BMW 7系1994产水冷发电机修理.docx

BMW 7系1994产水冷发电机修理.docx

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BMW7系1994产水冷发电机修理

BMW7系（1994~2001年产）水冷发电机修理

BMWE38WATER-COOLEDALTERNATORREPAIR

Thewater-cooledalternatorsfittedtothefaceliftE38'sseemtobenon-repairableandBMWdonotsellindividualpartsforthem.Atjustshortof£800foranewalternatorand2nd-handunitshardtocomeby,thereisquiteaneedtorepairthem!

Fortunately,theycomeapartquiteeasily（aslongasyouknowhowtodoit-unfortunatelyIdidn't,butatleastnowIdo!

）,andthebearingsarereadilyavailablefromBMW.

Right,let'sgetitapart,pleasenotethatthepicturesshowpartsthatshouldhavebeenremovedbutaren't,itwasonlywhenIgotitcompletelyapartthatIrealisedhowIshouldhavedoneit.

Startbyremovingthepulleynut.Youwillneeda24mmsocketandplainwrench.Standthealternatoronawoodensurfaceandstrikethewrenchwithametalhammertoundothelargenut.Itisquitetightandmayneedafewcloutsbutitshouldcomeoffwithnoproblems.Notethereisastarsocketinthemiddleoftheshaft,thiscouldbeusedtoholdtheshaftinplace,butIfoundthatspinningthenutwiththewrenchquiteeasy:

Pullthepulleyoftheshaft,thereisawasheraboveandbelowthepulley,removeboth.Next,removethefourTorxscrewsontheplatebelowthepulley.Theseareverytightandhavebeenlockedwithathread-lockcompound.MakesurethattheTorxbitisaperfectfitbeforeattemptingtoremovethem:

RemovetheB+terminalandthenutbelowit:

Theblackcovercannowberemoved,thisisstuckinplacewithasealantbutcomesoffquiteeasily.Removethefourscrewsshownhere（pleasenotethatIdidthisincompletelythewrongorder,theblackcoverandpulleyshouldbeoffatthispoint）:

RemovethetwoTorxboltsthatareontheouterrimandthebackhalfofthealternatorcanberemoved:

Therotorcanberemovedatthispoint:

Thefaultwithmyalternatorwasarear-bearingfailure,ithasseized,overheated,andisnowstuckontheshaft.Iusedabearingpullertoremoveit.AreplacementisavailablefromBMW,itisa32mmx12mmx10mmgroovedbearing,BMWpartnumber12311739203:

Thefrontbearingislargerandcanberemovedwithapullerorknockedoutfrombehind.Itisa52mmx17mmx17mmgroovedbearing,BMWpartnumber12311747246:

Thealternatorhasnobrushestowearout,ifnooutputwasseenwhenthealternatorfailed,firstcheckthatalltheconnectionswerecorrectlytightened,Ihaveheardofthescrewsbeingloosethatconnectthefieldcoils.Theregulatorismorecomplicatedthanthatusuallyseenonastandardalternator,ithastheabilitytoswitchtheoutputcompletelyOFF,thisisdonewhenstartingthecarandwhenatfull-throttle,undercontroloftheDME.ItcanberemovedcompletewiththeconnectorbyremovingthetworemainingTorxscrews:

Theregulatorisavailableonvarioussitesbutisquiterare.Thesameistrueforthediodeblock.Whenreplacingthealternator,makesurethatthesealisintact,althoughshownasaseparatepartonrealoem,itisnotavailableandyouwillgetabagofthreesmallersealsinstead!

Carefullyremovetheseal,lubricateitwithsiliconegreaseandthenreplaceit:

Alldone,timeforacupoftea