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Crankshaft Damper

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Neko H, Sep 13, 2000.

  1. Neko H

    Neko H Registered Member

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    I just droped a rebuilt 400 small block in my 79 GMC Jimmy and it is working well but I seem to have a lot of play in the crankshaft damper.

    By this I mean with the engine running I can look down on it from the side and as it is rotating I can see the shadowing effect of it not being balances. Im guessing there is about a half inch difference in the rotation.

    What could cause this besides the crank shft being bent (which it should not be with this rebuilt engine. It this a potential problem or just normal?

    Any ideas or thoughts would be apperciated.

    Thanks,
    NekoH

    Neko H
    79 GMC Jimmy 4x4
    (If I'd only win the Lottery, it would be Cherry)
     
  2. Smitty

    Smitty 1/2 ton status

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    Is the dampner designed for the 400 or is it off of a previous engine of a different size. The 400's are balanced differently than the other smallblocks.
     
  3. Neko H

    Neko H Registered Member

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    The original engine was a 400 also so I did a 400 for 400 swap.


    Neko H
    79 GMC Jimmy 4x4
    (If I'd only win the Lottery, it would be Cherry)
     
  4. Smitty

    Smitty 1/2 ton status

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    Well that blew that idea out of the water!

    If there's a 1/2" difference in the wobble it shouldn't be too hard to find the problem. I'd take a look at the balancer first to see if the outside ring is comming lose from the center portion of the balancer. You'd be suprised how many new balancers are sold because someone dropped or installed one incorrectly. I've also heard of the rubber ring that is between the two pieces just falling to pieces.

    To check the crankshaft you need to use a dial indicator on the crankshaft to get a reading as someone turns the flywheel. This will need to be measured without the dampner in place. If the movement is as large as you say you might get away with a piece of wire mounted to the block to get a crude visual measurement.

    Just a thought....Is the shadow effect coming from the dampner or the pulleys mounted to the dampner? If it's coming from the pulleys it might be that something is between the pulleys and the dampner.
     
  5. BLK78BLZR

    BLK78BLZR Newbie

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    normal. thats how u can tell its a 400 balancer,by the offset on the outer ring. the offset is for the external balance. 350 balancer is completely round. if u had wrong balancer or outer ring has slipped on inner hub u would have a vibration BIG time.
     
  6. Neko H

    Neko H Registered Member

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    OK here is the deal for future reference.

    Thanks steve for the info.

    OK here is the deal for future reference. The 400 Balancer has an ofset on the back (Steve you were right). And I was seeing that offset on revolutions with out seeing the balancer as a whole. Thus the illuision that the whole balancer was about a quarter to half inch out of balance. Once I knew to look at the front portion of the balancer and take the offset out of the picture, it has no hop or play at all.

    So future reference, should anyone need it (who thinks they are seeing things like me).


    Neko H
    79 GMC Jimmy 4x4
    (If I'd only win the Lottery, it would be Cherry)
     

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