As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT MAGNETO IMPULSE COUPLING FAILED. . AD 99-04-04 APPLIES TO THIS MAGNETO ENGINE COMBINATION. INTERVAL FOR REPETITIVE INSPECTIONS IS 250 HRS. MAGNETO HAD BEEN RECENTLY REPLACED WITH A REBUILT UNIT AND HAS A NEW IMPULSE COUPLING. THE IMPULSE COUPLING SHEARED INTERNAL RIVETS CAUSING MAGNETO TO BIND WHICH CAUSED TWO TEETH TO BREAK OFF OF THE DRIVE GEAR AND DAMAGED ACCESSORIES DRIVE SYSTEM.