Ontheonehand,thecrankpinconnectstheleftandrightcrankstogether,ontheotherhand,itconnectstheconnectingrodandthecrankshaftthroughthebigendholeoftheconnectingrod.Whentheengineisworking,theforceactingonthecrankpinisverylarge.Asthecrankpinofvarioustypesofvehicleshaslittledifferenceinmaterial,heattreatmentandmachiningaccuracyrequirements,itispossibletorepairandreplaceit.Butwhenconsideringthereplacementofcrankpin,wemustpayattentiontotwopoints:first,thestructuraldimensionofcrankpincanmeettheuserequirementsafterrepair;second,itcanmeetthelubricationrequirementsofengine. Thestructureofcrankpinisdifferentwithdifferentlubricationmethodsofcrankconnectingrodmechanism.Thereareusuallysolidpin,through-corepin,through-holepinandsoon.Theengineadoptsmixedlubricationmodels,suchasdomestic250andothermodels,whosecrankpinsaresolidpins,whichcanbereplacedbythroughpinswithsufficientstrengthduringrepair.Theengineadoptsseparatedlubrication(lubricatingoilismixedwithcombustiblemixtureincarburetor,andthenenterscrankcasetogether),suchasYamahadx100,yb100andothermodels.Thecrankpinismostlythrough-centerpin.Ontheonehand,itcanreduceweightonthebasisofsufficientstrength,ontheotherhand,itisconducivetooilmistcollusioninthecrankshaft,butifsolidpinisusedinstead,theeffectisnottoogreatObvious. Fortheenginemodelswithdirectionallubrication,suchasSuzukiA100,A50,A80,HondaCG125,CD70,etc.,thecrankpinisprovidedwithsmallholesforcirculatinglubricatingoil,soastolubricatethelargeendneedlerollerbearingofconnectingrod.Thiskindofcrankpinmustnotbereplacedbysolidpinorcrankpinwithincorrectoilholeposition. Somecrankpinscanbedirectlyusedinterchangeably,suchasthoseonYamaharx125andSuzuki125motorcycles.Ifnecessary,thecrankpinsonthesetwotypesofmotorcyclescanalsobeusedonXingfu250motorcycles,orthecrankpinsonXingfu250motorcyclescanbeusedonthesetwotypesofmotorcycles. Somecrankpinsoncarscanbeusedassubstitutesafterrepair.Forexample,thecrankpinofXingfu250motorcyclecanbeusedonYamahadx100motorcycleafterbeingshortened.IfthecrankpindiameterofYamahadx100motorcycleisprocessedfrom22mmto20mm,itcanbeusedonHondah100smotorcycle.Afterthediameterisreduced,thehardnessdoesnotdecrease.

Whataretheheattreatmentmethodsofautomobilepistonpin? First,processingroute Differentrawmaterialformscorrespondtodifferentmachiningroutes.Atpresent,therawmaterialssuitableformanufacturingpistonpinaregenerallyhot-rolledroundsteel,cold-rolledroundsteel,hot-rolledseamlesssteelpipe,cold-rolledseamlesssteelpipe,etc.Therefore,accordingtodifferentrawmaterialpistonpinproduction,thefollowingdifferentprocessingroutescanbemade:1)hot-rolledroundsteel→roughturningoutercircle→drillinginnerhole→carburizing→Quenchingandtempering→grinding→finishedproduct;2)coldrollingroundsteel→drillinginnerhole→carburizing→quenchingandtempering→grinding→finishedproduct;3)hotrollingseamlesssteelpipe→roughturningoutercircle→carburizing→quenchingandtempering→grinding→finishedproduct;4)colddrawingseamlesssteelpipe→blanking→carburizing,quenchingandtempering→grinding→finishedproduct. Second,qualitycontrolofcarburizedlayerofpistonpin(20Cr) Thequalityofcarburizedlayerismainlycontrolledbythesizeofcarbides.Generallyspeaking,thesurfaceofchromiumcontainingsteeliseasytoformmassivecarbideswhencarburizing.Theformationconditiondependsonthecarboncontentofcarburizedlayersurface,whichcanalsobesaidtobethecarbonconcentrationduringcarburizing,regardlessofthecoolingmodeaftercarburizing.Thiscarbidecannotbeeliminatedevenifitisdirectlyquenchedaftercarburizing,soitcannotbeeliminatedbynormalizingaftercarburizing.Thiskindofmassivecarbideweakensthecombinationofcarburizedlayerandmatrixstructure,andalsoeasilycausesstressconcentrationandmakescarburizedlayerbrittle.Sothewaytosolvethisproblem:first,limitthecarbideintherangeofgrindingamount,increasegrindingallowance,soastoremoveitinthesubsequentgrindingprocess.Secondly,thecarburizingpotentialiscontrolledbyamicrocomputercontrolledatmospherecarburizingfurnace.Themaximumcarburizingpotentialoffurnacegasis1.25%,themaximumsurfacecarbonpotentialis1.15%,thefinalsurfacecarbonconcentrationis0.85%,andthediffusioncoefficientis1.60