SBT Jetski Engines, Parts & Accessories

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  1. #1
    Joined
    Jul 2005
    From
    Orlando, Florida
    Posts
    2

    Default Piston kit only or is there more?

    Hi all,
    My friend was riding my 95 SPX at full throttle crossing a lake here in central Florida. The engine cut out completely. Would not restart. Got some firing, but not enough to run. The back cylinder's spark plug was broke, changed plugs, still would not run. Did compression check, 70psi in the rear and 140 in front. I pulled the head and found the back piston began coming apart.

    So finally the question: Even though the compression was this bad, it seems the engine still should have run. Maybe poorly, but still run. Are there sensors in the exhaust or on the engine that may have detected a problem and turned the engine off?

    Thanks,
    Tom

  2. #2
    Joined
    Jul 2004
    From
    Carlsbad CA
    Posts
    147

    Default Re: Piston kit only or is there more?

    Why would you want to run a motor with a damaged piston. There are several reasons that it may not start. mostly mechanical in nature.

  3. #3
    Joined
    Feb 2004
    From
    New Jersey
    Posts
    2,601

    Default Re: Piston kit only or is there more?

    pull the head off and tell us what you see
    PRIDE IN SERVICE<br /> <img src="http://www.sbtontheweb.com/images/forposts/4609/1.jpg" alt=" - " />

  4. #4
    Joined
    Jul 2005
    From
    Orlando, Florida
    Posts
    2

    Default Re: Piston kit only or is there more?

    Thanks for the replies. I didn't want to run the ski once I knew it was damaged. At the lake we tried new plugs and it just would't run. Just curious why it wouldn't run.
    I have pulled the head and the back piston is missing about 1/16th of its top near the exhaust valve, piece missing goes lower than the first compression ring. So part of the top ring is missing.
    I don't know if the piston coming apart broke the bottom of the spark plug or the plug breaking cause the piston damage. The piece of the spark plug that was missing was the metal hook the comes down from the side of the plug.

    I was just trying to figure out if I had more problems then just a piston kit.
    Thanks,
    Tom

  5. #5
    Joined
    Jul 2005
    From
    NH
    Posts
    18

    Default Re: Piston kit only or is there more?

    I am just an amateur but I am fixing a ski that has a similar issue. I can tell you what I found when I pulled mine apart..

    Parts of the ring/pison broke off causing visual damage to the head. The same parts travled in to the rotary valve jamming the spinning valve which strips the brass gear and bent the shaft in my case. Once your timing is off the machine will not run at all....


    You have to pull the moter apart and inspect all components...

  6. #6
    Joined
    Nov 2003
    From
    Glendora, CA
    Posts
    6,846

    Default Re: Piston kit only or is there more?

    The piston came apart when the clyinder was not getting enough fuel, probably due to a clogged up filter inside the rear carb. That caused the clyinder to run too lean, overheat, expand into the exhaust port and break the top ring land and ring. The broken pieces smashed the sparkplug tip and most of them went out of the exhaust port into your exhaust system.

    You need a new motor and to rebuild your carbureators.
    Bill O'Neal <br>
    WCM
    <a href="http://www.watercraftmagic.com"

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