piston problem HELP

[yamyrider]

Guys what is going on. This piston is from the exhaust side. The other two look new but this one is ugly. Opinions please

 

[yamaholic22]

That almost looks like a little bit of cold seizure. How does the intake side look?

 

[yamyrider]

the intake side is better but bot as good as the other pistons. This is the piston on the opposite side of the clutches.
Should I use the Yamaha or would an aftermarket be ok.
Thanks Holic.

 

[Ding]

Be sure to fix the source of the problem before putting a new piston in.

Show pics of the top and underside of the piston, as well as the other side.

 

[yamyrider]

here some other pictures.
The top look ok and some minor marks on the intake side. The worst is the exhaust side.
What should I be checking.

 

[Ding]

I would agree, a slight cold seizure. Looks like a little blow by was happenning also.

What is the history of the engine?

 

[yamyrider]

http://www.eric-gorr.com/tech/pistonguide.html

I would say four corner cold seizure according to the link above.
There are days when it is really cold and I strat the sled and drive it out of the gagare to let it warm up..maybe 25 feet. Could this have caused this problem.
Should I use the Yamaha part which my dealer has to order or is an after market (Kimpex) ok.

 

[yamaholic22]

It can also happen from say stopping to go sit in a restaurant for a little while or something, the coolant cools off very quick in the exchangers, you start it up and start cruising down the trail, those pistons heat up real quick but the cylinders stay cool until the coolant gets warm, and those pistons expand much faster than the cool cylinders, so there is where you get your seizure from. I have put some thermostats in the nonvalved triples with good results so far, no more minor seizure marks on the skirts. Temps are just too inconsistent without them.

 

[Ding]

Use OEM Pistons, I would not use the Kimpex ones unless you don't mind more frequent rebuilds.

 

[sxr700]

what thermostat do you use ???

 

[yamaholic22]

actually i had a couple out of 440 gpx's that i use

 

[daman]

There are days when it is really cold and I strat the sled and drive it out of the gagare to let it warm up..maybe 25 feet. Could this have caused this problem.

Mabie.......I don't move my sleads an inch until they've warmed up 10-15min.from dead cold