As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CYLINDER FAILED COMPRESSION CHECK DUE TO EXHAUST VALVE LEAKAGE. VISUAL INSPECTION REVEALED BURNED EXHAUST VALVE WITH NO SIGNS OF OVER TEMP OR CARBON BUILD UP. VALVE STEM AND GUIDE WORN BEYOND SERVICE LIMITS. EXHAUST VALVES IN CYLINDERS 4 AND 5 EXPERIENCE IDENTICAL FAILURES AT 247 HOURS TOTAL TIME. PROBABLE CAUSE IS POOR QUALITY CONTROL AT ENGINE BUILD RESULTING IN POOR ALIGNMENT BETWEEN VALVE GUIDE AND SEAT.(K)