Seals too tight on bottom end??

Discussion in 'High Performance Bicycle Engine Tips and Motorized' started by Wags, Aug 14, 2016.

  1. Wags

    Wags New Member

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    I'm rebuilding my bottom end. My crank spun perfect until I insalled the new seals. Now I have to use some pretty serious force to spin the crank. Is this normal? Please help.
     
  2. Kioshk

    Kioshk Active Member

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    You've attributed the issue to your seals; is the crank isolated from the drive-train? Is the engine completely reassembled? Is the resistance continual or intermittent?
     
  3. 2door

    2door Moderator
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    Something else is goin on. Crankshaft seals do not add that much rotational resistance.

    Even if you didn't lubricate the seals while installing them, they wouldn't keep the crank from turning as much as you describe. Keep looking.

    Tom
     
  4. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    Did you overtighten the 4 cylinder studs and crack the crankcase
    housing which is rubbing against the crank?
     
  5. allen standley

    allen standley Well-Known Member

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    Check shaft keys. If one has slipped too far back it will bind against that brand new seal.
    I had this issue with a half round shaft key, kinda banana'ed up at the rear and bound up the rotation.
     
  6. Wags

    Wags New Member

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    I had the whole bottom end put together. I decided to take one thing off at a time until I found the problem. It wasn't until I I got to the drive side seal that the crank decided to spin like it was supposed to all along. Now I know and I learned something new today ...that seals can be pushed in too far. Thanks for everybody's time.
     
  7. 2door

    2door Moderator
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    Not saying you're wrong but every engine I've seen has a shoulder machined into the case that the seal bottoms against. I've never seen one where the seal could be pressed in too deep. A seal with the wrong inside diameter, too small, could account for it however.

    Tom
     
  8. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    There are no shoulders on a Chinese bicycle engine.
     

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