Download - Types of Engine Bearing Damage
-
It's What's Inside ThatCounts
Search Know Your Parts
Menu
Home(http://www.knowyourparts.com)>TechnicalArticles(http://www.knowyourparts.com/technicalarticles/)>Engineand
enginemanagement(http://www.knowyourparts.com/technicalarticles/system/engine/)>TypesofEngineBearingDamage
(/)
TypesofEngineBearingDamageBroughttoyoubyAASA(/brands/)
Figure1:Overplatedcopperalloybearinggougedbycastirondebris.Insetphotoshowsthemicroscopicdetailofthegouges.
Enginebearingsbothreducefrictionbetweentherotatingpartoftheengineandthestationarypartandsupportthecrank.Thebearingmaterialmustbeextremelystrongbecauseofthestressescausedbytheexplosionsinsidetheinternalcombustionengine.Reducingfrictionisaccomplishedinpartbythefactthatdissimilarmetalsslideagainsteachotherwithlessfrictionandwearthansimilarmaterialswill.
Figure2:Babbittbearingembeddedwithmachiningdebris.Theinsetphotoshowsmicroscopicdetailofthedebris.
-
Soanalloybearingmaterialdoesamuchbetterjobofkeepingasteelcrankshaftmovingthanasteelorcastironbearingdoes.
Althoughthematerialitselfmaygivetheenginebearingsomefrictionreducingproperties,itsperformanceisenhancedbyalubricantbetweenthemovingandstationarysurfaces.Anotherofthebearingsdutiesistoestablishandmaintainafilmofoil.
Thebearingsusuallydoaverygoodjobatkeepingthemovingpartsmovinghowever,whenabearingfails,theresultscanbecatastrophic.
Figure3:Thisaluminumbearingwasdamagedbyembedmentofglassbeads.Thisphotoshowstheextentofthedamage.
Evenwhentheyfail,itsusuallynotthebearingsfault.Withabitofinvestigation,anenginespecialistortechniciancandiscoverandeliminateoneofliterallydozensofreasonsforprematurewearorfailure.
DirtorDebrisDebris,suchasdirtordust,cancausesignificantdamagetoabearingsurface.Ifitsinthelubricationsystem,dirtwillusuallyleavecircumferentialscratchesandwilloftenremainlodgedinthebearingssurface.
Figure4:Foreignparticlesinthebearingliningmaybetheresultofimpropercleaningorafailuretoreplacethefilterandmayincluderoaddirtandsand.
Besuretoalwaysflushthelubricationsystemthoroughlybeforereassemblinganenginetoavoidenginebearingdamage.
-
Anotherwaydirtcanplayhavocisiftheenginecomponentsarentcompletelyclean.Aforeignparticletrappedbetweenthebearingbackandthehousingwillcausearaisedareainthebearing.
Thislittlehumpcanleadtocontactbetweenthebearingandthecrankjournal.Youshouldalwaysensurethebearingsareinstalledincleansurfaces.
InsufficientLubricationAcompletelackoflubricationinthecrankcaseusuallyleadstoseizureofthebearingandtotalfailureoftheengine.But,expertssayamorefrequentissueregardinglubricationissimplyinadequateoiling.Theabsenceofaproperoilfilmwillresultinmetaltometalcontact,occasionallytojustonebearingoroftentoanumberofthem.
Figure5:Lubricationisvital.Thisshowstheresultofadrystart.Thebearingsontheleft,furthestfromtheoilpumphavethemostwear.
Whenthebearingisdamagedbyoilstarvation,youllfindaveryshinysurfaceandevidenceofwiping.
Remember,thefailureoftheoilfilmcanbeseeninavarietyofwaysonthebearings.Checkonsuchthingsasblockedoilpassages,amalfunctioningoilpump,improperbearingselectionorinstallation,oilsealfailures,fueldilution(oftencausedbyblowbyoffuelandairpastthepistonrings)orfoamingoraeration,caused,ironically,byanoverfilledcrankshaft.
-
MisassemblySometimes,failuresaretheresultofsimpleinstallationerrors.Forexample,ifabearinghalfwithoutanoilholeisimproperlyputintoapositionwheretheholeisneeded,thatjournalwillreceivenolubrication.
Figure6:Lowoilsupplyoroilstarvationdoesntjustsoundbad,itdoesbadthingsinsidetheengine.
Othertypesofassemblyerrorsmayalsobeseen.Ifaconnectingrodormainbearingcapisinstalledinthewrongposition,orabearingisntsetintoplacesecurely,lubricationwillbeinsufficientandcausefailure.
Carefulinstallationproceduresare,ofcourse,criticalineveryaspectofenginebuildingcarelesserrorsarealwaysexpensive.
BearingCrushThetermcrushreferstotheoutwardforcecreatedbytheportionofthebearingthatextendsabovethehousingborewhenthebearinghalvesaresetintoplace.Thisextramaterialholdstheoutsidediameterofthebearingsfirmlyagainstthehousingborewhentheassemblyistorquedtospecification.
