16Engine ComponentsC H A P T E R 2Identify the basic components of a small engine and describe the function of each component.Describe engine block variations.Describe the construction and operation of the crankshaft.Explain piston design considerations and differentiate between types of piston rings.Describe connecting rod and bearing variations.Identify common valve train configurations.

Learning ObjectivesPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.3Engine BlockKeeps engine parts in alignmentCast iron or aluminum alloyConsists of two sections:Cylinder blockCrankcasePermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.4Cylinder BlockContains cylinder boreCylinder may be bored directly in blockAluminum cylinder blocks cast around steel sleeveCylinder head bolts to block or is cast as integral partCooling fins on block and head of air-cooled enginesPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.5CrankcaseContains crankshaftMust withstand rotational forces of the crankshaftMay contain oil for lubricationMay be cast with engine blockPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.6CrankshaftMajor rotating part of engineConverts reciprocating motion into rotary motionTransmits engine torqueDrives camshaftSupports flywheelPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.7CrankshaftCast or drop forged steelTapered end receives flywheelFlywheel keyed to crankshaftCrankshaft throwOffset portion of shaft Counterweights offset unbalance

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.8Crankshaft Main BearingsSupports crankshaft in blockThree types:Sleeve or bushingRoller bearingBall bearingPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.9Crankshaft Main Bearings

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.10Crankshaft Main Bearings

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.11Crankcase SealsPrevent leakageShell makes fixed contact with crankcaseKnife edge rubs crankshaftCoil spring keeps sealing lip in contact with shaftPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.12Crankcase Seal

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.13PistonsStraight line driving memberSubjected to heat of combustionAdequate clearanceSeal between combustion chamber and crankcasePiston rings exert tension on cylinder wall

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.14Piston ConstructionSteel or aluminumAluminum most popularGrooves accept piston ringsLands are full-diameter ridges between groovesHoles in bottom groove allow oil to flow back to sumpHole for piston pin (wrist pin)Pin boss surrounds the piston pin holePiston skirt keeps piston from tipping

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.15Piston Construction

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.16Cam Ground PistonOval shapeThrust surfaces fit more closelyHelps prevent piston slap

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.17Piston HeadRuns hotter and expands more than skirtSmaller in diameter than skirtShape depends on applicationFour-stroke enginesFlatDomedWedgeTwo-strokeFlat with loop-scavenged engineRaised baffle or deflector with cross-scavenged enginePermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.18Piston RingsAllow piston to compress fuel chargePrevent burning gases from leakingRide on cylinder wallsSeparated by thin film or oilRub sides of piston groovesGrooves hold rings squarely to borePermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.19Piston RingsFour-stroke pistons use three ringsTwo upper rings are compression ringsLower ring is oil control ring

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.20Compression RingsProvide strong sealKeeps compressed air-fuel mixture and burning gases above pistonPrevents passage between piston and cylinder wallTwists in groove during intake strokeIn tipped position during compression and exhaust strokesFlat against cylinder wall on power strokePermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.21Compression Rings

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.22Remove surplus oil from cylinder wallsLight scraping actionSlotted or perforatedOil passes through holes in ring and grooveOil flows to inside of piston and into crankcase

Oil Control Rings

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.23Piston Ring ConstructionCast iron or steelPlated with long-wearing material Outside diameter slightly larger than cylinder boreCreates ring tensionRing gapOpening between ends of ring Allows rings to expand and contractPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.24Piston Ring MovementFree to move inward or outward in piston groovesFloating ringsRotate around groovesInstalled with end gaps staggeredPinned ringsHeld in position by pin in ring groovePin prevents rotation of ring around grooves

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.25Piston PinsSecure piston to connecting rodCase-hardened steelSolid or hollowFull-floating pinRetained by snap ringsPress-fit pinFits tightly in connecting rod

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.26Attaches piston to crankshaftUpper end accepts piston pinLower end contains bearings and fits around crankshaft journal

