What was found
PILOT REPORT OF HEARING A BANG AT STARTUP. WHILE BRINGING THE PLANE TO THE MAINTENANCE SHOP ACROSS THE AIRFIELD, THE PILOT HEARD A LOUD GRINDING NOISE COMING FROM THE LH ENGINE, HE THEN SHUT THE ENGINE DOWN. IT WAS DISCOVERED DURING VISUAL INSPECTION THAT THE RH MAGNETO ON THE LH ENGINE HAD THE IMPULSE COUPLING FAIL. THE RIVETS HOLDING THE PAWLS HAD BECOME LOOSE AND THEN DEPARTED THE MAGNETO, TRAPPING THE PAWLS UNDER THE IMPULSE COUPLING, BINDING THE MAGNETO DRIVE IN SUCH A WAY AS IT WOULDN'T TURN. THE CRANKSHAFT IDLER GEAR HAD EATEN THROUGH 2 OF THE TEETH ON THE MAGNETO DRIVE GEAR. PIECES OF THE DRIVE GEAR, IMPULSE COUPLING SPRING, RIVETS, STOP PIN, AND PAWL WERE FOUND IN THE ACCESSORY CASE AND OIL SUMP. THE MAGNETO DID NOT DEPART THE AFT END OF THE ENGINE.