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  1. #1

    1999 GP800 - Motor Rebuild thoughts/advice - WITH PICTURES

    Hey everyone. Well I have recently acquired a 1999 GP800 that had motor issues. Before I started tearing into the ski, I tested compression. The back cylinder was 145, the front was 50. I was told that the ski was rolled upside-down, and then not rolled in the correct direction when rolling it back. He thought it ingested water. He was able to restart the ski and get it to shore and had it running back on land but it would never run right. I assume that when the ski rolled, it spilled most of the oil out of the tank, because there was a lot of oil in the bilge.

    Before I started to disassemble the ski I tried my best to test other functions. All the gauges seem to work, fuel tank is bone dry, coupler looks to be in good shape, electric box is spotless.

    I have since pulled the engine and clean the bilge and entire ski.

    When I pulled the engine I removed the head, carbs, exhaust, Reed cages, so I could see the extent of the damage. This is what I have found. As expected the front piston is torn up. It does not appear to be have cracks or hoes in the piston, but it is definitely torn up. The back piston seems to be in good shape. When I pulled the reeds, I found a lot of oil and metal pieces in the pedals. There is a lot of oil in the bottom of the crank case.

    The front piston rod bearing is missing "the bearing that the rod rotates around the crankshaft on". The rod is essentially rotating directly on the crank journal. I doubt it was run long if at all like this, but it cant be good.

    What do you think I should do? I was hoping to do a top end, but I dont think that would be wise not considering all the metal I have found and the crank bearing issue. Is this motor worth rebuilding? Also is there any marks or anything I need to make note of before I start tearing it down further? Do I need to mark exact bolt and which hole they came from? Thanks so much for your help, and sorry for the long post.Click image for larger version. 

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  2. #2
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    I would get some sandwich sized zip lock bags and toss the bolts in the bags with a label (like exhaust bolts, front cover bolts, head bolts, Etc). that way you can get them back in the same areas.
    Sounds like you need a crankshaft and a top end. I'd also suggest a carb rebuild while your at it. Also closely inspect the oil injection hoses and either replumb that system or block it off and premix the oil and gas.
    Becareful where you get parts from. Sometimes spending a little extra on good parts is a good idea.

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