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  1. #1
    Dirtfishing's Avatar
    Join Date
    Aug 2018
    Ashland, Ohio

    What do you think would have caused this damage?

    I bought a 99 XL760 Waverunner this past weekend knowing that it had compression problems. I got the motor out last night to find this...I pulled the two small parts out of the bottom end with a magnet and I think they look like the parts that keep the ring from moving. It is just strange that both top rings were out. How does this happen? I guess it is time to start sourcing some used parts for this Winter project. I believe I will be going to premix and a block off plate just is case the pump had something to do with this. Any ideas as to why this would have happened?
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  2. #2
    butterbean_29512's Avatar
    Join Date
    Sep 2013
    Bennettsville, SC
    High hour motors do occasionally lose a ring locating pin. The oil pump had absolutely nothing to do with it. A super hot lean fuel mixture will cause the pin to.dislodge. Your piston is destroyed....hard to tell if you lost a pin just because, or it came out because of overheating. Lastly...don't look like the other chumps pouring oil in the wrong hole just because you misdiagnosed your failure.

  3. #3
    Outboardjohn's Avatar
    Join Date
    Nov 2017
    Escondido, Ca. 92026
    IMO oil pumps rarely fail, I personally would leave the oil pump on, just me.

  4. #4
    Dirtfishing's Avatar
    Join Date
    Aug 2018
    Ashland, Ohio
    Good to know you don't think it was the pump. I will look into keeping it.

  5. #5
    I worked on several older gp 1200's that had loose ring locating pins. They were low hour engines also. I read somewhere that stock Yamaha Pistons had this problem. The aluminum piston expands quite a bit at operating temp and the small stainless pin does not. I had a couple perfect used Pistons that I would use because of loose pins.

  6. #6
    steve45's Avatar
    Join Date
    Feb 2008
    The oil system is about the most reliable part of the boat--after you've upgraded/secured the oil lines.

    The beauty of the Yamaha lube system is that it dumps oil into the carb throat, even if the fuel flow gets plugged.

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