What flywheel are you using? I had the same issue when I switched from a Sirio engine to the Go. I was using a Kyosho flywheel and everything worked the first time I installed it. The next time it bound! I figured out that I needed a collet shim to move the flywheel out a touch because these engines are slightly bigger (very slightly) in diameter. The difference was the extra bit of torque I used on the second time around.