jon, I used to end all my rides with a wrecked flywheel woodruff key, and if yours moved it could have fired while the piston was still moving up, bending your rod. The cure? simple, cheap, and it never moved afterwards.get some valve grinding paste(being careful to keep it away from seals if crank in engine) and put some on taper using coarse paste first, then fine paste, and spin flywheel back and forth for about 5 minutes each type of paste which matches flywheel to crank taper.IT WILL NOT MOVE AGAIN.The present woodruff key is over 3 yrs old and no more dnf's as it were.Result.K.