I pulled the y pipe off the exhaust and took a picture. The compression is getting low, 110 psi in each cylinder. The other piston looks great. I had a clogged jet in the carb. Has this piston been melted? Could it be to tight of clearance? It looks to me like the outer layer is peeling off all the way around. I am pretty sure these are wiseco piston even though the previous owner told me he had it rebuilt with oem pistons.
shaggyzr2
Active member
possible cold seizure.
Hard to tell from the side, top of the piston would tell you more. But I concur, cold seizure, or a possible lean condition from the plugged jet.
Thx for the replies. From what i could tell the top of the piston looks fine. It looks like I'll be tearing into this soon. I would imagine i will probably have a shot cylinder also?
With the piston looking like that, I would have to assume so. If you can feel scratches in the cylinder wall with your fingernail, cylinder will have to be re-plated. Sending mine in Monday ....
shaggyzr2
Active member
I can't say for sure that yours was a cold seizure but with wisecos you're more likely to have a cold seizure. They are forged pistons which expand faster than the OEM cast pistons, they can seize easier than a cast piston if you don't let the engine warm up good before taking off. If I were you I'd go with either an OEM or and SPI brand piston.
Actually, the factory Yamaha piston is "powder forged", and is excellent for not changing size based on heat and cold, unlike the wisecos.
I have always used the factory Yamahas in my rebuilds.
I have always used the factory Yamahas in my rebuilds.
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