Hi guys, I hope someone can help me out here. I have a US 41cc gasoline engine mounted to the new GP Aeromaster bipe. The engine has a spring starter and is brand new(old stock). I purchased it from a member here on RCU a couple years ago. My question is why is there so much runout on the crankshaft and if this is common on these engines. I can hold the prop in the 12-6 o'clock postion and move the top of the prop at least 1/64"-1/32" back while pressing on the top blade with my hand. I do know that it starts very easily and runs great with no adjustments to the carb whatsoever. I have also noticed that it seems to run very smooth until 3/4 throttle, then the plane shook so badly it loosened the 4-40 socket head cap screws holding the N struts in place to the point that I lost 4 of them along with the lock washers and flat washers for the N struts. By the way this engine is hard mounted to the firewall. I appreciate any help someone can give me. Thanks, Ben