As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
OWNER COMPLAINED OF A ROUGH RUNNING ENGINE. DIAGNOSIS FOUND THE BEARING CAP ASSEMBLY MOUNTING SCREWS HAS COME LOOSE ON THE RH MAGNETO.ONE SCREW AND RETAINER HAS FALLEN COMPLETELY OUT. THE BEARING CAP ASSEMBLY WAS FREELY ROTATING 5-10 DEGREES ALLOWING THE MAGNETO TIMING TO CHANGE--CAUSING ENGINE STUMBLING AND ROUGHNESS.