As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FOREIGN OBJECT DAMAGE WITHIN LEFT ENGINE ASSEMBLY CAUSED IDLER GEAR SUPPORT PIN BETWEEN MAGNETO DRIVES TO SHEAR CAUSING MOUNT STUDS TO BREAK AND THE GEAR IT RIDES ON TO ROTATE AND BECOME UNMESHED. IT AFFECTED MAGNETO TIMING AND CAUSED ENGINE TO LOSE POWER AND START RUNNING ROUGH.