE | April 2009 16-20 Cam bores/bearings 4/15/09 11:00 AM Page 19

valve more softly than the other, to reduce valve bounce at ings in an engine block, there are no removable caps. The high speed.Valve float can also be a problem with lobes that only option is to enlarge the bores so new oversize cam change shape abruptly unless valve spring pressure is bearings with a larger outside diameter (OD) can be increased.The profile of the lobes on one cam may also be installed. the same on both the up and down sides of the lobe (which Reason number two for line boring a block is to restore is the norm for most stock and street performance cams) proper bore alignment - a process which is often called compared to an “asymmetrical” grind (different profiles on “align” boring (or honing if a line hone is used instead of a each side of the lobe) on the other cam. boring bar). As rigid as an engine block might seem, there The only way to really compare cam grinds, therefore, is is actually quite a bit of residual stress in most castings.As a to measure and plot lift versus rotation on a graph.This can new “green” block ages and undergoes repeated thermal be done manually with a degree wheel and dial indicator cycles, the residual stresses left over from the original cast- (which is a tedious job), or with an electronic stylus that ing process tend to distort and warp the engine.This affects plots the results on a computer. the alignment of the crankshaft and camshaft bores as well as cylinders. Overlap and Separation Eventually things settle down and the block becomes Another spec you need to look at when selecting a cam is more or less stable (a “seasoned”block).The bearings as well the relative timing of the intake and exhaust valves.This can as the crankshaft and camshaft journals gradually develop be expressed either as “valve overlap” (the time during wear patterns that compensate for the distortion that has which both the intake and exhaust valves are both open) or taken place. “lobe separation” (the number of degrees or angle between Additional warpage can occur if the engine is subjected the centerlines of the intake and exhaust lobes). Decreasing to extreme stress (like racing) or overheats. If the original the lobe separation increases overlap, while increasing the crankshaft or camshaft is then replaced without align bor- separation decreases overlap. Most stock replacement cams with durations of less than 200 degrees will have lobe separations of 112 to 114 degrees. Higher duration cams for mid-range performance typically have 110 to 112 degrees of lobe separation.With racing cams, you’ll find lobe separations that range from 106 to 108 degrees for more valve overlap. Overlap occurs when the intake valve starts to open before the exhaust valve has finished closing. Increasing overlap can be a desirable thing in a naturally aspirated high rpm engine because the outgoing exhaust actually helps scavenge the cylinder to draw more air and fuel into the combustion chamber. But too much overlap at low rpm kills low end torque and throttle response by reducing intake vacuum excessively. It can also create idle emission problems by allowing unburned fuel to be drawn through into the exhaust. Why Bore? There are three basic reasons for line boring the main bearing and cam bearing bores in engine blocks. One is to restore worn, out-of-round or damaged bores. If an engine overheats or loses oil pressure, one or more bearings on the crankshaft or camshaft may seize and spin. The resulting damage to the bearing bore must then be repaired by either machining the hole to accept a standard sized bearing or an oversized bearing. With main bearings, a worn, out-of-round or damaged bore can be restored back to standard ID by grinding or milling the mounting surface of the main caps, bolting the caps back on the block, and then cutting the holes back to their original dimensions. In the case of worn, out-of-round or damaged cam bear- Circle 119 for more information www.enginebuildermag.com | PERFORMANCE PARTS & MACHINING TECH GUIDE 19 16-20 Cam bores/bearings 4/15/09 11:00 AM Page 20

