As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE ENGINE OIL SCREENS WERE REMOVED AND INSPECTED FOR DEBRIS. THE LEFT ENGINE OIL SCREEN CONTAINED A SNAP RING THAT WAS BROKEN IN THREE PIECES. THE ENGINE WAS REMOVED AND SENT TO ANOTHER REPAIR STATION FOR OVERHAUL. THE STATION REPORTED THAT THE SNAP RING CAME FROM THE END OF THE TACHOMETER SHAFT, WHICH IS CONNECTED TO THE END OF THE CAM AND SITS IN THE ACCESSORY HOUSING. THE SNAP RING BROKE AND MIGRATED OUT OF PLACE AND INTO THE OIL SUMP.