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Camshaft LocationsCamshaft Locations

1) Cam-in-block: 1) Cam-in-block: • dated technology (but still widely used)dated technology (but still widely used)• more moving partsmore moving parts• valve movement is less precisevalve movement is less precise• can be noisier due to more moving partscan be noisier due to more moving parts

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Camshaft LocationsCamshaft Locations

2) Overhead Camshaft:2) Overhead Camshaft:• OHC, SOHC, DOHCOHC, SOHC, DOHC• more precise valve actionmore precise valve action• has replaced cam-in-blockhas replaced cam-in-block

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Variable Valve TimingVariable Valve Timing• to to enhance breathing over a wider rpm rangeenhance breathing over a wider rpm range, and thereby increase , and thereby increase

torque, manufacturers may design engines with either a,b,c or a torque, manufacturers may design engines with either a,b,c or a combination of a,b,c…combination of a,b,c… a) variable valve a) variable valve opening timingopening timing

when the valve openswhen the valve opens

b) variable valve b) variable valve liftlift how much it openshow much it opens

c) variable valve c) variable valve opening durationopening duration how long the valve is held openhow long the valve is held open

BMW

Honda

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Variable Valve TimingVariable Valve Timing

Fig. a

Fig. b

Fig. c

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Engine Block & Cylinder Head MaterialsEngine Block & Cylinder Head Materials

• materials used in engine blocks and cylinder heads construction are…materials used in engine blocks and cylinder heads construction are…

• Cast ironCast iron heavy heavy inexpensive inexpensive paintedpainted

• AluminumAluminum lighter than cast iron lighter than cast iron $$$ $$$ unpainted unpainted warps more readily when overheatedwarps more readily when overheated

• Magnesium has recently been used as well (BMW)Magnesium has recently been used as well (BMW) lighter than aluminumlighter than aluminum

• engines can beengines can be all cast ironall cast iron all aluminum or…all aluminum or… cast iron block & aluminum head (fig. a)cast iron block & aluminum head (fig. a)

fig. a

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Exhaust SmokeExhaust Smoke• blue smokeblue smoke: oil entering the combustion chamber & burning along with : oil entering the combustion chamber & burning along with

air-fuel mixtureair-fuel mixture worn valve seals and or worn valve guidesworn valve seals and or worn valve guides

usually noticeable on initial start-upusually noticeable on initial start-up noticeable on standard transmission equipped vehicles when noticeable on standard transmission equipped vehicles when

changing gearschanging gears worn oil control rings and, or cylinder wallsworn oil control rings and, or cylinder walls

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Exhaust SmokeExhaust Smoke

• white smoke white smoke (excessive amounts): coolant entering combustion (excessive amounts): coolant entering combustion chamber & burningchamber & burning ““blown” cylinder head gasketblown” cylinder head gasket

usually the result of an overheated engineusually the result of an overheated engine crack in cylinder head or possibly engine blockcrack in cylinder head or possibly engine block

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Exhaust SmokeExhaust Smoke• if cracks are suspected, head and/or block will have to be checkedif cracks are suspected, head and/or block will have to be checked

aluminum: checked with a dye (fig. c)aluminum: checked with a dye (fig. c) cast iron: magnafluxing makes cracks visiblecast iron: magnafluxing makes cracks visible pressure testing will produce bubbles from the cracks (fig. a)pressure testing will produce bubbles from the cracks (fig. a)

• cylinder heads should always be checked for warpage with a machinist’s cylinder heads should always be checked for warpage with a machinist’s straight edge & feeler gauge (fig. b)straight edge & feeler gauge (fig. b) excessive warpage will require the surface to be machinedexcessive warpage will require the surface to be machined

Fig. a

Fig. b

Fig. c

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NoisesNoises

• ticking sound: valve train noiseticking sound: valve train noise solid lifters: adjust valves (fig. a)solid lifters: adjust valves (fig. a)

require adjustment at each tune-uprequire adjustment at each tune-up similar to small enginessimilar to small engines

hydraulic lifters: replace (figs. b & c)hydraulic lifters: replace (figs. b & c)

1. quieter1. quieter

2. able to adjust for thermal expansion of the engine2. able to adjust for thermal expansion of the engine

3. built in shock absorber, eases stress on valve train3. built in shock absorber, eases stress on valve train

4. should not require periodic adjustment4. should not require periodic adjustment

Fig. a

Fig. b

Fig. c

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NoisesNoises• deep metallic knocking sound can be the result of…deep metallic knocking sound can be the result of…

worn crankshaft main bearingsworn crankshaft main bearings worn connecting rod bearingsworn connecting rod bearings low oil pressurelow oil pressure

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Poor PerformancePoor Performance• low compressionlow compression

valve and seat problemsvalve and seat problems cylinder & compression ring wearcylinder & compression ring wear

ridge reamer needed before piston can be removedridge reamer needed before piston can be removed

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Poor PerformancePoor Performance• can also be caused by…can also be caused by…

camshaft drives that are out of timecamshaft drives that are out of time usually caused by worn components that have “jumped a tooth”usually caused by worn components that have “jumped a tooth”

Remember: cam and crank MUST be timed on all engines!!!Remember: cam and crank MUST be timed on all engines!!!

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Leaks - OilLeaks - Oil

• always investigate oil leaks “top down”always investigate oil leaks “top down” valve cover(s) (a)valve cover(s) (a)

students can confuse this for head gasketstudents can confuse this for head gasket cylinder head gasket (b)cylinder head gasket (b) oil pan gasket (c)oil pan gasket (c) front crankshaft sealfront crankshaft seal rear crankshaft seal (d)rear crankshaft seal (d)

• steam clean the engine firststeam clean the engine first• test PCV system – valve, hose etc.test PCV system – valve, hose etc.

if it’s not working, pressure will build in engine & cause leaksif it’s not working, pressure will build in engine & cause leaks

a

b c

d

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Valve ServiceValve Service

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Hey Roger, can your students fix it for me?Hey Roger, can your students fix it for me?• Minor/doable (depending on the vehicle) repairs…Minor/doable (depending on the vehicle) repairs…

cylinder head gasket replacementcylinder head gasket replacement timing chain, belt, gear replacementtiming chain, belt, gear replacement engine re & re (with a used one)engine re & re (with a used one)

• Major Repairs…Major Repairs… ““low cost” rebuildlow cost” rebuild

hone cylinders & new ringshone cylinders & new rings valve grindvalve grind new camshaftnew camshaft new rings, timing belts or gears & bearingsnew rings, timing belts or gears & bearings all new seals & gasketsall new seals & gaskets

full engine overhaulfull engine overhaul bore & hone cylindersbore & hone cylinders grind & polish crankgrind & polish crank valve grindvalve grind new valve guidesnew valve guides resurface head(s)resurface head(s) new rings, timing belts or gears & bearingsnew rings, timing belts or gears & bearings all new seals & gasketsall new seals & gaskets

• Consider…Consider… how long can the vehicle be left in you shop?how long can the vehicle be left in you shop? do you have a machine shop you really trust?do you have a machine shop you really trust? how much $$$ does the owner have?how much $$$ does the owner have? tackle only what you are comfortable withtackle only what you are comfortable with good used original engines are often better than rebuilt enginesgood used original engines are often better than rebuilt engines