What was found
(CAN) DURING AN ENGINE START, AN UNUSUAL NOISE WAS HEARD COMING FROM THE ENGINE. INVESTIGATION BY MAINTENANCE PERSONNEL REVEALED THAT THE LT MAGNETO HAD FAILED AND THAT IT'S IMPULSE COUPLING HAD COME APART. THE PARTS MISSING FROM THE IMPULSE COUPLING ENTERED INTO THE ENGINE AND CAUSED CONSIDERABLE DAMAGE TO THE MAGNETO AND ENGINE. THE ENGINE HAD TO BE REPLACED AS A RESULT OF THE DAMAGE AND RESULTING OIL SYSTEM CONTAMINATION. THE FAILED IMPULSE COUPLING HAD 882.0 HOURS TIME SINCE NEW. NO DEFECTS WERE NOTED DURING THE LAST 500 HOUR INTERNAL INSPECTION (SLICK SB 2-80C) COMPLETED 389.7 HOURS PREVIOUS TO FAILURE.