Byincreasingthesurfacecontactbetweenthebearingandconnectingrodhousingbore,crushminimizesbearingmovement,helpstocompensateforboredistortionandaidsinheattransfer.
Figure7:Toorichamixtureorblowbypastthepistonringcanleadtodilutionoftheoil.Thisdamagecanbeseenhere.
Insimpleterms,bearingcrushiswhatholdsthebearinginplace.Thinkofitasputting10poundsofsomethingintoafivepoundbag.Thetangorlocatortabontheshellthatfitsthesaddleisonlyforlocatingthebearingduringassembly.
-
Whencrushiscorrect,slightlyellipticalbearingshellsconformtoaperfectcirclewhentheyretorquedintoplace.Inthisway,thecrankshaftrotatesproperly.
However,whenthereisexcessivecrush,theadditionalcompressiveforcecausesthebearingtobulgeinwardatthepartinglinescausingsidepinch.
Excessivecrushmaybetheresultofanattempttoreduceoilconsumptionbyfilingdownthebearingcap,assemblingthebearingcapstootightlybyovertorquingthefastenersor,insomecases,usingtoofewshims.
Insufficientcrush,ontheotherhand,willresultinbearingsthatarenotheldsecurelyinthebore,andremainfreetomovebackandforthwithinthehousing.
Figure8:Excessivewearseennearthepartinglinesofupperandlowershellswascausedbybearingcapshift.Thisresultsinmetaltometalcontactandexcessivepressurecausingdeterioration.
Becausecontactbetweenthebearingbackandhousingboreisnecessaryforcooling,thisconditionmeansheattransferawayfromthebearingisimpeded,resultinginoverheatinganddeteriorationofthebearingsurface.
Insufficientcrushmaybecausedbytheimproperattempttoachieveabetterfitbyfilingthepartingfaces,bydirtorburrsholdingthebearingcapsopen,improperlytorquingthefastenersduringinstallation,improperlysizingthehousingboreor(ifneeded)usingtoomanyshimsintheassemblyprocess.
-
Figure9:Filletrideoccursiftheradiusofthefilletinthecornerofeachcrankjournalislargerthanneeded.Theedgesofthebearingcanthenrideonthosefilletsratherthanfittingneatlybetweenthem.
OtherCluestoBearingFailureShinyareaswillbeseenonthebackofthebearingduetoitsrubbingbackandforth.Insomecases,discolorationmaybeseenwhereoilhasworkeditswaybetweenthetwosurfacesandburned.
Overloadingmaybecausedbyvehicleoperatorerror.Excessiveidlingcanresultinanoilfilmthatcantsupporttheloadneeded.
Engineluggingcandistortthecrankcaseand/orcrankshaft,affectingtheconnectingrodand/ormainbearings.
Hotrodding,orforcingexcessiveloads,cansimilarlyaffectthebearings.Enginetuningandoperatingconditionsshouldalwaysbefollowedandappropriatebearingmaterialschosenfortheapplication.
Avehiclethatleaksoilhasitsshareofissues.But,somevehicleownerswhohavecarsortrucksthatdonotleakoilareinanevenmorepotentiallyserioussituation.Atleasttheleakerletsyouknowitneedsoiladdednowandthen,withfreshoilmaintainingitslevels.
Theenginethatseemstobeleakfreecanbeoverlooked,yetafteracertainamountoftime,theoilbeginstodegrade.Theacidsintheoilthenattackthebearingsurface.
Properselectionofbearingswillgoalongwaytowardasuccessfulenginebuild.Andcheckingassembledbearingclearancestomakesurethebearingsarenottootightortoolooseshouldalwaysbedoneasafinalchecktomakesureoilclearancesarewithinthedesiredrangefortheengine.
Figure10:Whenthereisexcessivecrush,theadditionalcompressiveforcecausesthebearingtobulgeinwardatthepartinglinescausingsidepinch.
-
ContactUs(/contact/) Newsroom(/newsroom/) SiteMap(/sitemap/)
PrivacyPolicy(/privacypolicy/) Newsletter(/newsletter/)
Attentiontothemachiningandmaterialselectionprocessesatthefrontendshouldhelpreducethechanceofbearingfailuredowntheroad.Butshouldthosemysteriousbearingfailuresoccur,youshouldeasilybeabletofindthecause.
ShareThisArticle
Relatedarticles:1. EngineOil:TheRightChoiceMatters(http://www.knowyourparts.com/technical
articles/engineoil/)
2. EngineandTransmissionMounts(http://www.knowyourparts.com/technicalarticles/engineandtransmissionmounts/)
3. EngineInnovationstoReachGovernmentFuelStandards(http://www.knowyourparts.com/technicalarticles/engineinnovations/)
10Like
(http://www.ngksparkplugs.com/)(http://www.kyb.com/)(http://www.wixfilters.com/)(http://www.wellsve.com/)(http://www.goodyearep.com)
| |
| |