Sounds like the starter gear or bendix gear. I have a 46 it did the same thing. The gear that engages the fly wheel on the starter. It has a free wheeling function and that part wears out. My starter spun but did not turn the engine. Thats the only part it can be. When I turned my by hand it felt ok but when there is a load on it would just spin. Its a sealed unit. Replaced it and it works great now.