.Atthesametime,thecarburizingtimeisshortened,thediffusiontimeisprolonged,andthecarbonconcentrationinthesurfacelayerisdecreased,whichcaneffectivelycontrolandreducethedepthofmassivecarbide.SeeFig.1forcarburizingprocessofpistonpinwithcarburizingdepthof1.2mm. Third,twotimesquenchingprocessofpistonpin(20Cr) Theimprovementofthequalityandservicelifeofautomobilepistonpindependsonthereasonableheattreatmentprocess.Theheattreatmentprocessofpistonpinismainlycarburizingandquenchingprocess.Carburizingsteel(20Cr)isgenerallyquenchedandtemperedatlowtemperatureaftercarburizing.However,forthepistonpinwithhighperformancerequirements,theheattreatmentprocessoftwicequenchingandtemperingcanbeadopted.Becausethepistonpiniscarburizedunderhightemperatureforalongtime,thegrainsizeissignificantlycoarsened,andthesurfacelayeriseasytoformanetworkcementite.Suchabadstructurewillreducethestrengthofthepistonpin,reducethewearresistanceandincreasethebrittleness,especiallytheimpacttoughness.TherearetwowaystoeliminateitSecondaryquenching.ThefirsttimethequenchedpartsareheatedtoaboveAC3,three-phaserecrystallizationoccursabovethistemperature,thecoreisrefinedaftercooling,andthesurfacenetworkcementitedissolvedinausteniteiseliminated,soastoimprovethecorestrengthofpistonpin.ThesecondtimequenchedpartsareheatedtoacertaintemperatureaboveACCM.Duetothefirsttimeheating,thecorestructureisfullyaustenitizedtoavoidtheappearanceofundissolvedferrite.However,thehighcarbonpartofthesurfaceinevitablytendstooverheatandthestructureisrelativelycoarse.Inordertoimprovethesurfacestructure,thesecondtimeofheatingquenchingforhypereutectoidsteelisconducted.Thesecondtimeofheatingislowerthantheprevioustemperature,sothesurfacestructureisnotAsforthecorestructure,thesecondheatingistoreheatinthequenchedmartensitestate,refinethecarburizedlayerstructure,improvethesurfacehardnessofthepistonpin,andenhancethesurfacewearresistance.Aftercarburizingandquenching,thepistonpinwithhighcontentofalloyelementsshouldbecooledtoreducetheamountofretainedausteniteinthecarburizedlayerandimprovetheuniformityandstabilityofthesurfacehardnessofthepistonpin.SeeFig.2fortwicequenchingandtemperingprocess. Fourth,theinfluenceofcarburizationofpistonpininnerholeonfatiguelife Accordingtothetestresultsofphotoelasticstressanalysis,asshowninFigure3,thereisalargeplanetensilestressbetweenpointCandpointDintheinnerholeofpistonpin.Inmanycases,inordertoimprovethebendingandcontactfatiguestrengthoftheparts,thesurfaceofthepartsoftenproducesresidualcompressivestressthroughcarburizingandquenchingandlowtemperaturetempering.Therefore,forthepistonpinwhichisnotcarburizedandhardenedontheinnerholesurface,becausethereisnoresidualcompressivestressontheinnerholesurfaceofthepistonpin,thepointbetweenpointCandpointDoftheinnerholewillbepronetofatiguedamageatfirst,makingthepartsinvalid.However,forthepistonpinwithcarburizedandhardenedinnerholesurface,theresidualcompressivestressontheinnersurfaceofthepistonpinreducesthepossibilityoffatiguecrackontheinnerholesurface,andthefatiguecrackofthepartsusuallyoccursontheoutersurfacefirst,sothecarburizedandhardene

Ifthecrankshaftofthemotorcycleisbroken,theassemblycanonlybereplaced,becauseevenifyourepairit,theuseeffectisnotideal. Thecrankshaftassemblyofmotorcyclemainlyconsistsofconnectingrod,needlerollerbearingandcurvedcake.Thedamageofmotorcyclecrankshaftismainlyduetothedeformationofconnectingrodorthefractureofneedleroller.Nomatterwhichoftheabovetwopartsisdamaged,thepartscanbereplaced,buttheeffectafterreplacementisnotverygood,becauseyoucannotbesurethattheswingamplitudeofleftandrightcurvedcakeswillbethesame,soreplacingtheassemblyisthebestdimensionofsuchfailureRepairmethod. Asfortheinstallationprocessofcrankshaft,itisnoteasytosay,becausetheengineneedstobedisassembledcompletely,otherwisethecrankshaftcannotbereplaced,butsomepartsinsidetheenginecannotmove,suchasthegearboxgear,thestartingmechanismcannotmoveit,butitmustbecarefulwhenreplacinganyway.Therefore,theownerofthecarisbetternottodisassemblebyhimself,anditisbettertofindaprofessionalmaintenancepersonnelformaintenancesoasnottodamageotherparts.