What was found
AFTER DETERMINING WHAT MAY HAVE CAUSED SN 11513P TO CRACK, WE CHECKED WHICH WAS UNDERGOING MAINTENANCE. WE FOUND SN 11527P TO HAVE A 1" LONG CRACK IN THE SAME PLACE. THIS CRACK STARTED AT THE TOP OF THE FORWARD TT PIN HOLE. THE CRACK LOOKS LIKE IT PROPAGATED FROM A TOOLING MARK. THIS PART HAD AD 86-17-02 PARA "E", "PERFORM A DYE PENETRANT INSPECTION, OR FAA-APPROVED EQUIVALENT, OF THE BOLT HOLE AND ADJACENT MILLED SURFACES. FOR THIS INSPECTION, REMOVE THE NUT, WASHER, AND PIN." A VISIBLE PENETRANT WAS USED TO PERFORM THIS INSPECTION AND NO DEFECTS WERE NOTED. AN INSPECTION WAS REPEATED 9/10/2015 USING FLUORESCENT PENETRANT AND THE CRACK APPEARED. 16 NEW FAA/PMA MAIN ROTOR FORKS BOUGHT FROM MFG WERE PULLED FROM STOCK AND VISUALLY INSPECTED THE SURFACE FINISH OF THE INTERIOR BORE. NONE OF THE 15 PARTS HAD A SURFACE FINISH THAT MATCHED THE BLUEPRINT WE HAVE ON FILE THAT WAS DRAWN ORIGINALLY IN 1947 BY MFG AND REVISED 3/25/1964. THE PRINT SHOWS SURFACE FINISH OF 32. THE NEW PARTS RANGED FROM 125 TO GREATER THAN 500.