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  1. #1

    Foreign object, or piston meltdown?

    This is on my JS440, but seems to be a general 2-stroke question and here I'll actually get responses. I'd appreciate any opinions or insight into this. Here goes...

    Rebuilt the carb over the weekend, reinstalled with original mixture settings. While single carb was off, intake was sealed up with tape. Today while running at near top speed, the ski started sputtering and gradually died. Back at home I've taken a look at it and things look pretty grim. I'm not too worried about it as I've got a spare motor to throw in, but I'd like to have an idea of what caused this. Piston washes WERE looking good, no hesitation across the board, and the other piston still looks good. Pictures below are the offending cylinder.

    Spark plug had metallic grit on it, cylinder wall had one score that you could feel, and piston top and head look to have taken a beating. AND here's the clencher.... piston is disconnected from crank. It seems that the connecting rod is detached right under the piston because I can move the piston back up with crank rotation, then I can push it down with my hand without much force. Possible that something made it down the intake while the carb was off, and somehow made it up into the cylinder? Or maybe something on the lower end died and made it up there. Or, broken piston ring or melted piston. The damage especially to the head make me say foreign object, but internal or external. Hmmm.... Opinions?







  2. #2
    ph2ocraft's Avatar
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    Bearing/bearing cage fell apart??
    Maybe just due to age??
    How many hours on the engine?

  3. #3
    Connecticut CrazyA's Avatar
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    Looks like needle indentations from crank bearing(s)

  4. #4
    Well honestly unknown hours on the motor. Bought the old ski for nothing, did some of the basics so it would run well and just had some fun with it. In the purchase I also got a spare motor, so if that checks out alright then I'll throw it in there, no biggie.

    This is VERY possible due to age. The ski is a 1980, and the guy I bought it from said "well, it runs awesome and I think it was recently rebuilt about ten years ago." Haha recently? Eh, oh well it was a steal. The motor ran, and I've satisfied my curiosity with standups. I think it was a combination of age and that the motor seems to have had many modifications done. It absolutely screamed on the water, until now. I'd just like some comfort that it might be isolated to a failure within this motor, and not a fueling issue. Honestly though, the honeymoon is over and I'm thinking I'll get this thing up to 100%, sell it, and grab me an x-2 or waveblaster with the extra cash.

  5. #5
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    If the piston won't be pulled down by the crank then the rod has failed (broke)somehow,I agree it looks like needle bearing imprints,My guess is a wrist pin bearing.Non fuel related.Is this a premix ski?

  6. #6
    Moderator beerdart's Avatar
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    Definitely FOD damage!!


  7. #7
    Yep it's a premix ski. Oil injection hadn't come around yet when this ski was built. Concerning the broken rod, I suppose it resulted from the piston impacting all the foreign material up top?

  8. #8
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    You'll have to open it for sure,If you find the bearing wipped,then thats the FO. My thoughts lost a bearing and it got suxed into the cylinder.

  9. #9
    ph2ocraft's Avatar
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    Quote Originally Posted by mystahagy View Post
    Well honestly unknown hours on the motor. Bought the old ski for nothing, did some of the basics so it would run well and just had some fun with it. In the purchase I also got a spare motor, so if that checks out alright then I'll throw it in there, no biggie.

    This is VERY possible due to age. The ski is a 1980, and the guy I bought it from said "well, it runs awesome and I think it was recently rebuilt about ten years ago." Haha recently? Eh, oh well it was a steal. The motor ran, and I've satisfied my curiosity with standups. I think it was a combination of age and that the motor seems to have had many modifications done. It absolutely screamed on the water, until now. I'd just like some comfort that it might be isolated to a failure within this motor, and not a fueling issue. Honestly though, the honeymoon is over and I'm thinking I'll get this thing up to 100%, sell it, and grab me an x-2 or waveblaster with the extra cash.
    Check out a Hurricane.

  10. #10
    ph2ocraft's Avatar
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    Quote Originally Posted by beerdart View Post
    Definitely FOD damage!!

    Damn BD, what took out the turbine and do they try to repair it or replace that mega dollar monster??

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