汽车构造英文Chapter 3 Cylinderhead and valve serviceWord文档格式.docx

汽车构造英文Chapter 3 Cylinderhead and valve serviceWord文档格式.docx

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Servicingrocker-armassemblies

Servicinghydraulicliftersandlashadjusters

Valverefacersandrefacing

Valve-seatreconditioning

Valve-seatcutters

Servicingvalveguides

Servicingvalve-seatinserts

Theconditionofthecy1inderhead,valvesandassociatedpartswillaffectenginepower,economyandperformance.

Depositsgraduallyaccumulateinthecombustionchambers,onthefacesofthevalvesandontheheadsofthepistons.Thevalvefacesandtheirseatsgraduallydeteriorateinoperationastheybecomewornandpitted.Whenthereislossofcompressionandengineperformanceisaffected,thecylinderheadneedstobeservicedtorestoreittoitsoriginalcondition.

Cylinder-headservice

Duringcylinder-headservice,thecylinderheadisremovedfromthecylinderblock,thevalvesareremovedfromthecylinderheadandallpartsarecleanedofcarbon.Thevalvesarerefacedandtheseatsgroundsothatthevalvesseatcorrectlyinthecylinderhead.

Apartfromtheproblemofagraduallossinenginepower,thecylinderheadmighthavetoberemovedbecauseofotherproblems.Theseincludeavalvethathasburnt,ablowncylinder-headgasket,oracoolantleak.Faultyvalveseatingcancausecompressioninthecylinders.Ablowncylinderbeadgasketcanalsocausecompressionlossaswellascoolantleaks.

■Themethodofcheckingcylindercompressionisoutlinedinchapter8:

Generalengineservice.

Theservicethatinvolvesremoving,reconditioningandreplacingacylinderheadisoftenreferredtoasatopoverhaul.Proceduresforremovingandreplacingcylinderheadswillvary,dependingonwhetheritisforanoverhead-valveoranoverhead-camshaftengine.Proceduresforremovingauxiliaryequipment,suchasaircleaners,air-intakesystems,,fuelsystems,exhaustsystemandemissioncontrolswillalsovaryfordifferentengines.

Whendismantlinganenginewhileitisinthevehicle,therearetwogroupsofpartstoconsider:

1.Auxiliaryequipmentandattachmentsthatareon.，orassociatedwith,theengine.

2.Actualmechanicalpartsoftheengine.

Withmostmotorvehicles,thereareanumberofpartsthathavetoberemovedbeforethemechanicalpartsoftheengineareaccessible.AnumberoftheseareshowninFigure3.1.

Theillustrationshowsacylinderheadforafourcylinder,doubleoverhead-camshaftenginewithanumberofdismantledcomponents.Someofthesearepartsthathavetoberemovedtogainaccesstothecylinderhead.Othersarepartsthataredismantledfromthecylinderheaditself.

Followingaregeneralpointsthatrelatetoremovingacylinderheadfromanenginewhileitisinthevehicle.Thesearenotprocedures-theproceduresmustbeobtainedfromtheparticularvehicle’sservicemanuals.Someservicemanualsprovidetheproceduresasdetaileddescriptions,othersprovideillustrationswithdismantlingsequencesshown.

Auxiliariesandattachments

Pointsrelatingtoauxiliarypartsandaccessoriesareasfollows:

1.Enginecover.Thecoveroverthetopoftheenginehastoberemovedtomakeotherpartsaccessible.

2.Coolant.Thecoolanthastobedrainedfromtheradiatorandalsofromtheengineblock.Unlesstheblockisdrained,coolantthatremainsintheenginewillfinditswayintothecylinderswhenthecylinderheadisremoved.

3.Coolantsystem.Coolanthoses,thethermostatandheaterhoseshavetoberemoved.

4.Air-intakesystem.Theaircleanerorductingisusuallyremovedearlyintheproceduresothatotherpartsareaccessible.

5.Acceleratorcable.TheacceleratorcableandelectricalconnectionsattheEFIthrottlebodywillhavetoberemoved.

6.Emissionpipesandhoses.Thepositionandconnectionsofemissionhosesanddevicesshouldbenoted.Labelsshouldbeattachedbeforeremovalsothatthepartscanbecorrectlyreinstalled.

7.Ignitionsystem.Thespark-plugcablesandtheignitioncoilpackswhichareattachedtotheenginewillhavetoberemoved.Ifthereisadistributor,itwillberemoved.

8.Sparkplugs.Theseareremovedsothatthecrankshaftiseasytorotate.

9.Electricalconnections.Therearevariouselectricalconnectionsintheenginecompartmentthathavetobedisconnected.Multipinconnectorscanonlybeconnectedoneway,butotherconnectionsthatarenotobviousshouldbelabelled.

10.Drivebelt.Thedrivebeltsforthealternatorandotherauxiliariesareremoved-tensionersmayhavetobereleased.

