This is what you need to do. Take out the engine mount screws and put some loctite on them and screw them almost all the way on. Then take a sheet of paper and fold it in half and put it between the spur gear and bell gear and press it together tight. Then tighten down the screws on the engine mount. Then take a unfolded sheet of paper and put it between the gears. It should put deep creases in teh paper but not rip it. Let the loctite dry and you are ready to run...