As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED LT MAGNETO FAULTY DURING RUN-UP. INVESTIAGTION REVEALED HOLE IN MAGNETO ADAPTER PLATE, WITH ALUMINUM SHAVINGS IN ENGINE COMPARTMENT. REMOVED ENGINE FROM ACFT, AND REMOVED SUMP AND ACCESSORY CASE. FUND DAMAGED LT MAGNETO DRIVE GEAR, LT CRANKSHAFT IDLER GEAR, AND BROKEN IMPULSE COUPLING. FOUND COUPLING RETAINER NUT FINGER LOOSE WITH COTTER PIN IN PLACE. IMPULSE COUPLING NOT COVERED BY AD 49-04-04 IN THIS APPLICATION. THE 500 HR INSP WAS NOT DONE. RECOMMEND INSP OF IMPULSE COUPLING AT 500 INTERVAL AS RECOMMENDED BY MASTER SERVICE MANUAL.