As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ALTERNATOR PULLEY COOLING FINS BECAME DETACHED FROM PULLEY CAUSING ALTERNATOR TO VIBRATE OFF ENGINE SHEARING BRACKET BOLTS. INSTALLED NEW BOLTS AND ALTERNATOR. PROBLEM HAS NOT RECURRED. POSSIBLE CAUSE IS FATIGUE OF COOLING FINS. SUGGEST INSPECTION OF FINS EACH 100 HOURS FOR CRACKS.