piston melted??????????????? pic

[250rice]

17181030261718103027 i am rebuilding my cuz topend right now and was wanting to see what caused this. was it to lean or overheating , over reving, bad rings or what just put a new piston in 3 weeks ago with a new bore now bored it out again and new piston. trying to figure it out so it does not happen again.

[250rice]

its done now. ill run it tomorrow and see what happens. if the weather is nice.

[headache]

looks like you need a bigger main jet! thats def from detonation. you may need higher octane fuel too. what all is done to the motor?

[250rice]

178main 50 piolet cgj needle. 330 esr topend 38mm carb vforce cr250r ignition. he uses pump gas also

[Pumashine]

No need to re-bore cylinder. Just needed a new piston and run on race gas.

[C-LEIGH RACING]

You can go to most any small engine repair shop & see this same kind of damage every day on small engines, and why is that, because of using pump gas & the engines not set up to use the stuff.

On any 2 stroke performance engine, race gas should be used.
I would not even recommend using pump gas in a stock OEM type engine, specially not pump gas with ethanol mix in it.
Neil

[250rice]

so he needs race is that what you are saying. he only had a few heat cycles and about a two hour ride on it. and about 30 min of the 2nd ride it went. i also told him not to bore it but he said it was messed up so he done it before i looked at it.

[C-LEIGH RACING]

When you think of gas, the octane level, the lower the octane level faster it will burn in the cylinder.
Like 87 octane will burn up way faster than say 100 octane, so when an engine is running on low octane, it burns up all the gas in the cylinder & super heats the edge of the piston & cylinder wall & by everything going out the exhaust, it really heats up those areas to the point of melting the piston.

Octane of gas used, needs to match up with the compression amount the engine has. Like around 170~180 lbs of compression, probably a 50/50 mix of straight 92 (non ethanol) & race gas should be used, just to slow the burn rate & keep from burning up all the gas in the cylinder.
When all the gas in the cylinder is burned up, it super heats the piston & will soon melt the piston, but if you can keep from burning up all the gas in the cylinder, that gas left in the cylinder that didnt get burned up will have a cooling effect on the piston.

This is one of the many reasons, I stress the point of running a 2 stroke rich as you can, as large a jet as the engine can use, because the richer the carb jets are, longer that engine will live.
Neil