The bolt head on the crankshaft bolt is so worn on my TR3A that the crank will not engage enough to spin the engine. The crank tries to work itself out of engagement when torque is applied to the bolt head. The bolt is NLA at the American big three. A used bolt may be worn worse than mine. Is there available somewhere the engineering drawing of the bolt head design so that I may rework the head to the original design or better yet a source unknown to me that has this bolt for sale in original design at a reasonable price. I can guess but I do not want to fix the head so it can easily break my arm if the engine should backfire on cranking.