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