Fixing tank seam leak from inside - cleaning?

[bluskydreamin]

I'm fixing a small leak on lower tank seam at mid point of rear baffle on a -7. I have the baffle opened up with hole and using vans tank fix cover plate.

What is a good method for cleaning the old leaking proseal area prior to resealing with fresh? One of my concerns is the lead residue from the fuel.

Thanks.

 

[Mike S]

Welcome to VAF!

Jeff, first off, welcome to VAF

I would do my best to scrape the sealant off, and stay away from solvents as much as possible.

If you use something to soften/dissolve the sealant in the problem area, there is a chance you could also unknowingly damage the sealant in good areas.

Also, be sure you actually have the inside source of the leak identified -------fuel can creep along a fair distance to find its way out of the tank.

 

[DanH]

Per the Flamemaster Application Guide, appropriate cleaning solvents are:

1. Isopropyl Alcohol TT-I-735 E
2. Methyl Ethyl Ketone (MEK) ASTM D740 E
3. Naphtha TT-N-95 E
4. Solvent Cleaning Compound MIL-C-38736 E

AIR4069a specifies the MIL 38736.

The much older Essex Chemical Polysulfide Sealant for Aerospace suggests MIL-C-28736 solvent cleaner (a mixture of 50% aromatic naphtha (cont. 30 parts Toluene), 20% ethyl acetate, 20% methyl ethyl ketone and 10% isopropyl alcohol)

All the guides seem to recommend cutting out any sort of questionable fillet seal and starting over. AIR4069a suggests a brush coat of Class A sealant following by a standard Class B fillet.

 

[RVbySDI]

I would also add that you thoroughly wipe down all areas where you used chemicals with cheesecloth after it dries. Once wiped with cheesecloth try not to touch the area with your bare hands. Residual chemical residue or oils from your skin could potentially allow for failure of the sealant to adequately adhere to the aluminum.

Not sure what you are referring to concerning the lead from the fuel. If you are concerned about the health implications of coming into contact with lead, well, I would say you run a higher risk of bad things happening when coming into contact with the chemicals you use more so than any lead residue. That contact will be just as harmful when breathing in the fumes as it will in having it come into contact with the skin. To combat both problems most definitely use gloves and mask/respirator.