What was found
DURING PRE-TAKEOFF ENG RUN-UP, IT WAS NOTED THAT THERE WAS SOME ENGINE ROUGHNESS. THE MAG CHECK INDICATED THE THE LT MAGNETO WAS NOT FIRING PROPERLY (THE ENG WAS QUITTING). THE MAGNETO WAS REMOVED AND OPENED FOR INSP. THE DISTRIBUTOR GEAR WAS FOUND TO BE MISSING APPROX 10 TEETH IN SUCCESSION AND ANOTHER MISSING ABOUT AN INCH AWAY. THIS CAUSED THE MAGNETO TO BECOME UNTIMED IT ITSELF AND NOT FIRE PROPERLY. THE LOGBOOK INSP REVEALED THAT THE 500-HOUR MAGNETO INSP HAD BEEN COMPLIED WITH AT THE CORRECT INTERVALS. THERE IS NO INDICATION WHAT CAUSED THE TEETH TO FAIL.