As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE EXHAUST VALVE SEAT WAS FOUND TO HAVE COME OUT FOLLOWING THE ENGINE TEST STAND RUN AND PRIOR TO THE INITIAL INSTALLATION RUN ON THE AIRCRAFT. A 'RATTLE' WAS NOTED AS THE ENGINE WAS TURNED THROUGH BY HAND. THE CYLINDER OVERHAUL SHOP HAS BEEN ALERTED AND OTHER CYLINDERS OF THE SAME BATCH CHECKED. THE CYLINDER WAS MACHINED TO ACCEPT A P-20 SEAT, BUT A P-10 WAS INSTALLED.