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06 yz85 piston slap?

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I have a 2006 YZ85 that has a knocking sound coming from the cylinder most likely. Its consistent with the rpms but it's not too loud, mostly noticable at idle. How can I tell if it's piston slap or not and what can I do to fix it?

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Usually 99 percent of the time piston slap is only on cold startup with a forged piston such as a wiseco. The forged piston takes longer to expand. The piston slap should go away when warm.

You said its a high Rpms so something is wrong. I'd tear the cylinder off before riding it anymore. These 85's need pistons anywhere from 15 hours for a fast rider to 25 max for a beginner. How many hours are on yours now? What kind of piston? Stock cast or forged aftermarket. Don't ride the bike until inspected! It could grenade

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Usually 99 percent of the time piston slap is only on cold startup with a forged piston such as a wiseco. The forged piston takes longer to expand. The piston slap should go away when warm.

You said its a high Rpms so something is wrong. I'd tear the cylinder off before riding it anymore. These 85's need pistons anywhere from 15 hours for a fast rider to 25 max for a beginner. How many hours are on yours now? What kind of piston? Stock cast or forged aftermarket. Don't ride the bike until inspected! It could grenade

I just got the bike recently but it was raced previously but I think it has a weisco piston. I plan on doing a new top end and getting the cylinder machined back to stock specs soon so hopefully that will solve my problem. What else could be causing it?

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You may be Pinging!

You can use a dial indicator to check the ignition timing and the Connecting Rod bearings at the same time.

 

Read the timing thread at the top of this forum (By Carver) and you will know all you need to know before you tear down.

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For a noise like that it either has to be piston/cylinder related or crank related. I own a yz85 myself with a 105cc forged wiseco piston and have no piston slap issues. Does this noise to away with the clutch pulled in?

Either way a rebuild is due. I'm not sure on what you use the bike for but instead of a stock bore replate and piston I'd recommend the eric gorr 105cc package for $425. Same price as a stock bore replate & piston but with more power and torque.

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