56-03-02: Derichment Valve Cover

56-03-02 PRATT & WHITNEY: Applies to All Double Wasp CA and CB, and Military R-2800-34, -52W, -57, -73, -77, -83, and -101 Series Engines Using Water Injection. Compliance required as indicated. As a result of engine fires reported due to fuel leakage of the derichment valve cover of PR58 carburetors, the following must be accomplished to reduce the possibility of the derichment valve cover loosening with subsequent fuel leakage: A. At each scheduled inspection which requires the engine cowl to be opened (approximately 100-hour intervals), inspect for fuel leakage while subjected to boost pump pressure. If leakage is noted, either retorque derichment valve cover screws to stop leakage as outlined in B, or replace derichment valve diaphragm as outlined in C. This leakage inspection may be made at alternate scheduled inspections which require the engine cowl to be opened (approximately 200-hour intervals) provided four locating screws with a shank to act as dowelsare installed to eliminate lateral movement of the derichment valve cover. B. The first time leakage is noted it is permissible to retighten the derichment valve cover screws to 20 to 30 inch-pounds torque. If this retorquing corrects the leakage, it will be satisfactory to continue to use the subject diaphragm. NOTE: This retightening can be accomplished only once on a leaking diaphragm. C. At overhaul and whenever a derichment valve diaphragm is replaced: 1. The derichment valve diaphragm holding surfaces of the derichment valve body and diaphragm cover should be lapped to assure that they are flat and to roughen their surfaces. This lapped surface roughness will aid in holding the diaphragm by minimizing cold flow of the diaphragm rubber. 2. The derichment valve diaphragm and the surfaces which clamp it should be dry when the parts are assembled and in particular should be free of oil. 3. During assembly of the parts, the derichment valve cover screws should be tightened to a torque of 20 to 30 inch-pounds. After a period of at least 20 minutes the screws should be retightened to the same torque value. CAUTION: Do not loosen the screws before retightening. P&W Alert Bulletin No. 43 also covers this subject.) When the two new dowel pins described in Bendix Aircraft Carburetor Service Bulletin No. 816 (Advance) or equivalent are accomplished, the inspections in part A. will no longer be required. (P&W Service Bulletin No. 1625 also covers this subject.)