S 818-231

 (4)  
To find the leak source, do this task: Fuel Tank Leak Detection (AMM 28-11-00/601).

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747-400 MAINTENANCE MANUAL
 F. Remove the Damaged Sealant
 S 158-232
 (1)  
To remove a bad fillet seal do these steps:

 (a)  
Use the sealant cutting tools (Fig. 801) to remove the bad sealant.

 (b)  
To cut sealant away from a fillet seal, refer to (Fig. 803). 1) Cut the ends of the bad sealant at a slope such that the

 new sealant makes an overlap with the remaining sealant. 2) Make sure you cut the sealant smoothly.

 (c)  
If the fillet seal bond is good, it is not necessary to cut the sealant to the bare metal (Fig. 803). 1) Make sure you remove all sealant that is loose.

 S 158-233
 (2)
To remove a fillet seal that includes fasteners do these steps:

 (a)  
Cut around the bottom of the fastener with a sealant cutting tool (Fig. 803).

 (b)  
Use a pliers and pull the sealant from the fastener.

 NOTE: It is not necessary to remove small quantities of the
____ sealant that bond to the fastener.
 S 158-234
 (3)  
To remove a bad injection seal, do these steps:

 (a)  
Remove the bad sealant from short injection channels with hooked wire and small cutting tools.

 NOTE: You must disassemble long injection channels
____ (SRM 57-00-00). You can repair bad injection seals if you raise the new seal plane above the old seal plane to isolate the bad seal from the fuel.
 (b)  Make sure the injection channel is clean.
 NOTE: If air is caught in the injection channel, new
____ sealant cannot fully fill the channel.
 (c)  Be careful not to cause damage to the tank structure.
 S 158-235
 (4)
To remove a bad prepack or faying surface seal, do these steps:

 (a)  
Disassemble the structure around the bad sealant (SRM 57-00-00).

 (b)  
If you do not want to disassemble the structure, you can repair the leak if you raise the new seal plane above the old seal plane to isolate the bad sealant from the fuel.

 NOTE: The area of bad sealant must be small.
____
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747-400 MAINTENANCE MANUAL
 (c)  Remove the bad sealant with cutting tools and scrapers.
 S 158-236
 (5)  
If there is topcoat on the surface of the sealant, do these steps:

 (a)  
Remove all the topcoat from the sealant repair area unless you know the topcoat is a coating of BMS 10-20, Type II, or BMS 1-20, Type II finish material.

 (b)  
Use abrasive paper to remove the used topcoat until either bare metal or sealant shows (in good condition).

 WARNING: DO NOT GET SOLVENTS IN YOUR MOUTH, OR YOUR EYES, OR ON
_______ YOUR SKIN. DO NOT BREATHER THE FUMES FROM SOLVENTS. SOLVENTS ARE HAZARDOUS MATERIALS. SOLVENTS MAY BE FLAMMABLE OR HARMFUL TO THE ENVIRONMENT. REFEFR TO PRODUCT MATERIAL SAFETY DATA SHEETS (MSDS) AND LOCAL REQUIREMENTS FOR PROPER HANDLING PROCEDURES.
 (c)  
Use clean gauze pads soaked with Series 93 solvent (AMM 20-30-93/201), to clean all surfaces and sealant in the repair area.

 (d)  
Use a clean gauze pad until the area is dry.

 (e)  
Continue to clean and dry the surfaces until the dry gauze pad stays clean.

 S 158-237
 (6)  
If there is precoat sealant in the repair area, do these steps:

 (a)  
Remove all used sealant precoat from the repair area unless it is known that the precoat is BMS 5-26 Type II or BMS 5-45 sealant, in good condition.

 WARNING: DO NOT GET SOLVENTS IN YOUR MOUTH, OR YOUR EYES, OR ON
　
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