TM-9-2815-200-35 Maintenance Manual for AVDS-1790-2M AVDS-1790-2A and AVDS-1790-2AM Engines Download
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necessary and check for broken welds, loose rivets or weld nuts. If parts are cracked or torn, they must be repaired or replaced. Check shroud seals for hardness, tears, or other damage. Mark damaged seals for replacement if the part is otherwise serviceable. 6-4. Repair a. General. Most engine parts and com- ponents may be repaired as outlined below. After repair, clean all parts thoroughly to prevent metal chips from repair operations, or abrasives used in repair operations, from entering working parts of the engine. b. General Repair of Castings. (1) Replace all castings when cracks have penetrated high stress areas such as fillets or webbing. (2) Replace all castings which do not conform to tolerances specified in the ap- propriate repair and rebuild standards table. (3) Replace all castings on which machined surfaces are burred or nicked to the point of impairing subsequent assembly or operation. Repair minor damage to machined surfaces with a fine mill file or crocus cloth dipped in dry- cleaning solvent or mineral spirits paint thinner. (4) Replace all castings having flanges which are severely warped and cannot be repaired to provide a proper seating surface with its mating part. Repair minor warpage of mounting flanges and mounting pads by working surface across a sheet of crocus cloth held tightly on a surface plate or similar flat surface. (5) Repair damaged pipe threads in tapped holes with a used tap. Note. Pipe plug threads in castings must be in good condition to prevent oil leakage. c. Welding of Aluminum Alloy Castings. Note. The following procedures (1) through (7) are based on the applicable paragraphs in Specification MIL-W-8604 and MIL-W-45205, and outline the requirements, equipment, and welding process used for the repair of aluminum alloy castings. Specific information relating to the welding of individual castings will be covered in the appropriate section of this chapter. (1) Operator. Welding shall be performed by welding operators who have successfully met the requirements of Specification MIL-T-5021, for Material Group IV (Aluminum Alloys). Operational: TM 9-237 (Nov. 1967). The base material covered in this procedure is Type 355- T71 Federal Specification QQ-A-601. (2) Equipment. An alternating current arc welding machine shall be used for heliarc welding. Class 4043, conforming to Specification QQ-R-566a or MIL-E-16053 welding rod, is compatible with the base material and shall be used for all welding repairs in this material group. All equipment shall be consistent with good standard welding practices, and be ac- ceptable to the Government Inspector. (3) Processes. (a) MIG (Metal Inert Gas) process. The MIG process is recommended when welding aluminum plate greater than 1/8 inch thickness. (b) TIG (Tungsten Inert Gas) process. When welding aluminum plate 1/8 inch thick and under, the TIG process is recommended. (4) Casting preparation. (a) Cleaning. All foreign material must be removed from the area to be welded prior to repair operations. The area shall be cleaned using a stainless steel wire brush, drill, burring tool, or approved chemical process, whichever is applicable. (b) Cracks. Determine flow of cracks by using dye check method. Drill stop holes at crack ends with a 1 / 4-inch drill and mill out cracks to provide a “V” aperture. (c) Fractures. Check area around the fracture for cracks using dye check. Drill stop holes at the ends of detected cracks with a 1/4- inch drill and mill out crack to provide a “V” aperture. (d) Missing metal. If the size of the damaged area permits, mill out and chamfer that area to 30 degrees to provide a 60 degree in- cluded angle. The insert piece required for this area must be identical in composition and may be cut from scrapped castings or suitable sheet stock. Fit insert piece into milled area, so that 1/6- to 1/8-inch is maintained between insert and casting wall. (5) Preparation for welding. Precisely measure castings at appropriate locations to detect dimensional changes caused by welding repair. Record dimensions for checking after repair has been made to be sure that critical dimensions have been held. (6) Preheat prior to welding. Preheat 6-5