What was found
CYLINDER NR 4 EXHAUST VALVE STUCK OPEN ON TAKEOFF. AIRCRAFT RETURNED TO AIRPORT, MADE SAFE LANDING. UPON INSPECTION, CYLINDER NR 4 EXHAUST ROTATER CAP WAS FOUND IN THE BOTTOM OF THE ROCKER BOX. INSPECTED VALVE PER LYC SB 388B. CLEARANCE FOUND TO BE SATISFACTORY. REMOVED CYLINDER FOR INSPECTION AT OVERHAUL FACILITY. GUIDE WAS REAMED, SEAT WAS GROUND. REINSTALLED CYLINDER ASSY. SUBMITTER STATED POSSIBLE CAUSE: CARBON LEAD DEPOSITS STUCK VALVE OPEN.