57-05-04 PRATT & WHITNEY: Applies to All Wasp Jr. and Military R-985 Series Engines, Except Those Used in Helicopters.
Compliance required at next overhaul.
It has been found that an earlier AD was not effective in preventing crankshaft cracking at the thrust nut threads and possible loss of the propeller in flight as failures of these crankshafts are still occurring. Increased strength afforded the old design crankshaft by the rework on (1) has been determined to be necessary to raise the level of safety of these engines. This rework included the smoothly blended thread roots and a closely controlled undercut depth and the special inspections and shotpeening as required by AD 56-26-03.
At the next overhaul, accomplish either (1) or (2):
1. Except for the new design crankshafts noted in (2), or those marked "14F-56" at the front end between the locking holes for the propeller retaining nut, the crankshaft is to be subjected to a special magnetic inspection procedure, shadowgraph inspection, necessary radius in the thread root, and shotpeening of the thrust bearing nut threaded area. Because of the special equipment and techniques involved, only those activities approved by P&W will be able to accomplish this rework, inspection, and shotpeening. Interested parties should contact Technical Supervisor, Service Department, Pratt & Whitney Aircraft, East Hartford 8, Conn., for approval and detail instructions. Crankshafts reworked in accordance with these special instructions can be identified by the marking 14F-56 on the front end near the propeller retaining nut locking holes.
2. New design crankshafts which can be identified by P/N 261278, 261279, or 264164 on the front end near the propeller retaining nut locking holes may be installed. These crankshafts incorporate roll hardened threads and these threads should not be reworked.
NOTE: - In the event of oil leakage in the front section of the engine during any operation, immediately conduct thefollowing inspection:
(1) Remove the propeller, thrust nut cover, nut, slinger and spacer.
(2) Carefully clean the area to be inspected.
(3) Using a dye penetrant and a 6- to 10-power optical glass, check for the presence of cracks. If any crack is found, the crankshaft must be replaced.
(P&W Service Bulletin No. 1488, dated October 10, 1956, covers this subject.)
This supersedes AD 56-26-03.