As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN)IN CRUISE FLIGHT #4 ENGINE BEGAN TO RUN ROUGH ACCOMPANIED BY BACKFIRING THROUGH THE INDUCTION SYSTEM. THE ENGINE WAS SHUTDOWN. POST FLIGHT INSPECTION DISCLOSED THE #8 CYLINDER INTAKE VALVE SEAT HAD CA ME ADRIFT, PREVENTING THE INTAKE VALVE FROM CLOSING.