As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ROUGH ENGINE, LEFT MAG DEAD ON RUN-UP. REMOVED LEFT MAG AND FOUND SHOULDERED MAGNETO DRIVESHAFT BUSHING WITH SHOULDER MISSING. UPON EXAMINATION OF BUSHING, DETERMINED IT WAS THE OLD STYLE, SINTERED IRON PN 10-51659. IT SHOULD HAVE HAD A MACHINED STEEL BUSHING PN 10-163049 INSTALLED. REF: TCM SB 556C OR AD 74-26-09.