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  1. #1
    PWCToday Newbie
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    1999 GP1200 engine problems

    I just picked up a broke GP1200 as a project.
    I didn't know much about these but am starting to learn.
    the engine is destroyed, the rear cylinder is bad, broken crank, hole through crankcase.
    This seems common for this engine. Can anyone tell me why. What fails first?
    Thanks.

  2. #2
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    Re: 1999 GP1200 engine problems

    I was just thinking about my question above and I should try and be clearer. Not my strong point.
    I should have said "when an engine fails" the rear most cylinder seems to be effected first.
    I did not mean that it is common for the engine to fail, I really don't know how reliable they are if looked after properly.

    I have been searching and cannot find a reason why it is most often the rear cylinder. But someone must have ideas.
    Thanks

  3. #3

    Re: 1999 GP1200 engine problems

    rear cylinders tend to run hotter... the water is already hot by the time it gets there.. on the 760's they run bigger jets to help cool the pto cylinder.... also that is the cylinder that cranks seal is exposed.. the front one is covered by the stator cover.. it seems like that front seal always lasts longer..

  4. #4
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: 1999 GP1200 engine problems

    Rear cylinders usually run less compression and timing to try and compensate for crankshaft torsioning, which in laymans terms is twisting of the crankshafts. While all crankshafts have a certain amount of torsion under load, the longer the crankshaft the more torsioning takes place, this is especially true on three cylinder engines and is enough to change the timing on the rear cylinder to an unacceptable level.

    This is why Yamaha went to the lowered timing and compression on the rear cylinder of the 1200 engines. I do not necessarily agree with your assumption that is is always the rear cylinder that gets damaged , I have seen it on all of the cylinders. The main reason three cylinder engines substain so much damage is rather simple, it is because they have two other good working cylinders to drag the damaged cylinder to death, on a twin cylinder engine when one cylinder goes down it does not have enough power to continue running the Watercraft.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries


  5. #5
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    Re: 1999 GP1200 engine problems

    Thanks, my rear cylinder idea came from googleing, so i was hoping to be corrected. But the rear seal, hotter, and changing timing (from twist) all makes sense.
    Mine looks like the connecting rod bearing at the crankshaft was melted it got so hot, that affirms what is said above.

    So i guess there is really nothing i can do to stop it from failing again. Nore do i have to as after rebuild it will probably be fine.

  6. #6
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: 1999 GP1200 engine problems

    That really sounds like it had an air leak at the rear crankshaft seal causing it to run lean. It would really only affect the rear cylinder.
    Last edited by WFO Speedracer; 01-04-2018 at 07:53 PM.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries


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