<div class='quotetop'>QUOTE (rpyfz450 @ Mar 27 2006, 11:19 AM)
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Quote:
He's what I'm thinking...
When the exhaust edge of the piston crown has visable damage, it's usually because of excessively high combustion temperatures. This is probabaly from being too lean on the carburetor's main jet.
If you're too lean on oil, the cylinder bore would have dryed up a bit and suffered immediately. Coolant can also wash the oil away if it gets inside the engine. Do you still see the cross hatch marks on the bore?
The coolant you found may have just been from diassembling the top end, but it's important to do some foresics on the gaskets. Since this bike has done this twice now, someone should do a leak down test of the head/cyl/crankcase and also another one of the cooling passages. If coolant is getting inside the engine, it would most likely be from the base gasket. Also etheylene glycol burns bright white. Was this bike showing lots of white smoke even after it was warmed up?
How long has your buddy owned this bike, and does he know the full history behind it? Is it possible it has the wrong spark plug heat range installed? Is it possible ignition timing or compression has been altered?
Did this motor have a problem idling too high when in neutral (or clutch pulled in)?
What color is the piston crown?[/b]
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I can see some cross hatch marks toward the top but not much. I know the coolant spilled into the bottom end when I disassembled it. the bike does not show much white smoke after being warm if any. He has owned the bike since brand new. no problems idling too high ever. If piston crown is top of piston then it is black. so we are gonna put in a new top end and do you suggest putting a larger jet in.
thanks