What was found
DURING CRUISE CLIMBOUT, AT APPROX F.L. 14,000: PILOT REPORTED LOUD BANG SOUND FROM RT ENGINE, FELT ACFT YAW AND ENGINE INSTRUMENTS INDICATED THAT ENGINE WAS LOSING POWER, PILOT FEATHERED PROP AND SHUTDOWN ENGINE. ACFT RETURNED TO DEPARTURE AND LANDED WITHOUT INCIDENT. INSP OF ENGINE REVEALED THAT THE NR 4 CYLINDER CONNECTING ROD HAD BROKE AWAY FROM CRANKSHAFT AND WAS PRETRUDING FROM LT SIDE OF CASE HALF CAUSING 2.5 " DIAMETER HOLE.