It was running fine and while in the midst of cutting, it died and when trying to restart, it would just click. I initially thought starter, so I rebuilt and it is working fine when benchtested. I moved over to the solenoid and replaced as I had a new one to begin with. Tested batter as well, battery is good. Still only clicked when I tried to start. I turned by hand unti it froze then attempted to crank. It fired up the made a sound that sounded like someone dropping a socket into an engine, then died. Since then, it will crank but only spin, does not fire up and I can spin it with one hand and hardly any tension. Please help...

1) Flywheel key is sheared. Replace.
2) Adjust valves
3) Worried about possible internal damage such as broken rod or bent valves. After doing 1 & 2 crank engine with plug removed, manually first.

Initial problem probably valves. Starter was probably OK.