What was found
DURING AN OIL CHANGE, THE THERMOSTATIC BYPASS VALVE WAS REMOVED FROM INSPECTION PER LYCOMING MANDATORY SB 518A. THE CRIMP NUT ON VALVE WAS FOUND LOOSE AND VALVE SEAT WORN. WHILE INSPECTING A BEECH SPORT, PIPER CHEROKEE 180 AND AN ENSTORM 280F HELICOPTER, IT WAS FOUND THEIR VALVES HAD LOOSE CRIMP NUT AND WORN VALVE SEAT. THE DEFECTIVE VALVES WERE ALL REPLACED WITH SUPERIOR AIR PARTS SL 53E19600 WHICH HAS DRILLED NUT AND ROLL PIN.