As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CONTINENTAL (AIRBOSS) CYLINDER P/N 658598 S/N AC15FA427 INSTALLED ON AUGUST 31, 2015 PER THE ENGINE LOG BOOK. COMPRESSION TEST IN JULY 2020 IDENTIFIED LOW COMPRESSION ON THIS CYLINDER, WITH A LEAK IN THE EXHAUST VALVE. THE EXHAUST VALVE WAS REMOVED AND THE VALVE SEAT FOUND TO BE MISALIGNED. MECHANIC BELIEVES THIS TO BE A MANUFACTURING DEFECT IN THE CYLINDER ASSEMBLY. PART WAS REPLACED WITH A NEW SUPERIOR MILLENNIUM CYLINDER ASSEMBLY.