What was found
(CAN) DURING STRAIGHT AND LEVEL CRUISE FLIGHT, THE PILOT NOTICED A SUDDEN INCREASE IN VIBRATION, THOUGHT TO BE COMING FROM THE ENGINE, AND AN INCREASE IN MANIFOLD PRESSURE. HE OPTED TO TURN AROUND AND LAND AT A NEARBY CAMP. DURING HIS DESCENT, THE VIBRATION STOPPED AND ENGINE PERFORMANCE RETURNED TO NORMAL. A COMPRESSION CHECK WAS FOUND NORMAL ON ALL CYLINDERS. A WIGGLE CHECK ON THE EXHAUST VALVES WAS FOUND SATISFACTORY, HOWEVER, 1 OF THE VALVES WAS AT 0.014 WHILE ALL THE OTHERS WERE AT 0.020 OR BETTER. IT IS SUSPECTED THAT THIS EXHAUST VALVE BECAME STUCK AND THEN CAME FREE AGAIN.