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Old 06-23-2009, 09:41 PM   #1 (permalink)
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Join Date: Jun 2009
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Default GP1200R new piston destroyed

I have noticed quite a few posts on gp1200r eating pistons. What causes this. I have a ski with a little over 100 hours on it and it sounded like some piston slap in the motor. So I pulled it down and checked the cylinders which seemed ok but the pistons were worn. I put in three new pistons and first time out the center piston is destroyed, hole burned through the exhaust side and top of piston next to exhaust port looks burned. I used all new gaskets and the other two pistons look ok. I guess I will have to get the center cylinder sleeved. Should I do them all or can some tell me what usually causes this.
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Old 06-24-2009, 09:15 AM   #2 (permalink)
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Location: Australia
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The 1200P/V motor runs about 2-4thou clearance. I have tried that many pistons in stock skis and nothing compares to the genuine Yamaha pistons and barrels. If you have your barrel re-nickalsiled you may have a problem. The nickasil just seems to peel off on the exhaust side no matter how rich you run it. OEM is expensive but they come with a size matched piston and WORK. If you are running OEM and it is failing check the power valve adjustment and carb settings. The fact that you have recently replaced the pistons to me means you may have installed the rings upside down? And don't get re-sleeved barrels for those motors, I can tell you a hundred reasons but they just don't work! Trust me, I have done hundreds of those motors!
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