As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
COMPLAINT OF AN INTERMITTENT ENGINE VIBRATION. SUSPECTED AN IGNITION SYSTEM PROBLEM. FOUND 1 MAGNETO HAD JUMPED INTERNAL TIMING DUE TO DISTRIBUTOR BLOCK BEARING COMING LOOSE FROM THE BLOCK. OPENED THE SECOND MAGNETO, FOUND VIRTUALLY IDENTICAL DEFECT BUT IT HAD NOT JUMPED TIMING YET. THE BEARING HOLDS THE DISTRIBUTOR GEAR IN PLACE AGAINST THE MAGNETO SHAFT DRIVE GEAR. IN THIS LOOSE CONDITION, THE GEARS MAY DISENGAGE AND THE MAGNETO INTERNAL TIMING IS LOST.