ClassicMotorcycleMechanicsJune2020

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Simple solutions:Keepavarietyofwashers/shims:you'llneed'em!

Withthelumpsafelyensconcedinthe

warmembraceofthewidow-maker’s

frame,InoticedthatIhadforgottentofit

theoilsealforthegearchangeshaft.Oil

sealsaredesignedtokeeptheall-

importantlubricationfluidswherethey

shouldbewhenyouhaveshaftspassing

throughthewallsofthecomponent

containingthelubricant;inthissituation

itisthegearbox.

Therearevariousdifferenttypesofoil

seal,butthemostcommonarelikethe

oneinthediagramIhavedrawn.Thebody

ofmostoilsealsusedonbikeengines

tendtobemanufacturedfromnitrile

rubber,whichhasgoodresistancetoheat,

petroleumandhydraulicoilsaswellas

petrol.Nitrileisdesignedtooperatefrom

• 40 °Cto 120 °Candifyourengineisany
  hotterthan 120 °Cthenyouwillhavealot
  ofissues.Onthemostcommonlyfound
  sealsyouhavealipontheveryoutsideof
  thesealwhichjusttouchestheshaftand
  whosereasonforexistenceistokeepdust
  andgritawayfromthedelicateinnerlip.
  Theinnerlipisheldincontactwiththe

shaftperipherybyaspringsteelgarter,

whichiseffectivelyatoroidalspringwhich

exertsaneven,butgentleforceonthelip:

whenasealisholdingbackoilarounda

constantlyturningshaftlikeacrankshaft

orgearboxshaftitisofparamount

importancethatshafthasaperfectground

finish,otherwisethevulnerableseallips

willbeabradedbythespinningshaft

generatingheat.Forthesamereason

theseallipneedstobelubricatedbythe

oilbehindit.

Wherethereisn’tgreatlubricationthe

sealwillnotonlybedamaged,butrather

counter-intuitivelywillwearagrooveinthe

shaft,particularlyiftheshaftisn’tcase

hardened.Althoughthelippartsofthe

sealneedtobeniceandflexible,theouter

bodyneedstoberigid.Thisisachievedby

havinganL-sectionsteelsupport.When

thesealisdriftedintoitscutawaythe

steelreinforcementcausesthe

interferencefitoftheouterbodytobe

heldtightlyintheseal’sorifice,preventing

movementorleaksaroundtheseal.

WhilstIwillnotcompromiseonquality

materials,partsortools,Iamnotpartialto

being‘bentover’justtohaveapartina

boxwithanOEM(OriginalEquipment

Manufacturer)logoemblazedontheside.

Kawasaki,Yamaha,etaldonot

manufactureoilfilters,sealsbearingsand

thelike.Whentheydesignanenginethey

willlookatthespaceavailableandthen

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5/Attachingtheleft-handvalvetothecrankcasewithabitofWellsealtopreventany

potentialleaks.6/Aropearoundtheliftarmabovemybikebenchtotakesomeofthe

weightoftheengineunit,makingiteasiertowriggleintoplace.7/Abitofsupportfrom

abovemakeslifesomucheasier.8/Anicestoutwasheramillimetrethickwasaperfect

shimtomakeupforpiss-poormanufacturingtolerances.9/Pushingtheshimwasherin

betweenthelumpandtheframemountingplate.

90 /classicmotorcyclemechanics

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