As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOT REPORTED RT ENGINE RUNNING ROUGH ON GROUND. MX CARRIED OUT COMPRESSION CHECK AND DETERMINED NR 4 CYLINDER "0" COMPRESSION. CYLINDER REMOVED AND FOUND THE EXHAUST VALVE SEAT LOOSE, TRAPPED UNDER VALVE AND VALVE EDGE BROKEN OFF, CYLINDER HEAD BURNED. VALVE CONTACTED PISTON HEAD.