What was found
IMPULSE COUPLING FAILED ON SLICK 4373 MAGNETO. MAGNETO HAD 230 HOURS AND 123 START CYCLES SINCE 500 HOUR IRAN. TOTAL TIME ON MAGNETO 765 HOURS. IMPULSE COUPLING WAS REPLACED WITH NEW M3529 SLICK IMPULSE COUPLING AT TIME OF IRAN DUE TO EXCESSIVE WEAR ON EXISTING COUPLING. DISASSEMBLY OF THE COUPLING AFTER FAILURE SHOWED EXCESSIVE WEAR (HOLES HOGGED OUT) IN RETENTION PLATE, ONE RIVET FAILED IN SHEAR, SECOND RIVET WAS CLOSE TO THE SAME FAILURE. PAWL ARM AND SHEARED RIVET DROPPED INTO ACCESSORY CASE. CASE OF MAGNETO DESTROYED DURING FAILURE.