oil seal orientation question.

Discussion in 'The Garage' started by stainlesscycle, May 8, 2012.

  1. stainlesscycle

    stainlesscycle Long timer

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    ok, so i'm putting new seals in a 2 stroke bottom end. it's 74 puch 175, and it's built a bit different then everything else i've worked on. normally i would place the seal lips facing the crank, and that's the way they were oriented when i split it (it's been opened before sometime in it's life). BUT the manual clearly states "large seals lips must point to the bearings" BUT the parts fiche (see pic) shows them oriented with lips facing the crank. obviously seal1 lips has to face toward the bearing. oh and before i split it i was wondering how the hell the ignition side bearing got lubrication (normally the dry side bearing in 2 strokes gets lubed with pre-mix) both bearings on this motor gets lubed from the gearbox - they cut a channel behind the bearing to feed it oil.


    so do seal2 and seal3 go lip towards the bearing or crank? since neither bearing is lubed via pre-mix i would think the lip faces the wet side(bearing). but every 2 stroke i've ever done i put the lip toward the crank (and normally the bearing is inboard, and the seal outboard).. since the the seal works off pressure, and the crankside gets both negative and positive pressure.... but on this bottom end neither bearing gets lubed with pre-mix. so do the seal lips go towards the pressure (crank) or the fluid (bearings)??

    had to split cases to replace seals, so i'd like to get it right the first time.

    a picture helps.

    [​IMG]
    #1
  2. motu

    motu Loose Pre Unit

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    Yes, you are sealing the crankcase from gearbox oil, so sealing lip to bearing...or flat side to crank if that sounds better.
    #2
  3. OldPete

    OldPete Be aware

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    Having only resealed a Yamaha and Hodaka,
    i'd say toward the crank because positive pressure is higher than negative pressure.
    #3
  4. stainlesscycle

    stainlesscycle Long timer

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    hah! 2 replies, and both different.

    ultimately what it comes down to is this:
    do you place the lip toward the oil, or toward the pressure. on a normal bottom end it's kinda obvious. this one is different. if the lip is towards the bearing, won't the crankcase pressure end up fouling the gearbox oil (and the bottom end leakdown would suck). if the lip is toward the crankcase, the oil from gearbox could migrate to crank on every upstroke...

    also if i put the lip toward the crank, as it was when i took it apart - it will be a bitch to install...very little surface on the lip side to push them in.
    #4
  5. OldPete

    OldPete Be aware

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    Most any bearing house can supply you with a double lip seal that seals both ways.
    I'd smear some light grease between the seal's lips.
    Install with the major lip toward the crank case.

    Measure shaft size, OD and width, order seals for high temps... like Viton.
    #5
  6. stainlesscycle

    stainlesscycle Long timer

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    yes, i'm familiar with seals... i already have them in hand. double lip, but adl/hmsa10 style - just a wiper and a major seal.
    #6
  7. OldPete

    OldPete Be aware

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    A wiper is there just to keep dirt from getting to the seal in an open air application. It offers no real sealing ability.

    A pair of double lip seals can be had in my area for at the most $20.

    The gear box had better be vented and as such offers no real pressure on the seal.

    My $0.02 anywho.

    EDIT: The oil squirting out of the ball bearings at the seals could offer some pressure... I'd still go double lip.
    #7
  8. stainlesscycle

    stainlesscycle Long timer

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    i already have seals, in the only design available at this size (ADL/HMSA10 DIN3760 etc..).. seals that were in it were single lip. both bearings get splash lubrication. gearbox is vented.

    [​IMG]
    #8
  9. OldPete

    OldPete Be aware

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    Ask in the 2 smokers forum.

    Not an easy call for nit-pickers like us. :lol3
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  10. ragtoplvr

    ragtoplvr Long timer

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    The lip would face the crankcase. You need to keep the pressure in there so you can run the engine. Leakey seal 2 strokes are very hard to start and low on power.

    Rod
    #10
  11. greywolf

    greywolf Unpaved road avoider

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    It looks to me like the seal orientations are shown in the fiche diagram.
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  12. stainlesscycle

    stainlesscycle Long timer

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    yes, it looks that way doesn't it.

    :rofl
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  13. concours

    concours WFO for 41 years

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    This is the right answer. The manual can be, and in many vintage cases is wrong. (DAMHIK)
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  14. wairau

    wairau south pacific vagrant

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    Agree with this. Any leak from the crankcase will cost power.

    The higher crankcase pressure will also prevent oil ingress from the gearbox oil.
    #14