Connecting Rod

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.27Friction BearingsUsed when lower end of connecting rod is splitTypesRod metalBearing bronzeRemovable precision insertsLocating tabFits into slot in rod

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.28Antifriction BearingsRollers or balls reduce frictionElements held together by roller cage or can be freeHardened and ground to exact sizeMust fit accurately and have clearance for expansionPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.29Intake and Exhaust PortsProvide means for admitting air-fuel mixture and exhausting waste productsTwo-stroke engines Porting of cylinder wallsAlternately covered and exposed by pistonFour-stroke enginesPoppet valves open and close port openingPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.30Reed Valves and Rotary ValvesControl fuel flow directly into crankcase of two-stroke engineReed valveOpens during compression stroke and closes before the power strokeRotary valveAttached to end of crankshaftAir-fuel charge enters crankcase when holes in valve and wear plate align

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.31Reed Valve Action

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.32Rotary Valve Action(Evinrude Motors)

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.33Poppet ValvesInstalled in valve ports of four-stroke enginesControl flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinderAngled valve face closes tightly against seatValve guide aligns valve and ensures accurate raising and lowering

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.34Poppet Valves

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.35Valve SpringHolds valve firmly against seatConnect to valve stem with retainer and keeperAllows valve to be opened and closes it when pressure is released from valve stemPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.36CamshaftUsed in four-stroke enginesOpens valves the right amount at the right timeHolds valve open for a specific period and allows them to close at correct instantShaft has lobe for each valveLobe lifts valve from seat when shaft rotatesRotates at half crankshaft speedCamshaft gear meshes with and is driven by crankshaft gear

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.37Located between cam lobe and valve stemRises and falls as camshaft rotates, opening and closing valvesMay provide means to adjust clearanceValve Lifter

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.38Valve TrainTransforms crankshaft rotation into opening and closing of valvesValve train configurationsValve-in-blockOverhead valveOverhead camPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.39Camshaft located in crankcaseValves located in cylinder block, directly above camshaft lobesLifters act directly on valve stems

Valve-in-Block

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.40Camshaft installed in crankcaseValves installed in cylinder headPushrods transfer motion from valve lifters to rocker armsRocker arm pushes down on valve stemOverhead Valve (OHV)

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.41Both camshaft and valves in cylinder headCamshaft positioned directly above valves or offsetRocker arms used if camshaft is offsetCamshaft driven by chain or belt

Overhead Cam (OHC)

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.42Starter AssemblyRewind starter assemblyMounted above flywheelWhen rope is pulled, pawls engage flywheel clutch and assembly turns crankshaftWhen rope is released, pawls retract and assembly disengagesElectric starters

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.43Makes hand cranking easierLifts exhaust valve during crankingReleases part of compression pressure

Automatic Compression Release

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.44FlywheelFastened to one end of crankshaftKeeps crankshaft spinning during nonpower strokesMetal fins on flywheel force air over cylinder to cool engineContains magnets that produce electrical current for ignition system

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.45The two sections of the engine block are the cylinder block and the _____.crankcasePermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review46The _____ converts the reciprocating motion of the piston into rotary motioncrankshaft

Permission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review47The shape of a cam-ground piston allows the _____ surfaces to fit more closely.thrustPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review48The _____ rings keep the air-fuel mixture and burning gases above the piston.compressionPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review49Name the three types of friction bearings used in the big end of the connecting rod.Rod metal, bearing bronze, and removable precision insertsPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review50_____ bearings use rollers or balls to reduce friction between moving parts.AntifrictionPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review51In a(n) _____ valve train, the valves are in the cylinder block and the camshaft is in the crankcase.valve-in-blockPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review52In an overhead valve arrangement, _____ transfer motion from the valve lifters to the rocker arms.pushrodsPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review53In an overhead cam valve train, both the camshaft and the valve assemblies are installed in the _____.cylinder headPermission granted to reproduce for educational use only. Goodheart-Willcox Co., Inc.Review54