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  1. #1

    Angry I rebuild my GSX-L 951 motor and it failed during break-in, help with post-mortem.

    I rebuilt the 951 motor, being very meticulous and followed the service manual. I added oil in the gas tank for the break-in 50:1. I took it out to the water and let it idle in the water for 15 minutes. then let it cool for 30, then cruised it at up to 2500 RPM and then let it cool again for 30 minutes. then cruised for 15 minutes up to 400 RPM and then took the ski home since it was getting dark. The next day I went out again and let it idle again for 10 minutes and then started cruising about 4500 rpms and the engine made a terrible noise and stopped. To speak of my level of ability, I rebuilt my 1999 BMW M3 motor 2 years ago and it's still running strong.
    I find it very peculiar that the sleeve split extremely evenly. Anyone have any postmortem insight as to what might have happened here?
    I would like to know what you guys think.


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  2. #2
    Banned User
    Join Date
    Dec 2006
    Crest Hill, IL
    Sleeve split good...How does the other one look?

    Looks like when it split it dropped down...

  3. #3
    Danny, the other side looks perfect.

  4. #4
    big john's Avatar
    Join Date
    Sep 2010
    Cocoa Beach, Florida, United States
    i agree with Danny, the sleeve cracked and slipped down, causing the top ring to snag, what a mess !!! the dreaded 951... i very carefully rebuilt mine, a few times before i got it right, mine had a bad carb that no matter what i did, it would lean out and melt a piston. good luck !!!

  5. #5
    I purchased the Cylinder block and the pistons from an out of state shop.
    I am looking for a little guidance. Does it look like the parts where defective? The way the sleeve split makes me think that it was...
    Should the shop bare some responsibility. I realize that I am asking a lot from just 2 pictures, but I also know that there are many of you that are very experiences and might have great insight.

  6. #6
    Banned User
    Join Date
    Dec 2006
    Crest Hill, IL
    Standard bore? or was it bored out?

    I would think they should bare some money back, or exchange towards a new set of jugs and other damaged parts...

  7. #7
    The bore was 1mm over

  8. #8

    Join Date
    May 2012
    Northern MN
    Sleeve might have been too thin in that area after the overbore, could have caused it to crack and drop.

  9. #9
    PEST!'s Avatar
    Join Date
    Jun 2008
    Rockledge Florida
    I have rebuilt many 951's with a 1mm overbore but never seen one do that. I have even seized two at 7500 on a modded XPL and never did that. Did you mic the cylinders and pistons to see what you were workin with? 951 is just an engine if built right works for a long time do it wrong and it isnt forgiving. What about your crank? it could have had bearing failure that would cause most of that damage and the rest could have been from the carnage it caused. In fact a broken or miss-installed ring could do all that. SBT bores all their engines to 1mm.

  10. #10
    kaotic1's Avatar
    Join Date
    Aug 2013
    That looks like detonation due to a lean fuel condition causing the piston to swell until a ring hung the port...I would pull the carbs and go through them very carefully looking for blockage or bad fuel pump diaphragm, sorry about your damage man 2- strokes are very sensitive to the small issues especially the i said problem is probably in the carb

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