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  1. #1

    2003 GP800R Top end Rebuild

    2003 GP800R - had low compression on rear cylinder. Front was ok (about 130's if I remember correctly). Re-bored and replaced piston, rings, etc on the "bad" piston. Now I'm measuring about 105-110 on both cylinders. My first thought was bad gauge (Autozone rental), but took it on the water and no power. Will barely plane out. Before I crack it back open again, is there something else you all would say to look at?

    I bought a complete gasket kit and replaced on both cylinders. Did not mess with the "good" piston as it measured ok on the compression test originally.

    Head gasket seems ok. There is a bit of water in the hull after riding...I ran it first on the hose and got some there too. Not alot, but definitely wet.

    Also, the power valves were literally gone when I disassembled the first time. So I 've replaced both of them with new.

    FYI, the original cause of the bad piston was one of the oil lines leaked/broke/loosened and I had 2 cycle oil all over the bottom of the hull. I used a block off plate (not because I wanted to, but because the mounting ear on the oil pump broke when I was reinstalling). Using 40:1 premix now.

    Thanks in advance for your help! - Andy from Indiana


  2. #2

    Join Date
    Jul 2019
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    Buffalo, NY
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    Did you pressure test the engine before running it?

    Also, there’s a break-In procedure for a new engine.

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