What was found
FLIGHT CREW REPORTED ENGINE SPUTTERED DURING INITIAL CLIMB. UPON INTERNAL VISUAL INSP OF LT MAGNETO, FOUND BROKEN MAGNETO SHAFT BELOW DRIVE GEAR. ALUMINUM MAGNET CASTING FAILED AT STEEL SHAFT MATING JOINT. ROTATION OF STEEL SHAFT IN ALUMINUM CASTING YIELDED EXCESSIVELY RETARDED TIMING. MAGNETO WAS "FACTORY NEW" WITH 235.4 HOURS TT AND HAS NOT BEEN OPENED PRIOR TO THIS EVENT. A REPLACEMENT "FACTORY NEW" MAGNETO OF THE SAME TYPE WAS INSTALLED TO RESOLVE THE PROBLEM. PREVIOUSLY ON 9/9/2008 AT 1112.0 HOURS AIRCRAFT TOTAL TIME, THE RIGHT MAGNETO WAS FOUND TO HAVE FAILED DURING RUN-UP CHECKS WITH THE SAME FAILURE MODE.