<strong>TO</strong> <strong>35</strong>-1-3 3.8.3.3 When repairs are made on equipment or accessories and/or components are installed or structures are reinstalled, the attaching or faying surfaces shall be protected by sealing all metal-to-metal and composite to metal contact surfaces. All permanent structures shall be installed with faying surfaces wet with MIL-PRF-81733, Type I or IV, Class 1 or 2, Grade A sealant. All removable structure such as access doors, inspection plates, floor panels and plates, and other removable panels (components requiring frequent removal for maintenance requirements) shall either be installed with faying surfaces wet 3-4.2 Change 9
<strong>TO</strong> <strong>35</strong>-1-3 with AMS 3367, Class A or B or PR-1773, Class B sealant or Av-DEC TM HT39<strong>35</strong>-7 or HT3000FR sealant tape in the joints as specified by the system specific maintenance manual. In addition to faying surface sealing, fillet seal all interior seams and all exterior seams (those exposed to the outside environment) that would allow water intrusion using MIL-PRF- 81733, Type II, Class 1 or 2, Grade A sealant. NOTE The following does not apply to parts that are lubricated in the joint areas immediately before or after installation, or to close tolerance bolts and parts that are removed frequently for maintenance requirements. 3.8.3.3.1 Attaching parts, such as nuts (standard, speed, and self-locking), bushings, spacers, washers, screws (standard and self-tapping), sleeves for shake-proof fastener studs, clamps, bolts, etc., do not need to be painted in detail except when dissimilar metal or wood contact is involved with the materials being joined or exposure to a corrosive interior environment or the exterior environment will occur in service. However, all parts shall be installed wet with sealant. For permanent installations, use MIL-PRF-81733, Type I or IV, Class 1 or 2, Grade A sealant and coat the entire mating surface of the parts. For removable installations, use SAE AMS 3367, Class A or PR-1773, Class B sealant and coat only the lower side of the heads of screws and bolts with sealant. For removable installations, do not coat the threads and shanks of screws and bolts or the holes into which they are inserted because this will make future removal almost impossible without damaging the parts. As an alternate for removable installations, the shanks, threads, and lower side of the heads of standard screws and bolts may be coated with MIL-PRF-63460, MIL- PRF-16173, Class II, Grade 3 before they are installed. Close tolerance bolts and parts shall be coated with corrosion inhibiting, solid film lubricant. Use MIL-L-23398 or MIL-PRF- 46147 (air curing type) on aluminum parts and on all types of metallic parts. The solid film lubricant shall be applied and completely cured prior to assembly. Bolts shall be coated on shanks and threads only. A thin bead of sealant shall be applied under the bolt head to impart a wet seal. 3.8.3.3.2 All rivets shall be installed wet with MIL-PRF- 81733, Type I or IV, Class 1 or 2, Grade A sealant. In fuel contact areas, the exposed rivet head and approximately 1/4- inch of the adjacent structure shall be brush over coated with SAE AMS-S-8802 Class A sealant. 3.8.3.3.3 All machine screws, countersunk fasteners, bolts (head end) and nuts which are used in contact with magnesium shall be installed with 5056 aluminum alloy washers. These parts, including the washers, shall be installed wet with MIL- PRF-81733, Type II, Class 1, Grade A sealant and shall be completely fillet sealed with the same material after installation. 3.8.3.3.4 Adjustable parts, such as tie rod ends and turnbuckles shall be installed as follows: (1) If possible, surfaces and threads shall be lubricated and protected before assembly with a film of MIL-L-23398 or MIL-PRF-46147 (air curing type) corrosion inhibiting, solid film lubricant which shall be completely cured prior to assembly. After installation, apply a thin coating of MIL-PRF-63460; MIL-PRF-16173, Class II, Grade 3; or MIL-PRF-81309, Type II, water displacing, corrosion preventive compound (CPC), to all surfaces of these parts. (2) If solid film lubricants cannot be applied, use a thin coating of MIL-PRF-63460; MIL-PRF-16173, Class II, Grade 3; or MIL- PRF-81309, Type II water displacing, corrosion preventive compound (CPC) after assembly. 3.8.3.3.5 When practical, slip fit parts shall be assembled with mating surfaces wet with MIL-PRF-81733, Type I or IV, Class 1 or 2, Grade A sealant. If this process is not practical, coat the interior diameter (ID) of the holes in the receiving part, which is normally the larger structure with a corrosion inhibiting, solid film lubricant conforming to MIL-L-23398 or MIL-PRF-46147 (air curing types) and the outer diameter (OD) of the mating part with one conforming to MIL-L-23398 or MIL-PRF-46147 (air curing types). The solid film lubricant shall be applied and completely cured prior to assembly. 3.8.3.3.6 All cut edges and holes drilled or reworked for bolts, screws, rivets, studs, and bushings of aluminum alloy structures or parts shall receive a chemical conversion coating treatment prior to the installation of the fasteners or bushings and prior to installing or refinishing the structure or parts. Apply a conversion coating to aluminum surfaces, using Touch-N-Prep pen containing Alodine TM 1132. On steel surfaces use the appropriate primer to coat the cut edges of holes prior to reinstallation of the parts. 3.8.3.4 Sealant may be applied by brush, spatula, or caulking gun application. 3.8.3.5 To prevent sealant from contacting adjacent areas during application and smoothout, outline the areas being sealed with masking tape (AMS-T-21595, Type I) so that each tape strip is 1/8 to 1/4 inch from the edge of the seams. 3.8.3.5.1 Apply the sealant between tapes with a nonmetallic spatula or spreader, brush or caulking gun. Avoid the entrapment of air. Work sealant into recesses by sliding the edge of the spatula firmly back over the recesses. Smoothing will be easier if the nonmetallic spatula is first dipped in water. 3.8.3.5.2 Remove masking tape after the sealant has been applied and before it begins to set. Cure time will depend upon the application life of the materials used. 3-5
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