A PA36-300 WAS RETURNED TO SVC WITH AN OVERHAULED ENG WHICH HAD PISTON PINS NOT MEETING SPECS IN AN AIRWORTHINESS DIRECTIVE.

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PISTON PIN FAILURE. ENG OIL PRESSURE DECREASED A SMALL AMOUNT. THE PLT LANDED THE ACFT AND CALLED FOR INSPECTION. OIL SCREEN WAS REMOVED AND PIECES OF ALUMINUM WERE FOUND. ENG WAS REMOVED AND DISASSEMBLED. THE PISTON PIN ON #5 HAD BROKEN AND IN TURN; HAD BROKE THE PISTON SKIRT. PIECES OF ALUMINUM HAD STARTED TO CLOG THE OIL PICK-UP SCREEN CAUSING THE DECREASE IN OIL PRESSURE. THE PISTON PIN BROKE BTWN THE PISTON AND THE ROD. DAMAGE TO THE CYLINDER SKIRT AND CASE OCCURRED WHEN THE PISTON SKIRT BROKE AT PISTON PIN HOLE. THE ENG WAS OVERHAULED MAR/XX/97 (TSO: 323.49) WITH ALL NEW CYLINDER KITS (P/N: 05K21120). INSPECTION REVEALED THAT ONLY 1 OUT OF 6 PISTON PINS ADDRESSED IN AIRWORTHINESS DIRECTIVE 97-01-03 WAS SHIPPED FROM LYCOMING (JAN/XX/96). THE ANNUAL INSPECTION WAS COMPLETED ON 3/XU/97. DUE TO MISREADING THE AIRWORTHINESS DIRECTIVE AND THE INVOICE DATE; THE AIRWORTHINESS DIRECTIVE WAS MISSED. I CAME TO THE CONCLUSION THAT FROM THE DATE ON THE INVOICE AND THE DATES ON SVC BULLETIN THAT IT WOULD HAVE BEEN CAUGHT AT LYCOMING. TO PREVENT A RECURRENCE OF THIS OVERSIGHT; NOTHING SHOULD BE TAKEN FOR GRANTED. ENCLOSED IS A PICTURE OF THE FAILED PISTON PIN; CRANK SHAFT AND ROD THAT WERE SENT IN FOR INSPECTION AND FOUND TO BE OK. THE CASE WAS EXCHANGED AND A NEW CYLINDER KIT WAS PURCHASED FROM LYCOMING AND INSPECTED. THE PROB OCCURRED MAY/XX/97 AND THE CAUSE OF THE PROB WAS DISCOVERED AT TEARDOWN ON JUN/XX/97.