汽车构造英文Chapter 5 Cylinderblockcrankshaft and bearing service.docx
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汽车构造英文Chapter 5 Cylinderblockcrankshaft and bearing service.docx
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汽车构造英文Chapter5Cylinderblockcrankshaftandbearingservice
Chapter5
Servicingcylinderblocks
Checkingandmeasuringcylinders
Honesandhoningcylinders
Reboringcylinders
Servicingcylindersleeves
Crankshaftservice
Servicingmainbearings
Analysingbearingfailures
Technicalterms
Reviewquestions
Theengineisusuallyremovedfromthevehicleforanymajorserviceworkonthecy1inderblockandcrankshaft,althoughsomejobscanbedonewiththeengineinthevehicle.
Aswellasdismantlingandreassemblingprocedures,serviceitemsincludecheckingthecy1inderboresforwear,reconditioningthecylindersbyhoningorboring,renewingcy1indersleeves,checkingcrankshaftjournalsforwear,andcheckingandreplacingcrankshaftbearings.
Someinformationonenginereconditioningisincludedinthischapter.Whilemajoritemsareoftenhandledbyengine-reconditioningworkshops,ageneralappreciationoftheseproceduresisneededbyallautomotivetechnicians.
Servicingcylinderblocks
Afterthevariouscomponentshavebeendismantledfromthecy1inderblock,itshouldbecleanedandinspected.Theblockcanbesteam-cleaned,pressure-cleanedwithwater,orcleanedinacleaningtank.Alternatively,solventcanbeappliedbyspraygunorbrushandjettedoffwithwater.Alloldgasketsandsealingmaterialmustberemovedfromthemachinedsurfaces.
Forathoroughcleaning,theplugsthatblankoffoilpassagesshouldberemovedandthepassagesblownthroughwithcompressedair.Thepassagesmustbefreeofsludgeordepositsthatcouldhavebeenloosenedduringcleaning.
Inspection
Ageneralcheckofthecylinderblockshouldbecarriedout,asshowninFigure5.1.Checksinclude
machinedsurfaces,threadedholes,andcoreplugs.Thecylindersarecheckedforcracks,scoresandwear.
■Minutecrackswillshowupifthesuspectedareaoftheblockischeckedwithoneofthecrack–detectionmethods.
Figure5.1Checkstobemadeonacylinderblock
Machinedsurfaces
Machinedsurfacesshouldbeinspectedforburrs,nicksandscratches.Minordamagecanbecarefullyremovedwithafinefileoranoilstone.
Thetopofthecylinderblockcanbecheckedforflatnessbyusingastraightedgeandfeelergauge(Figure5.2).Thisisdoneinasimilarmannertothatpreviouslydescribedforthecylinderhead(Chapter3).Thesurfacecanbemachinedtorestoretheflatnessifnecessary,butonlyalimitedamountofmetal(forexample,0.25mm)shouldberemoved.
Figure5.2CheckingflatnessofthetopofacylinderblockwithastraightedgeandfeelergaugeMITSUBISHI
Threadedholes
ThreadedHolesinthecylinderblockshouldbeblownoutwithcompressedair.Ifnecessary,athreadcanbecarefullycleanedwithatapofthecorrectsize.Dirtyordamagedthreadscangiveafalsetorquereadingthatwillpreventcorrecttighteningofboltsduringreassembly.
Damagedorwornthreadsinthecylinderblockorothercastingscanberepairedwiththreadinserts.Thistypeofrepairismadebydrillingoutthewornthreads,tappingathreadintheholewithaspecialtap,andtheninstallingathreadinserttobringtheholebacktoitsoriginalthreadsize.Aluminiumcy1inderblocksneedspecialtreatmentbecausealuminiumhaslessstrengththancastiron.
■Formoreinformationonbo1tsandthreadsseeChapter8:
Generalengineservice.
Expansionorcoreplugs
Expansionplugsinthecylinderblockshouldbereplacediftheyshowanyevidenceofleaking.Mostplugscanberemovedbydrillingorpunchingaholeinthecentre,andthenleveringthemoutwithapunchorsmallprybar.
Toinstallanewplug,scrapeanyrustfromtherecessintheblock,coattherecesswithasuitablesealingcompoundandplacethenewplugintherecess,convexsideout.Tapthecentreoftheplugtomakesureitisseated,thenuseaflat-endedpunchandahammertodriveagainstthecentreoftheplugandexpanditintotherecess.
Cup-shapedplugaretreatedinasimilarway,exceptthatitisnotnecessarytoexpandthemaftertheyhavebeentappedintotherecessinthecylinderblock.
Checkingandmeasuringcylinders
Thecylindersdonotwearuniformly,butweartaperedandout-of-round.Theymustbemeasuredaccuratelytofindtheamountofwearandtodeterminewhatreconditioningisneeded.
Ifthewearisnotexcessive,newpistonringsandbearingscanbefittedandthiswillprovidea
satisfactoryrepair.However,ifthecylindershavewornbeyondacertainlimit,newringswillnotbesufficientandthecylinderswillhavetobereconditioned.
Measuringcylinders
Aninsidemicrometercanbeusedtomeasurethesizeofacylinder,butthemostaccuratewayofdeterminingweariswithacylinder-boregauge(Figure5.3).Thisconsistsofadialgaugewithaguidetolocateitinthecylinder.Asthegaugeismovedupanddownthecylinder,thepointerofthegaugewillshowanyvariationsinthesizeofthebore.
