excessive oil out breather tube

[hookedonpain]

Blowing out 1/2 to 3/4 of a quart between our two motos this weekend.No smoke coming out the exhaust,compression was just checked one race ago(supposedly).It does have 10 races on the 11:1 76mm piston. Any suggestions?

[m0t0xk1d]

At high rpm's your rings are not sealing and they are letting hot gases blow past your rings into your crank case causing high crank case pressure and forcing oil out your breather tube. Without knowing more about your engine, you either have cylinder walls that are scored or the rings are just worn out and it's time to re-build it. If your motor hasn't started to burn oil yet, it soon will because you are washing the oil off your cylinder walls with the hot gases passing by the rings. When you tear it down you will also want to check out your intake valves on the 300EX. The stock valve springs doen't let the valves float but at high rpm when they hit on the seat they bounce and it causes them to prematurely wear out. You will notice the 45 degree angle will be cupped on the valves and they will need to be replaced. It sounds like you just need a good re-build.


right form mickey dunlap

[hookedonpain]

Thanks,you hit it right on,there was a small score in the cylinder causing the blow by and crankcase pressure to build.