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  1. #1
    qbzonk's Avatar
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    restoring low compression

    My 98gp800 seems to have lower than normal compression between the 2 cylinders. The difference between the 2 is greater than 10%. I have 125 in the front and 140 on the rear.

    What exactly would I need to do in order to get my compression back to normal? Can I simply hone the cyclinders and get new, slightly larger rings and get the head checked or do I need to do more?

    I just want to get a general idea and cost of what to expect should I go this route.

    Thanks


  2. #2
    oldmanraider's Avatar
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    qbzonk,

    Your compression is not that bad so you should be able to get away with a hone and new rings.

    You should pull the head and take a look in side. If the walls don't look to bad you can get a way with a light hone and new rings. When you pull the cylinder assemble off you can check out the piston to find out if it needs to be replaced.

    If things look bad you will have to bore up a size or two and replace both pistons and rings.

    Matt

  3. #3
    qbzonk's Avatar
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    So I have to remove the cylinders from the block then correct? I'm assuming I will have to remove the engine from the ski in order to slide the pistons back into their respective jugs from the top after any honing is done right (like a car engine)?

  4. #4
    Flying Scotsman's Avatar
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    Its easier to do it with the motor out

  5. #5
    cheatin' piston popper addicted's Avatar
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    And you can't just bore them or hone them. They are nikasil plated aluminum. The need a special hone, and if you do bore them, they need to be replated. look up any posts on doing this on a GPR. same deal.

  6. #6
    qbzonk's Avatar
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    Quote Originally Posted by addicted View Post
    And you can't just bore them or hone them. They are nikasil plated aluminum. The need a special hone, and if you do bore them, they need to be replated. look up any posts on doing this on a GPR. same deal.
    Guess i'll be taken it to a pro for this job.

    Thanks for the help guys.

  7. #7

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    Its not usual for the cyl to be damaged on those, you may just need to pull the cyl, the pistons stay connected to the rods, and come out the bottom, put new rings on, make a light pass with a hone on the cyl, and your good to go. It is complicated though due to the power valves and exhaust removal to get to everything.

  8. #8
    qbzonk's Avatar
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    Hmmm. Not worried about removing the exhaust or PVs, that's not hard for me. I guess I'll ride it as is for the rest of the season and then tear it apart over the winter and see what's going on inside.

    I'll post pics when I tear into it.

    Thanks for the info gentlemen.

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