Dont want to be a downer but you might have a cracked crank shaft. I couldn't keep mine tight on the new engine. Ended up having a cracked crank. I didn't want to believe what some were telling me but i took the crank out and had it tested. Didn't want to loose my entire 636ci engine due to someone lying about the crank being checked. Better safe than sorry. I acted safe and probably saved my engine from turning into a BOMB!