Figure5.3Cylinder-boregaugeusedtocheckcylinderwear
Cylindersaremeasuredinthefollowingway:
l.Beforemeasuringcylinderwear,wipethecylindercleanandexamineitforscoresandvisiblewear.
2.Placethecylinder-boregaugeacrossthecylinder,justbelowtheunwornringridge.
3.Turnthebezeltosetthedialgaugetozero.
4.Movethegaugeslowlyupanddownthecylindertomeasuretaper.Thepointerwillmoveonthescale.
5.Turnthecylinder-boregauge90°inthecylindertomeasureout-of-round.
Measurements
Figure5.4showswherethecylinderischecked.ReadingsshouldbetakenatA-AandalsoatB-B.
Theyshouldbetakenatboththetopandbottomofthecylinder.Thesemeasurementswillallowthewearofthecylindertobedeterminedasfollows:
Out-of-round=differencebetweenA-AandB-B
Taper=differencebetweenA-AmeasuredatthetopofthecylinderandA-Ameasuredatthebottomofthecylinder
■Thetaperischeckedat.A-Abecausethisisthethrustpartofthecylinder:
ItwillhavemorewearthanB-B.
Figure5.4Cylinder-boremeasurements
A-Ameasurementatrightanglestothecenterlineoftheengine,B-Bmeasurementparalleltothecenterlineoftheengine
Conditionofcylinders
ThepartsofacylinderthatnormallywearareshowninFigure5.5.Weariscausedbythepistonringsrubbingonthecylinderwalls.Verylittlewearisactuallycausedbythepiston.Ringwearleavesridgesinthecylinderalthetopandbottomlimitsofringtravel.
Figure5.5Cylinder-borewearandgauge-wearareasareshownexaggerated
■Thepistonringsnaturallyexpandagainstthecylinderwall,buttheyarealsoforcedoutwardbygaspressure.
Thetypesofwearthatcanbefoundinthecylinderswhenanengineisdismantledareboredistortion,waviness,scuffingandscoring(Figure5.6).Theseconditionsaredescribedinthefollowingparagraphs.
Thetopofthecylindersuffersthegreatestwear,andthisleavesadefiniteringridgeinaworncylinder.Thelowerringridgeisnotasnoticeablebecauselesswearoccursatthebottomofacy1inder.Thebottomofthecylinderbelowtheringtravelisalmostunworn.
■CylinderwearisalsoillustratedinFigure4.9inthepreviouschapter.
Boredistortion
Thiscanbecausedbyunevendistributionofcoolantaroundthecy1inders,orbyincorrecttighteningofthecy1inder-headstuds.Boredistortioncansometimesbeidentifiedbyobviousdiscolorationofthecy1inders.butthisisnotalwaysthecase.
Waviness
Thisisaseriesofparallellinesorlowridgesrunningaroundthebore.Wavinesscanbeatanypartoftheborebutismainlyfoundinthetopregionsofringtravel.Wavinessisaconditionthatishardtomeasure,butitcanbeseenandcanbefeltbylightlyrunningthefingerverticallyinthebore.
Scuffing
Thisisevidentfromsmallareasofthecy1inderwallthathavediscolorationandminuteraisedareasinwhichparticlesofthepistonringhavecold-weldedthemselvestothecylinderwalls.
Figure5.6Possiblecylinderconditionsinawornengine
Scuffingcanbetheresultoflocalizedhotspotsinthecylinderwater-jackets.Thiscouldbecausedbydepositsthatallowsmallareasofthecylinderwalltoreachhightemperatures.Itcouldalsobetheresultofcontinuedoperationoftheenginewithlossofcoolant.
Incorrecttypeorgradeofoilcouldcreateproblems.Hightemperatureswillbreakdownthelubricating-oilfilmandallowmetal-to-metalcontactbetweenthepistonringsandthecylinderwall.
Scoring
Thiscanbeanadvancedstageofscuffing,inwhichpistonringparticleshavescratchedthecylinder
surface.Brokenringsorabrasivescanalsocauseborescoring.Providedscoringisnotdeep,honingthecylindercanbeusedtocorrectit.
■Withscuffingandscoring,thepistonwillalsobesimilarlyaffected.
Honesandhoningcylinders
Cylinderswithlimitedwear,orwithanyoftheconditionspreviouslyoutlined,canusuallyberestoredbyhoning.Thisdoesnotapplytobadlywornordamagedcylinderswhichwillhavetobereconditionedbyreboringorsleeving.
Thecylindersofaluminiumcylinderblockscanberestoredbyhoningbut,forsomeengines,themanufacturersdonotrecommendreboring.
Cylindersingoodconditionarenotusuallyhonedbeforefittingnewpistonrings.Generally,thesurfaceofthecylindersissuitableforreplacementringswithoutanytreatment.However,ifthecylindersareglazed,theyareusuallygivenalighthone.
Therearetwotypesofcylinderhones.Onehasrigidstonesandtheotherhasalargenumberofsmallbeadsofabrasivearrangedintheformofabrush.Honestonesaremadeofaluminiumoxideorsiliconcarbide(碳化硅或金刚砂),bothareveryhardabrasives.,
Beforeusingahone,allexposedparts,suchasthecrankshaft,shouldbecoveredwithoil-soakedragsthatwillholddustandparticlesofab
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