What was found
IN CRUISE FLT, AT 2500 FT AGL & APPROX 15 MILES FROM DESTINATION, PILOT NOTED A SLIGHT VIBRATION ON STARBOARD (RT) ENG FOLLOWED BY A LOUD BANG. IN RESPONSE, PILOT SHUT THE ENG DOWN, AND FEATHERED PROP. AFTER LANDING, THE POST-FLIGHT INSP REVEALED THE NR 3 CYLINDER HEAD PROTRUDING THROUGH THE OTBD MATING JOINT OF THE UPPER AND LOWER ENGINE COWLINGS. WHILE REMOVING LWR COWLING IT BECAME EVIDENT THAT ENTIRE CYLINDER ASSY HAD SEPARATED FROM ENG CASE SHEARING ALL CONNECTING STUDS. NR 3 PISTON CONNECTING ROD END CAP WAS RECOVERED IN THE LWR COWLING WITH BOTH CONNECTING ROD BOLTS INSERTED. OF THE (2) CONNECTING ROD BOLTS (PN LW-13923) ONE (1) WAS INTACT WHILE THE OTHER BOLD HAD BEEN BENT APPROX (90) DEGREES AND SNAPPED IN PROXIMITY TO MATING CONNECTION OF CONNECTING ROD AND END CAP. A CURSORY INSP OF ENG COULD LOCATE THE 2 CONNECTING ROD NUTS (PN LW12186). THREAD DAMAGE TO BOTH BOLTS SUGGESTS BOTH NUTS LOOSENED AND FELL OFF CONNECTING ROD BOLTS AS OPPOSED TO FAILING STRUCTURALLY. NR 3 CONNECTING ROD WAS LOCATED IN THE LWR COWLING AND SUSTAINED DAMAGE FROM STRIKING OPPOSING CYLINDER FLANGE AND ENG CASE (ON ONE END) AND STRIKING THE NR 3 CYLINDER FLANGE (ON THE OTHER END). PISTON WAS RECOVERED IN THE LOWER COWLING. DAMAGE TO PISTON WAS LIMITED TO FAILURE OF BOTH WRIST PIN FITTINGS. BOTH VALVES WERE NORMALLY SEATED AND SHOWED NO EVIDENCE OF STRIKING THE PISTON.