As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING CRUISE, THE FLIGHT CREW HEARD THE NR1 ENGINE BACKFIRE. THE ENGINE WAS SHUTDOWN AND THE PROPELLER FEATHERED. DURING INVESTIGATION, THE MAINT CREW DISCOVERED THE EXHAUST VALVE IN CYL NR 9 HAD DROPPED INTO THE CYL. SOME PIECES OF THE VALVE WENT OUT THE EXHAUST PIPE. THE CYL WAS REPLACED, ENG GROUND RUN AND THE MAIN OIL SCREEN WAS INSPECTED. THE ACFT WAS RETURNED TO SERVICE.