Piston Failure Diagnosis Kawasaki 1200CC
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  1. #1
    PWCToday Newbie
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    Piston Failure Diagnosis Kawasaki 1200CC

    Looking for some advice as to why the #1 cylinder piston came apart on a Kawasaki 1200cc. The piston broke up and a piece of it was blown out the bottom of the case by the crankshaft.

    Quick background. Ski had run great recently. Several trips putting multiple hours on it no problems as all. Smooth crisp riding. I am then told it was run aground and got stuck in the sand. The ski was left stuck for a brief time and then pulled out and ridden 10 minutes back to the boat ramp. Next day it was ridden approximately 20-30 minutes and then died. After restart a loud pop as the bottom of the crankcase got a new hole in it. This is the story being reported back to me. I was not present for any of this.

    To me this timeline make perfect sense with the cooling system being loaded up with sand when stuck. The ski ridden 10 minutes back to the ramp, enough to get warm but not do major damage yet. Then the next day it was ridden until it melted itself all the way down. A piece of the piston is missing right at the exhaust port, the hottest part. My thought it that it overheated, was continually run and the piston cracked and then started coming apart due to overheating. Pieces of the side and skirt fell down in the crankcase and the crank soon ejected them.

    The oil line to the number one cylinder was still attached to the oil pump and had oil in it. I do not think it was a lubrication failure. When I got pictures of the motor removed one of the oil lines to the rear crank was off the nipple at the oil pump but I don't think that had anything to do with the failure. Seems more likely it came loose when engine was pulled.

    From these pictures does this make sense to you? Ski was running great and then boom just grenaded itself. It being stuck in the sand just prior to this happening is the one thing sticking out to me here. Everything was fine before that and I don't see evidence of this being a oil or fuel issue.

    Thoughts?

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  2. #2
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Piston Failure Diagnosis Kawasaki 1200CC

    It definitely overheated after the sandbar. The pump forced sand
    into the cooling line and it overheated and may have seized as a
    result. After the initial seizure it probably seized several times, and
    then started detonating and running on only 2 cylinders. The piston
    crown still has residue from detonation, and in order for the
    piston crown to melt, preignition occurred.

    On a 2 cylinder, the engine would have stalled 5 to 10 times or
    more (So long as the engine restarts, people keep riding and only
    stop riding when the engine will not restart) . But maybe because
    it is a 3 cylinder, and has more power people don't seem to notice
    the lost power, and keep riding it.

    Between the detonation and piston damage, the piston skirt
    broke, and got stuck in the case before the rod forced it out
    the bottom of the case.


    There is a chance the cylinder can be saved. Nikasil cylinders
    can take a lot of damage before the loose power. Most of the
    damage will be aluminum stuck to the Nikasil, and can be
    removed. Some scratches or gouges can be ignored.


    The oil pump on the Ultra is a benefit, not a liability.



    Bill M.

    When something goes wrong, people tend to be more optimistic
    if the engine restarts.

    Inspect the entire cooling system before assembly for residual
    sand.
    Last edited by wmazz; 07-26-2022 at 04:36 PM.
    Horsepower == Speed, RPM != Speed



  3. #3
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: Piston Failure Diagnosis Kawasaki 1200CC

    I agree with Bill. Also I can plainly see the burnt paint at the #1 exhaust port on the manifold......it was running VERY hot. This is a known issue on the Kawi 1200's as the water bypass fittings on the heads are 90* elbows and can plug up easily.
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    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

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    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

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