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  1. #1

    What caused this failure?

    Very low hour 97 900 ZXI. Under 30 hours. No compression on the MAG cylinder. Pulled it apart to find this. Honed the cylinder and stuck a standard bore piston and rings in it. I re-used the head which had pitting type marks all in it on that cylinder. Fully cleaned carbs (adjusted to factory spec) and removed oil injection as it had a line that looked like it was going to break soon.

    After break in it had 135 PSI on all cylinders. Never did rev up just right, had a slight delay/hesitation then would jump past and take off and run pretty good until you cut it off again. Then same deal. Carb adjustments made no real difference.

    A week later the jet pump went out. Fixed that and the delay/hesitation got worse. Very hard to get to WOT, had to play with the throttle and get it past that spot. Sometimes took 5-6 minutes. Still had 135 PSI compression at the end of all this and pistons/cylinders looked good.

    This is how the piston looked when I removed it. No metal found in the case either. I did not pressure test the case. My only though is an air leak, probably at the crank seal. What do you think?













  2. #2
    Which part of "there was nothing in the crank case" did you not understand? I did split the case and it was CLEAN! BTW I do not have this ski anymore so fixing it is not what I am after, just possible causes.

  3. #3
    Quote Originally Posted by sirbreaksalot View Post
    Dont ask question that you dont want answers too

    I have been building 2stroke/4stroke engines for 20 fking years, and every engine that shits it self like your did WILL have alloy fragment in the bearings

    were do you think the missing alloy went, into a box and shipped to the north pole

    obviously your knowledge is not that far advanced on 2 stroke engine .

    And it would of helped if you said I no longer own the ski, because then I wouldnt have wasted my time trying help someone that doesn't need it

    Waz
    Okay, well when I tell you the case was clean and that this engine has ran for over 14 hours since the repair I'd think the bearings are holding up fine. Obviously your knowledge of the English language is not that far advanced either.

    And no, I don't really need any help. This is just something that has had me wondering since I sold the ski. I rode it as is until I had the time to just do a full rebuild which I never got to do before selling it. If I still had it I would have pressure tested the case by now and have found my issue. Just been curious since I never did get to fix it.

  4. #4
    Quote Originally Posted by sirbreaksalot View Post
    Oh go beat your horse elsewhere

  5. #5
    Quote Originally Posted by sirbreaksalot View Post
    how many mechanics do you know that are English teachers
    The question is how many English teachers do you know that are mechanics?

  6. #6
    Wow! Im shocked that your bashing the guy for giving good and accurate information. In fact the only guy willing to give you help and you punch him in the mouth?

    That piston threw all sorts of metal into the cases. Sure it may look clean but Ill bet money that the crank is scorn on the big end. Any decent Mech would have sent the crank in for inspection and rebiuld. Its like a 150 bucks and its all new and fresh. You be surprised of the unseen damage of having metal shavings run through the crank.

    Maybe in the future talk to the English teacher about asking proper questions and what to expect the proper answer would be.


    I believe Waz is correct, typically the exhaust side "exhaust temps to high" gives out on lean running. If your using the original CV carbs and did nothing to fix the problem then it will happen again. Your slides is probably sticking open "CV Carb" or your jet is gunked up. The carbs need to be cleaned by a professional. You cant just spray carb cleaner in them and call it clean.

    Regardless if you dont know the cause and did a replacement then the cause is without out a doubt going to give another similar result.

  7. #7
    Moderator Insanediego Joe's Avatar
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    Quote Originally Posted by X-Runner View Post
    Which part of "there was nothing in the crank case" did you not understand? I did split the case and it was CLEAN! BTW I do not have this ski anymore so fixing it is not what I am after, just possible causes.

    Dude! Lets try and respond in a more friendly manner. Your the one that asked the question.

  8. #8
    Quote Originally Posted by Skips313 View Post
    Wow! Im shocked that your bashing the guy for giving good and accurate information. In fact the only guy willing to give you help and you punch him in the mouth?

    That piston threw all sorts of metal into the cases. Sure it may look clean but Ill bet money that the crank is scorn on the big end. Any decent Mech would have sent the crank in for inspection and rebiuld. Its like a 150 bucks and its all new and fresh. You be surprised of the unseen damage of having metal shavings run through the crank.

    Maybe in the future talk to the English teacher about asking proper questions and what to expect the proper answer would be.


    I believe Waz is correct, typically the exhaust side "exhaust temps to high" gives out on lean running. If your using the original CV carbs and did nothing to fix the problem then it will happen again. Your slides is probably sticking open "CV Carb" or your jet is gunked up. The carbs need to be cleaned by a professional. You cant just spray carb cleaner in them and call it clean.

    Regardless if you dont know the cause and did a replacement then the cause is without out a doubt going to give another similar result.
    Well the cause was assumed to be a dirty/clogged carb from the ski sitting up for so long. I have cleaned and rebuilt many carbs, they where cleaned properly. I have no idea how the ski ran before the failure so I can't say if there was a difference.

    There was no visible damage to the crank and the bearings were tight, the ski was a freebie that I did not want to spend much on because of hull damage on the bottom. I feel that any damage from metal going through the engine had no effect on the way it ran once it was put back together.

  9. #9
    seaobin's Avatar
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    Richard,

    What do you care? You sold a time bomb to some unknowing rider.

    But by the way you so graciously accepted the help you asked for, you would probably sell that machine to your best buddy and tell him it runs great.

  10. #10
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    In the event of a piston meltdown, I never ever ever ( did I say never?) just do a top end. Nothing good ever comes of it and most people around here own guns. They either go for a complete rebuilt engine or go elsewhere.

    btw, looked like an air leak to me.

    A wise man once said, he who doesn't determine the cause of a two stroke motor failure is bound to have it happen again and again and again.

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