i checked my air filter yesterday to discover oil in the air box of 04 raptor 660. looking deeper in to the problem discover the oil is coming from the crankcase breather hose it is spitting alot of oil into the air box
tried to cap it of the hose started to expand like a balloon
a friend told me to check the valves and make sure the are compressed right
i dont think it is the rings becuase i have no smoke

any thoughts will help

 

has no one had this problem

 

Assuming you didnt overfill the sump....its a symptom of blow by. You can do a compression test, and a leak down test to figure out whats wrong.
If the valves were staying open....like youre thinking, it would run really crappy, and compression would be very low...to the point it wouldnt start. My guess, is its coming thru the rings.