Completed Cover Seal  502 
28-11-0  Figure 820  Nov 15/77 
Page 828 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

(13) Apply prepack and faying surface seals.
(a)  Apply prepack seal.
1)  Apply coat of Class B sealant to one of the parts. Shape sealant with a fairing tool to general contours of cavity. Sufficient sealant must be applied to ensure complete filling of the cavity (Fig. 822).
2) Assemble parts within sealant work life (Fig. 804).
3) Apply corrosion resistant finish (topcoat) (Ref par. 4.D. (15)) as required.

(b)  Apply faying surface sealant.
1)  Apply a coat of Class B sealant to one faying surface with an extrusion gun or a spatula. Spread sealant over entire surface to obtain a uniform coating approximately 1/32 inch thick (Fig. 823).
2) Assemble parts within sealant work life.
3) Fair out extruded sealant to leave a smooth fillet along joint.

NOTE:  Sufficient sealant must be applied to ensure a continuous extrusion on both sides of joint after assembly of faying surfaces.
4) Apply corrosion resistant finish (topcoat) (Ref par. 4.D. (15)) as required.
(14) Raising the seal plane.
(a)  As an option to replacing an injection, prepack, or faying surface seal, the seal plane may be raised (relocated) to isolate the failed seal from fuel. 1) Structure surrounding failed seal must be carefully reviewed to determine the
point to which seal plane must be raised. New seal plane will be established by fillet sealing around structure that surrounds seal and sealing fasteners which pass through structure. Fig. 824 shows a typical repair of a failed seal by raising the seal plane. Raising the seal plane can involve an extensive amount of sealant addition so in many cases structure removal and replacement of failed seal will be the best action.
502 
Nov 15/77  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  28-11-0 Page 829 

Typical Combination of Pre-pack and Fillet Seals  502 
28-11-0  Figure 822  Nov 15/77 
Page 830 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

502  Raising the Seal Plane to Repair a Failed Prepack Seal 
Nov 15/77  Figure 824  28-11-0 
Page 831 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

(15) Apply corrosion resistant finish (topcoating) by brush or spray.
WARNING:  THE AREA IN WHICH CORROSION RESISTANT FINISH (TOPCOATING) IS APPLIED SHOULD BE WELL VENTILATED. DO NOT GET IN EYES OR ON SKIN. WASH HANDS BEFORE EATING. KEEP AWAY FROM IGNITION SOURCES.
NOTE:  Corrosion resistant finish is applied to tank internal structural surfaces, especially bottom and lower sides of tank. It may be applied as a topcoat over surfaces of previously applied sealant which has cured to at least a tack-free condition or it can be applied directly over metal surfaces. Only BMS 10-20 Type II material can be applied before, as well as after, the application of sealant. MIL-C-27725 material can only be used as a top coat finish after any necessary sealant repair is complete.
(a)  
Ensure that all application equipment and fuel tank surfaces to be coated are perfectly clean. If in doubt, clean equipment and tank surfaces with B01013 solvent, Series 93 (Ref AMM/SOPM 20-30-93), solvent immediately prior to finish application.

(b)  
Check that sufficient finish material is available to complete application.

(c) 
 Deleted

(d)  
Mask, as necessary, any non-structural fuel tank equipment areas which are in, or adjacent to, the area which is to receive the finish (topcoating) application.

CAUTION:  REMOVE ALL MASKING TAPE AFTER FINISH APPLICATION IS COMPLETED OR FUEL FEED BOOST PUMP SUCTION INLETS MAY BECOME CLOGGED.
NOTE:  Corrosion resistant finish (topcoating) must not be used on bonding surfaces, clamps, O-ring surfaces, valves, measuring sticks, tank and compensator units, wiring, boost pumps, filler caps, or other non-structural equipment.
(e)  
Ensure that finish application temperature will be maintained at 50-100°F (10.0-37.8°C) with less than 85 percent relative humidity throughout the application process (brush or spray).

(f)  
Apply finish (topcoating) by brush.

502 
28-11-0 Page 832  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/98 

1)  Apply thin film (approximately 0.0005 inch) with soft bristle paintbrush, brush in one direction as much as practicable. a) Avoid fast scrubbing motions or repeated brushing out of wet compound
　
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