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  1. #1
    I'm a water dude, jetski's, and water pools!!!! Joel22190's Avatar
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    GP1200r Engine Rebuild??

    First issue of the season and need a little help guys. I'm not sure what happened, but I lost all power when riding so I took her home and tore her down. I found that the first piston had been slamming into the plug. The cylinders and head look fine, but when I got to taking the piston off the bolt holding it on was bent. The crank arms look fine and they all move freely. What could of caused this damage, and should I replace the crankshaft while I have her taking apart or just replace the pistons and gasket? I found a engine rebuild kit that includes New Crankshaft, All Pistons, Top End Bearings, Complete Gasket Kit & Crankcase Sealant for $561.00. Does this seem like a good deal and What is the difference between piston sizes?
    Rebuild Kit- http://www.atlanticjetsports.com/sta...s_-_yamaha.htm

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  2. #2
    I'm a water dude, jetski's, and water pools!!!! Joel22190's Avatar
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    More info- I'm already running premix so it was not a oil problem and the pistons were still attached to the crank arm so the c-clips were all fine. Could this still have been a Carb issue when running premix?

  3. #3
    TX21's Avatar
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    The price is way off, the site you linked dosent even show a 1200 power valve kit. The crank alone is I think $500. Pistons are gonna be over $100 per so figure like $900 (+/- 200) or a full rebuild and thats if the cylinder walls are ok. And there is no bolt holding the pistons on. It is held onto the crank by a wrist pin with c-clips so are you saying that wrist pin is bent?

  4. #4
    All hail the Chief! fullboogie's Avatar
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    Do a search on AJS. Not good.

  5. #5
    I'm a water dude, jetski's, and water pools!!!! Joel22190's Avatar
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    The crankshaft and cylinders all look fine, all I'm going to do is replace the pistons and gaskets, and get the carbs rebuilt. Let me know if there is good place to find economic pistons. Also what's the difference between piston sizes?

  6. #6
    TX21's Avatar
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    Quote Originally Posted by Joel22190 View Post
    The crankshaft and cylinders all look fine, all I'm going to do is replace the pistons and gaskets, and get the carbs rebuilt. Let me know if there is good place to find economic pistons. Also what's the difference between piston sizes?
    OEM Yamaha, Pro-X or WSM pistons. And you answered your own question about the difference in piston sizes.

    You still didn't tell us what was bent.

  7. #7
    I'm a water dude, jetski's, and water pools!!!! Joel22190's Avatar
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    I believe the wrist pin is bent just because it is tighter and harder to get out than the other wrist pins. And can you please enlighten on the piston sizes.. Thanks

  8. #8
    I'm a water dude, jetski's, and water pools!!!! Joel22190's Avatar
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    So Ive done a complete top end engine rebuild with wsm pistons, all new gaskets, the cylinders honed, and the carbs rebuilt. I also replaced the bendix and the starter clutch while I had the engine out and got a new battery. So far I have spent around $850 on my ski this summer and it is still not running right. It sounded fine on the trailer when I dropped the engine back in, but I brought it to the water I got no power to the impeller when accelerating. If anyone knows what the problem is or a good mechanic I could bring it to on the space coast of Florida please let me know. I'm sick of looking at my toy in the garage. Also my fathers 2000 seadoo rx needs a new engine and we have no idea where to get one. So any info there as well.

  9. #9

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    Quote Originally Posted by Joel22190 View Post
    ........I found that the first piston had been slamming into the plug. The cylinders and head look fine, but when I got to taking the piston off the bolt holding it on was bent.


    What could of caused this damage, and should I replace the crankshaft while I have her taking apart or just replace the pistons and gasket?
    [/SIZE]


    I did not see where you addressed the bent plug issue. A bent plug is not normal and an indication that you may have a crank problem. Did you check into this before you put it back together?

  10. #10
    Happily Self-Employed WFO's Avatar
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    PM member Duke in Titusville or Jim's Performance in Tampa for help

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