Light Scratches on Piston Skirts

I know with arctic cat the 800 and 900 have this problem becasue of the powervalves hitting the piston.

But I doubt yamaha would have the same problem.
 
i'd say from your piston rings being worn out it allows the skirts to rub on the side of the cylinder walls...I dont think it will hurt your performance any, I believe the compression comes from the piston head/rings..mayeb an over heat or bad oil would cause this too..
 
scratches are normal (within reason). they come from carbon that can be built up inside the exhaust and sucked back through the motor on the pulse coming back. on triple vipers with single pipe they can come from the exhaust pulse crossing over from the other cylinders.

run good oil and use some ring free regularly will give you less of this problem
 
As long as you can,t dig into them with your fingernail should be no probs.
 
yamyrider said:
http://www.totallyamaha.net/forums/showthread.php?t=16732

If they look like this that is some signs of cols seizure. I also had blowby.
Click to expand...


Yea theres diff. a bit of cold seizure but only where the wrist pins install at on both sides of the pistons. But the PTO has a scratch the my thrumb nail can pick up, can this end up damaging the plating on the cylinder???????
 
its not going to damage the plating but what I will do if the piston checks out size wise is just to use a small bit of 600 grit sandpaper and clean up the scratch very,very lightly, dont oversand it as your taking away piston material.
 
I have never micd one to see after it cold seizes because I usually just replace the picston as the damage would require it, I guess its possible but rather doubtfull, a cold seize happens very quickly and I wouldnt think the piston would be hot enuff to actually mold itself in a differnt shape, could be wrong because again, I havent micd a cold seized one.
Now I have seen pistons change shape after they have been run way to lean, they tend to want to shove themselves out the exh port when your talking full melt down!
 
I would have to agree there.
Cold seizure is something that happens ...well when the machine is cold.
My case with the pictures i attached is me starting the machine and hammering the throttle after about 40 seconds of running...NO GOOD.
Yamaha's need to warm up before the throttle is hammered.
I would not think that the piston would warp during that time.
I was lucky and only scored the piston without actually seizing the engine...BUT I did do it to my Indy 650. Started up waited about 30 seconds hamered down and about 150ft later engine seized. When I took it appart I could not see any signes of warpage but I did not measure either just inspected.
 
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