My friend's 912 won't burp until after maybe 60 blades. Compression is what pushes the oil from the crankcase to the oil tank. His plane is a nose dragger and the tank is about 1 to 2 inches higher than mine (KF7 conventional). The engine is older but low time. The compression feels weak compared to mine. Concerns would be: How do you know the true oil quantity? He bought the aircraft second hand and has never done a compression/leak down test. I thought that would be a great place to start. Any thoughts appreciated.