As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A ROUTINE INSPECTION, A COMPRESSION TEST WAS PERFORMED. CYLINDER NR 1 DID NOT HOLD PRESSURE AND A LOUD HISSING WAS HEARD FROM THE VICINITY OF CYLINDER HEAD. CYLINDER WAS REMOVED AND A SMALL HOLE WAS OBSERVED IN CYLINDER HEAD BETWEEN FINS, THE HOLE WAS NOT VISIBLE WHEN INSTALLED ON ENGINE BECAUSE OF HOLES LOCATION IMMEDIATELY ADJACENT TO THE NR 3 CYLINDER HEAD. NO ROUGHNESS OR POWER LOSS WAS REPORTED WHEN AIRCRAFT WAS GROUND RUN PRIOR TO INSPECTION.