As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAGNETO FAILURE DUE TO ROTATING MAGNETO CAM SHAFT SHEARING OFF JUST BELOW THE CAM, AT THE FORK. THE PROBABLE CAUSE OF THE BREAK IS METAL FATIGUE AT THE FORKED GROOVE WHICH CAUSES CRACKS AND THEN LEADS TO FAILURE. THIS IS THE SECOND MAGNETO THIS SHOP HAS SEEN FAIL THIS WAY AT ABOUT THE SAME TT. (K)