As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE CRANKSHAFT THRU BOLT APPEARS TO HAVE FRACTURED IN THE AREA JUST BELOW THE THREADS IN THE NECKED DOWN AREA. THE HEAD OF THE COTTER PIN THAT SAFETY LOCKS THE BOLT WAS FOUND IN THE OIL SUMP. THE ENGINE WAS THEN REMOVED AND DISASSEMBLED. UNKNOWN PROBABLE CAUSE, OTHER THAN POSSIBLE FATIGUE FAILURE AND RESULTED IN FRACTURE OF THE CRANKSHAFT IN THE MATING SPLINES.