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  1. #1

    Odd sound and problem with GP800X motor

    My GP800X quit on me, but did so strangely. The spark plug electrode was closed, i.e. the gap went away. It occurs at higher RPM's only. I've never seen that before.

    Here's the details of what I found when I tore down the engine, at least the top end. The piston was damaged, looked like some predet, broken lower ring, the other was stuck and didn't move easily. I didn't find metal fragments anywhere but I know they existed because the piston is missing a very small piece from its crown, about 1mm. The top of the piston has some small cup shaped indents in it as well, looks like something beat on it.

    The connecting rod bearings are good, but when I rotate the crankshaft, the rear cylinder, which is the damaged piston, has a noise that sounds like metal pieces falling. It occurs between the spot where fuel enters the cylinder and starts being compressed.

    I haven't worked on a PWC engine before so I don't know what the noise is and wonder can make that noise?

    The second question is, this was supposed to have been rebuilt about 30 hours ago, but there are no gaskets between the case and cylinder, yet parts diagrams show them. It was sealed with RTV. Is this acceptable? I'm not certain it wasn't just cleaned up and reassembled to sell instead of replacing parts.

  2. #2

    Join Date
    Sep 2013
    Bennettsville, SC
    You have found the reason for blowing the engine. Yes, a gasket goes there, and if it is not used, the piston goes too far up in the cylinder, hits the plug, detonation occurs, and the engine blows. If you know who rebuilt it, feel free to slap him.

  3. #3
    Turns out the problem was caused by a main bearing going bad and shooting a piece of metal up there. I'm going to order the main bearings, the oil seals, and an OEM piston ring set. Gaskets too of course. The cylinder head is a bit beat up, I'm thinking I should replace it because it looks like the surface of the moon.

    Looks like a fun project that I want to get done soon so I can Winterize it, LOL. Probably need to wear my drysuit on the ride...

  4. #4
    Just wanted to say that the Waverunner ran fine once I got it on the water. No problems at all to speak of. I broke it in and I'm very happy with how it's performing. When I did the rebuild I used OEM parts to repair it and didn't try to improve upon its performance. The hardest part of the entire project was removing the bearings from the crankshaft. Once I did that the rest was easy, except for a bolt I dropped in the bottom of the hull. They just don't give you a lot of space to fish around down there.

    It also sounds better than when I first got it, so to me it seems the previous owner stretched the truth or knew the engine was on its last leg because I can't think of a reason why the bearings would self destruct so quickly.

    I'm happy with it.

    Just updating the thread in case somebody googles it down the road and wonders if I fixed it. The forum was very useful to me in terms of how to rebuild it.

  5. #5

    Join Date
    Sep 2013
    Bennettsville, SC
    Glad you got it back on the water! The previous owner absolutely knew there were motor issues with it! I jumped on one sorta like that a couple months ago. I now have 2300 in a 97 venture 760. Face palm I know! But it's all wife likes it, as it's an upgrade from her 95 venture 701.

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