Figure3.1Componentsassociatedwithcylinderheadremovalanddismantling

1intakemanifold,2gasket,3throttlebody,4fuelrail,5fueldamper,6fuelline,7injector,8valvecover,9gasket,10shim,11buckettappet,12valvespring,13valveguide,14valve,15sparkplug,16intakecamshaft,17exhaustcamshaft,18cylinderhead,19gasket,20shield,21exhaustmanifold,22cylinder-headgasket,23timingbelt,24tensioner,25crankshaftpulley,26-28timingbeltcovers,29gasket,30camshaftpulleys,31bearingcap,32gasketTOYOTA

11.Fuelsystemparts.Manyofthesehavetoberemovedsothatotherpartsareaccessible.

Externalmechanicalparts

Thereareanumberofexternalpartsthathavetoberemoved.Theseinclude:

1.Intakemanifold.Thisisoftenintwopartswhichcanbeseparatedforremoval.

2.Exhaustmanifold.In-lineengineshaveonemanifold,whileV-typeandhorizontallyopposedengineshavetwo.

3.Valvecover.Thisisremovedtogainaccesstothevalve-operatingmechanismand,onoverheadcamshaftengines,accesstothecamshaft.

4.Enginetimingcover.Removalofoneormoretimingcoversgivesaccesstothetimingchainorbeltandtothesprocketsorpulleys.

5.Enginetiming.ThetimingmarksarecheckedandsetwithNo.1cylinderattopdead-centre（TDC）.

6.Otheritems.Wherefitted,asuperchargerwouldhavetoberemovedandpartsofaturbochargermighthavetobedisconnected.

Dismantlingthevalvemechanism

Thevalveoperatingmechanismhastoberemovedfromthetopofthecy1inderheadbeforethecy1inderheadcanberemovedfromthecy1inderblock.Thereareanumberofdifferentarrangementsandtheproceduresthatareusedwilldependlargelyonwhetheritisanoverhead-camshaft（OHC）engineoranoverheadvalve（OHV）engine.

Overhead-camshaftengines

WithOHCengines,thecamshaft（orcamshaft）areremovedfromthetopofthecylinderhead.Variationsinthedismantlingproceduresfordifferentengineswilldependon:

l.Whethertheenginehasrockerarmsorbuckettappets.

2.Whethertherearehydrauliclashadjuster.

3.Whetherthereareoneortwocamshafts.

4.Whetherthecamshafthasabeltdriveorachaindrive.

Thecamshaftsarecarriedinbearingsinthecylinderheadandareretainedbybearingcaps.Withbucket-typetappets,thecamshaftcanberemovedfromthecylinderheadandthetappetsthenremoved.Withrockerarms,thecamshaftcannotberemoveduntiltherockerarmsortherocker-armassemblyhasbeenremoved.

Somerockerarmsaremountedindividually,butmanyaremountedonbearingsorbushesonashaft.Theseareremovedfromthecylinderheadasanassembly..RockerarmsofthistypeareshowninFigure3.2.Thecamshaftbearingcapsaresecuredtothecylinderheadwithfourbolts.

Whenremovingthistypeofassembly,thebearingcapboltsarereleasedprogressivelyalittleatatime,andinasequencethatinvolvesallthebolts.Thisis

necessarybecausesomepartsofthecamshaftareunderloadfromthecompressedvalvesprings.Progressivelooseningofthebearingcapboltswillpreventdistortionoftheparts.

■Thearrangementsofoverheadcamshaftscanbeseeninanumberofthefiguresinthepreviouschapter.

Overhead-valveengines

Figure3.3showsapartlydismantledV-typeenginewithoverheadvalves.Proceduresfordismantlingthevalvemechanismincluderemovingthevalvecoverfromthetopofthecy1inderheadandtheintakemanifoldfrombetweenthebanksofcylinders.

Intheillustration,thevalvecovershavebeenremovedandthepartsofthevalvetraincanbeseen.Asinglecamshaftismountedinthecrankcaseandthisoperateshydraulicvalvelifters.Thesehaverollersthatbearagainstthecamsofthecamshaft;

therollersareusedtoreducefrictionandwear.P52

Figure3.2Valvearrangementforanin-lineOHCengineFORD

Figure3.3PartlydismantledV-8OHVengineshowingthepartsofthetrainFORD

Pushrodsarelocatedbetweenthevalveliftersandtherockerarms.Therockerarmsareindependentlymountedandtheypivotaboutafulcrumthatisretainedbyastud.Thestudisthreadedintothecylinderhead.

■ThecamshaftanddriveforthistypeofengineisshowninFigure2.27inthepreviouschapter.

Removinganddismantlingcylinderheads

Withthevalvegearremovedfromthecylinderhead,thecy1inderheaditselfcanberemovedfromthecylinderblock.Cylinder-headboltsmustbereleasedprogressivelyandinthecorrectsequence（Figure3.4）.Iftheboltsarenotallthesamelength,thelocationofthedifferentboltsshouldbenoted.

Whenarethecylinder-headboltshavebeenremoved,theheadcanbeliftedfromtheblock.Iftheheadisstuck,alevercanbeusedbetweenaprotrusionontheheadandtheblock.Donotleverbetweenthematingsurfacesasthiswillcauseburrsonthesurfacesandsealingonreassemblywillbedifficult.P53

Figure3.4Cylinderheadbolts–sequenceforlooseningandremovingTOYOTA

Dismantling,cleaningandchecking

Toremovethevalvesfromthecylinderhead,thevalvespringsarecompresse