As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PERFORMANCE OF MAGNETO "500 HOUR INSPECTION", IMPULSE COUPLING WAS FOUND TO BE CRACKED AT THE TAPER SEAT AND AT BOTH AXLE RIVET LOCATIONS ON BASE PLATE OF IMPULSE COUPLING ASSY. HAVE SEEN A VERY LARGE PERCENTAGE OF IMPULSE COUPLINGS DEVELOPE CRACKS IN SERVICE. CRACKS WERE VISIBLE USING MAGNETIC PARTICLE INSPECTION NDT METHOD. RECOMMEND A MATERIAL/DESIGN CHANGE TO IMPROVE RELIABILITY OF IMPULSE COUPLINGS ON MAGS.