Ok so monster has been always doing that but it seems to have gotten worse. Whenever I have oil what appears to be at correct level in engine it dumps a lot of it back to airbox via expansion tank. It happens at mid to high rpm. When oil level settles to what appears to be way below minimum (just barely visible on sight glass) it stops doing that. Topping it back up will result in oil dump to airbox. There seems to be no oil starvation in engine as it done over 6k miles like that and did not go pop yet. What could be the issue? I am thinking my one way return valve at bottom end is blocked or there is an air bubble somewhere in engine that prevents proper oil reading on the bike so each time I fill it up to "correct" level it is actually over so it dumps it all. Any suggestions?
have you got standard engine breather setup? What you are describing is sounding ominously like early piston ring wear causing crankcase compression. Constantly running overly rich at top end will also cause this though so needs investigating. When I used to run even older - old bangers (4 wheel) than I do now, the only option was to keep oil level constantly low in sump to avoid the hefty consumption.
You tend to get it on race bikes where they are high revving for extended periods. That's why they use a different breather valve, which is not really a valve at all. It lets the oil flow freely in and out, but needs a larger capacity breather tank. It sounds like you have either got a faulty valve or a race valve fitted, or you are building up excess crankcase pressure, most probably due to ring failure. Do you know the history of the engine?
Yep all stock there. Maybe it is rings, will investigate next month then but doubt it. It kind off always did this oil to air-box thing. There is always a lot of compression in my crank, even when you turn-over you can feel it/hear it as it tries to move engine and even with throttle open it compresses and struggles to start moving. When it goes it goes.
