What was found
(CAN) DURING CLIMB-OUT, THE NR 1 ENGINE BEGAN TO RUN ROUGH. A SHORT TIME LATER, OIL STARTED TO APPEAR ON THE ENGINE COWLING. THE CREW DID A PRECAUTIONARY SHUTDOWN AND RETURNED TO THE POINT OF DEPARTURE. POST-FLIGHT INSPECTION FOUND THE NR 3 CYLINDER WITH A CRACKED HEAD, MOVEMENT OF THE HEAD ALLOWED THE PUSHROD SEALS TO UNSEAT RESULTING IN THE OIL LEAK. THE NR 3 CYLINDER WAS REPLACED AND GROUND RUN SERVICEABLE.