As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSTALLED 4 NEW CYLINDERS ON OVERHAULED ENGINE. COMPRESSION LOSS STARTED AT ABOUT 300 HOURS THROUGH RINGS AND EXHAUST VALVE SEAT. PULLED CYLINDERS, FOUND BADLY HEATED EXHAUST STEM AND EXHAUST SEAT. EXHAUST VALVES ERODED AND BADLY PITTED. INSTALLED ADDITIONAL 4 NEW CYLINDERS ON 1-20-97 APPRXOIMATELY ONE MONTH AND 50 HOURS AND SAME PROBLEM. OIL TEMP OK AND BAFFLES INSTALLED. SUBMITTER STATED EXHAUST VALVE FAILURE IMMINENT.