ing the block, it may bind or cause technique works especially well on can reduce these maximum tolerances rapid bearing wear. Likewise, if you’re large, heavy blocks that may be too by half or more. building a high performance engine long for most boring bars. Another dimension to look at is with close tolerances, you don’t want bore wear. Bore diameters should usu- any misalignment in the main bores or OHC Applications ally be within .001˝ of specifications to cam bores. When overhead cam cylinder heads support the bearings properly, with no The third reason for line boring or came into widespread use, it quickly more than .001˝ out-of-roundness if honing a block is to correct or change became apparent that line boring or the horizontal dimension is greater bore centers or bore alignment (as honing would be needed to correct a than the vertical dimension. when “blueprinting” a high perform- variety of problems (cam bore wear, Also check for wear on the thrust ance engine).The camshaft and crank- distortion and damage as well as cylin- bearing surface of the main cap. If shaft should be parallel in the block. If der head warpage). Aluminum heads worn or damaged, this surface should they are not, line boring can correct can be easily warped by overheating. also be remachined. the misalignment to restore the proper When the head gets hot, it tends to geometry. With performance engines, swell the most in the center area. The Installation Tips there may also be a reason to change head bulges up in the middle causing For stock, street performance and the centerline of the crankshaft or misalignment in the cam bores.This, in some racing applications, a cam kit that camshaft slightly to alter the piston or turn, can cause uneven wear in the includes lifters is a good way to go. valvetrain geometry. cam bores, camshaft sticking or even Some kits also include new,stiffer valve Even though the end goal of line cam breakage. springs for higher revving applications. boring has remained constant, some If an OHC cam won’t turn in the But for professional racing, most cams innovations in the recent past have head, it means the cam is sticking are sold outright.This gives the engine made line boring anything but a bor- because either the cam is bent or the builder more flexibility in choosing ing subject. head is warped. In the case of a bent lifter configurations. One of the disadvantages of using a cam, the center cam bores will show Regardless of what kind of engine traditional horizontal boring bar is that excessive wear or be worn out of you are building, or the application it is it tends to sag.This has to be countered round. If the head is warped (which going into, always use new lifters with by using adequate support so all the many aluminum heads are), the head a new camshaft. Reusing old, worn bore holes are cut straight and true should be straightened BEFORE it is lifters can ruin a new cam. with no misalignment between holes line bored or resurfaced. Be sure to check valve-to-piston and no variations in bore size. In the past, a popular fix for OHC clearance, especially with high lift cams One way to eliminate the effects of heads with worn cam bores was to line and/or high lift rocker arms. Also, gravity on the boring bar is to use a bore the head to accept bearing shells make sure the springs do not bind with vertical boring machine. Rotating the or inserts. Nowadays, the more popular high lift cams or rockers. block and bar 90° so the block and bar fix seems to be cutting the head to Lubrication is also critical. All cam are straight up and down provides a accept a cam with oversized journals. lobes should be coated with a high truer, straighter cut says one manufac- pressure assembly lube, not just motor turer of this type of equipment. It also Alignment Checks oil (which will run off if the engine saves floor space because the machine The alignment of the crankshaft and sits for any period of time).Also, if the has a smaller footprint. camshaft bores in blocks and OHC engine has a flat tappet cam and will Another way to circumvent the heads can be checked by placing a be used for racing, special racing oil issue of bar sag is to use a 90° right straight edge in the bores or along the that contains higher levels of zinc than angle cutter attachment on a milling bore parting lines and using a feeler ordinary motor oil may be necessary machine. Instead of using a long steel gauge to check for misalignment. to prevent premature lobe and lifter bar to pass single or multiple cutters How much misalignment is too wear. through the main bores, the 90° cutter much? It depends on the engine and Camshaft break-in after the initial is lowered into the space between each the application. A light duty passenger engine start up typically requires run- main bore, then moved sideways to car engine is not as critical as a high ning the engine at 2,000 to 2,500 rpm machine the bore ID. It’s sort of like revving performance engine or a hard- for up to 30 minutes. Don’t let it idle working around a corner. working diesel engine. As a rule, most or you may wipe out a lobe. Be sure to With computer numeric controls passenger car and light truck engines check valve-to-piston clearance, espe- (CNC), each hole can be precisely call for .002˝ or less of misalignment cially with high lift cams and/or high machined to exact dimensions and the between all the bores, and .001˝ or less lift rocker arms. Also, make sure the centerline of each hole perfectly locat- misalignment between adjacent main springs do not bind with high lift cams ed and aligned with all the rest. This bores. For performance engines, you or rockers. PPMG

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