As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE DISASSEMBLED FOR OVERHAUL. CRANKSHAFT CLUSTER GEAR BOLTS (6 EACH) SHEARED. NEW PART NUMBER LARGE GEAR (P/N 656991) AND BOLTS (P/N 656990) WERE IN PLACE IAW LATEST SERVICE BULLETINS. LACK OF FRETTING SIGNATURES ON CRANKSHAFT GEARS AND ATTACHING BOLTS INDICATE THAT THIS WAS A SINGLE OVERLOAD EVENT; LIKELY KICK-BACK DURING STARTING. NOTIFIED OPERATOR TO INSPECT SHOWER OF SPARKS STARTING SYSTEM.