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  1. #1
    Albinomonkey's Avatar
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    New Piston and Rings, Low Compression

    I recently had a piston go out on my 1994 Polaris 750 SLT. This is my first piston replacement on a ski. I replaced the piston with a new standard bore piston, and I replaced the cylinder with a lightly used cylinder that had been miked and honed by a professional PWC mechanic. I made sure to align the rings per the manufactures instructions. All of the gasket surfaces were cleaned , and new gaskets installed. After I torqued the head and cylinder down, I ran a compression test to see what I was getting. I am only showing 35 psi. I know that I need to seat the rings, but I am concerned that the compression is too low, and that I may be missing something.

    Any help would be appreciated.


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    What are your ring gaps?

    What's your piston to cyl wall clearance?

    Welcome to the Hulk BTW.

  3. #3
    burtonrider10022's Avatar
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    Is your battery good?

  4. #4
    BlueFishCrisis's Avatar
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    Welcome to the Hulk! Definitely check your ring gap clearances. There have been issues with rings being sent out with improper gaps lately.

  5. #5
    Albinomonkey's Avatar
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    Quote Originally Posted by xlint89 View Post
    What are your ring gaps?

    What's your piston to cyl wall clearance?

    Welcome to the Hulk BTW.


    Glad to be here! Thank you for the help. I will check the gap and clearance in the next few days. Didn't think to check it (Rookie Mistake). It was also suggested to me that I may just need to run it a little bit so the heat can expand the rings. Is that a good idea, or is my compression reading way too low for that to work?

    Thank you again.

  6. #6
    BlueFishCrisis's Avatar
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    Way too low. Don't really think it will even run that low. check you gaps by installing the rings only (no piston) in the cylinder, then push the ring down a little with the top of the piston upside down in the top of the cylinder. Use a feeler gauge to check the gap.

  7. #7
    Albinomonkey's Avatar
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    Quote Originally Posted by BlueFishCrisis View Post
    Way too low. Don't really think it will even run that low. check you gaps by installing the rings only (no piston) in the cylinder, then push the ring down a little with the top of the piston upside down in the top of the cylinder. Use a feeler gauge to check the gap.
    Thank you for the procedure. What are the accepted tollerences for gap and clearance? Also, do I need to use a new head gasket, or is it ok to reuse the one I just put on?

  8. #8
    BlueFishCrisis's Avatar
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    .008 - .018. You can try reusing, most will use Permatex copper gasket spray on the head gasket when reusing to ensure a good seal.

  9. #9
    Albinomonkey's Avatar
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    Found the problem. When I pulled the rings, I found that I had broken the bottom one. I should have realized it was taking too much force to get the cylinder on.

    I noticed a couple of you are from the Cleveland area. Do you know any places that stock these rings localy?

    Thank you again

  10. #10
    BlueFishCrisis's Avatar
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    Not that I know of. Probably going to have to order them.

    Where do you usually ride??

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