As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER LEVEL OFF FOR CRUISE, A VIBRATION OR BUFFET WAS NOTED. ALL ENGINE TEMPS AND INDICATIONS APPEARED NORMAL. WAS UNABLE TO IDENTIFY WHICH ENGINE WAS CAUSING VIBRATION/BUFFET. RETURNED TO AIRPORT AND FLIGHT WAS TERMINATED. POST FLIGHT ENGINE RUN-UP REVEALED A BAD MAG ON THE LT ENGINE DURING MAG CHECKS. OPENED MAG AND FOUND BROKEN DISTRIBUTOR GEAR. DISTRIBUTOR GEAR WAS REPLACED WITH NEW PART. QUILL SHAFT IN ENGINE GEAR BOX WAS SENT OUT FOR MAGNAFLUX INSPECTION TO VERIFY NO DAMAGE DURING ENGINE VIBRATION. POST FLIGHT GROUND CHECKS VERIFIED OPS NORMAL AND ACFT WAS RETURNED TO SERVICE.