What was found
DURING A PHASE 2 INSPECTION, CYLINDER NR 5 WAS FOUND TO HAVE LOW COMPRESSION (10/80) WITH A STRONG LEAK PASSED THE EXHAUST VALVE. SUBSEQUENT INSPECTION FOLLOWING THE INSTRUCTIONS FOUND IN LYCOMING SB 388C REVEALED THAT THE EXHAUST VALVE WAS PARTIALLY STUCK AND WOULD NOT FULLY CLOSE. THE EXHAUST VALVE ALSO COULD NOT BE REMOVED FROM THE CYLINDER ONCE THE CYLINDER WAS REMOVED FROM THE ENGINE. LYCOMING RECOMMENDS THE FOLLOWING INTERVAL FOR INSPECTING NON-HELICOPTER ENGINES, "400 HOUR INTERVALS OR EARLIER IF VALVE STICKING IS SUSPECTED UNTIL EXHAUST VALVE GUIDES ARE REPLACED WITH GUIDES MADE OF IMPROVED MATERIAL (REFER TO LATEST REVISION OF SERVICE INSTRUCTION 1485)".