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  1. #1

    When to consider a top end?

    Just a question for the experienced two stroke guys, when do you start considering a top end? Do you look for a certain level of compression? Do you wait for degrading performance or hard starting? Or do you wait until something bad happens? The reason I ask is that I have a fair amount of experience with two stroke MX bikes and I was putting rings in them all the time. I've had my ski for a few years now and I haven't touched the engine, so I'm naturally worried.


  2. #2
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    I say as long as its running well keep riding.

  3. #3
    When the compression drops

  4. #4
    steve45's Avatar
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    I think a reasonable life expectancy for the thin chrome rings on these engines is about 200 hours. I wouldn't push it past that, even with good compression.

    It seems that when you get that many hours on a piston/ring, either the piston breaks or the ring is worn enough to rotate and catch in a port or something. Not worth the risk, in my opinion.

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    My understanding when you start seeing greater than 5% difference in compression between any of the cylinders, you should consider it. Anything close to 10% variance and you definitely need a rebuild. If your ports have been properly chamfered and whatnot, you have less risk of the ring "catching" from wear, but they do wear down. Being as you have experience with 2 stroke motocross, you know how the engine should feel performance wise to tell you something's out of whack. But definitely check compression. On my 2001 ZXi, I believe the target compression is 130psi... 120psi and you should be just fine, but getting down close to 100psi and that tells you things are leaking and not right, which you should definitely see a performance hit if that's the case....

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    Quote Originally Posted by MacAddict View Post
    My understanding when you start seeing greater than 5% difference in compression between any of the cylinders, you should consider it. Anything close to 10% variance and you definitely need a rebuild. If your ports have been properly chamfered and whatnot, you have less risk of the ring "catching" from wear, but they do wear down. Being as you have experience with 2 stroke motocross, you know how the engine should feel performance wise to tell you something's out of whack. But definitely check compression. On my 2001 ZXi, I believe the target compression is 130psi... 120psi and you should be just fine, but getting down close to 100psi and that tells you things are leaking and not right, which you should definitely see a performance hit if that's the case....
    Precise tolerances

    Last edited by ange5583; 05-20-2014 at 04:15 PM.

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    So i don't upset people I'll remain silent
    Last edited by ange5583; 05-20-2014 at 04:16 PM.

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    steve45's Avatar
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    Quote Originally Posted by ange5583 View Post
    So i don't upset people I'll remain silent
    What's that about?

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    Quote Originally Posted by ange5583 View Post
    So i don't upset people I'll remain silent
    But you didn't remain silent and that is what is upsetting. If you have some useful knowledge to impart upon us please by all means share

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    Quote Originally Posted by xxx2 View Post
    Quote Originally Posted by ange5583 View Post
    So i don't upset people I'll remain silent
    But you didn't remain silent and that is what is upsetting. If you have some useful knowledge to impart upon us please by all means share

    Keeping within 5% you would spend more time overhauling engine than riding your ski.

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