C. Procedure
S 288-200
(1) The surfaces are prepared incorrectly.
(a) The surfaces must not contain these unwanted materials: 1) Grease 2) Metal particles
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3) Hair
4) Loose paint
5) Wax
6) Other unwanted materials.
(b) These unwanted materials can cause the sealant not to bond correctly.
S 288-239
(2) The sealants are mixed or kept incorrectly.
(a) Make sure you mix the correct quantities of the base material and the accelerator material.
NOTE: Sealants have two parts that you must mix together,
____ the base material and the accelerator material. Synthetic rubber makes the base for most sealants. The manufacturer adds materials to control the strength and cure time. The manufacturer also adds materials to make the sealant more flexible and to increase the time you can keep it. These materials also make the sealant more resistant to fuel.
1) Obey the instructions from the manufacturer when you mix the sealant. 2) If you do not obey the instructions, you can change the properties of the mixture. 3) This can cause a bad seal and fuel tank leakage.
(b) Sealants have a specified shelf life.
1) After the specified time, you must do a test of the sealant materials to see if you can use them.
NOTE: Refer to the task, "Keep and Mix the Sealant
____
Correctly".
(c) You can keep some sealants in a cooler (refrigerator) for a short time after they are mixed with the accelerator material. 1) You must discard these sealants after the specified time.
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S 288-201
(3) The sealants are applied incorrectly.
(a) Fuel leaks can occur if you do not do these steps: 1) Obey all of the manufacturer's instructions. 2) It is a good procedure to use a brush to apply the precoat. 3) Do all the necessary steps to apply the sealant. 4) Make sure there are no air bubbles in the sealant. 5) Make sure you fully fill all of the spaces with sealant. 6) Make sure you do not make an overlap with the sealants. 7) Make sure the sealant touches all of the surfaces. 8) Make sure you permit the sealant to dry for sufficient cure
time before you put fuel in the tank.
NOTE:____Four hours is a recommended minimum. Refer to the task, "Let the Sealant Dry (Cure) Correctly".
S 288-202
(4) The fasteners are loose.
(a) Loose fasteners can start fuel leaks because they permit the attached surfaces to move. 1) Mating surface seals get cracks and cause leakage through
the seal plane. 2) Loose rivets do not seal again unless you repair them. 3) Sealant or metal seal covers do not bond with loose
fasteners.
S 288-203
(5) Fittings and connections are installed incorrectly.
(a)
Fittings and connections attached to the fuel tank structure are sealed with O-rings.
(b)
Fittings and connections that go through the fuel tank structure are also sealed with O-rings.
(c)
Damaged or incorrectly installed O-rings can cause fuel leaks.
TASK 28-11-00-398-204
4. Sealant Preparation and Curing______________________________
A. General
(1)
It is very important to keep and to mix the sealants and the corrosion resistant finish correctly. You must obey the approved procedures to prevent damage to equipment and injury to persons.
(2)
Obey the manufacturer's instructions to fully mix all of the components.
(3)
Do not mix sealants that you apply with a brush until you use them.
(4)
Do not put thinners in the sealant.
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