As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE PILOT REPORTED THAT THE ENGINE BEGAN RUNNING ROUGH IN FLIGHT. THE AIRPLANE WAS TAKEN TO THE SHOP FOR INSP AND THE TECH FOUND THE NR 4 EXHAUST VALVE TAPPET FACE AND THE NR 2 INTAKE TAPPET FACE WERE MAKING METAL. THE ENGINE WAS REMOVED FROM THE ACFT FOR REPAIRS.