You may have sheared the flywheel key.

The crankshaft could be bent.

The piston connecting rod may have broke.

I got my chipper shredder started and used it today. However that was after two multi hour work sessions.

As I said I was chipping up a cyprus branch when I over feed it, and the motor died. Apparently there was one of he long small branch attached to the branch and it wrapped itself around the driven shaft, creating a "brake" that stopped the engine. That is why it would not turn. the "brake" was set.

I worked about 5 hours the other day, trying to get to the stick that was wrapped around the drive shaft. I could not get the flywheel of so had to poke at it with a long screw driver that I had sharpened to a mini chisel. It finally came free but I was too tired to put the chipper back together.

This morning I reassembled the chipper, and put all the screws and parts back into the unit. However there were many false starts when I would get some assembly done, find it was wrong, and have to disassemble, correct the error, and reassemble.

I finally got it back together, It started right up. I went out and chipped up a bushel of mulch, I then put it away, saving the remainder of the pile for another day.