AD 52-03-01

52-03-01 RANGER: Applies to All 6-440-C Series Engine Models. To be accomplished as indicated. To preclude the failure of cast pistons, the following inspections and modifications should be accomplished at engine overhaul or when installing new or replacement pistons. 1. Inspection. (a) Inspect pistons by the fluorescent penetrant inspection method, or an equivalent, for cracks especially in areas around the piston pin boss and on the reinforcing web inside the piston. If cracks are found in these locations, the piston should be discarded. (b) Inspect pistons to ascertain if a 3/32-inch radius has been added at the inner ends of the ID of the piston pin bosses. Pistons which do not incorporate this radius should be modified as shown in Figure 1 in order to relieve stress concentrations. Pistons with cracks in this location which cannot be removed by the following modification should be discarded also.

2. Modification. After thoroughly cleaning the piston, place it head down on the bench; insert cutter No. AT-390, or an equivalent, between the piston pin bosses, facing in the direction of the boss to be cut. Insert handle No. AT-391, or an equivalent, through the opposite boss and engage with cutter. Cut radius by rotating cutter in a clockwise direction until the outer end of the 3/32-inch radius blends into the surface at the end of the piston pin boss. Repeat this procedure for the opposite piston pin boss. Blending tools No. AT-390 and AT-391 are no longer available from the engine manufacturer. (Drawings for these tools may be obtained from Fairchild Engine and Airplane Corp., Farmingdale, Long Island, N.Y.)