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Dean Pichon

Well Known Member
During the annual condition inspection of my -4, I drained the starboard tank in preparation for calibration of the EI fuel gage I had recently installed. The tank had been empty for about a week before I filled it in 4 gallon increments during the calibration process. Within minutes after filling the tank, I noticed a major puddle forming under the aircraft. I was able to quickly identify the source of the leak to be the access plate on the root rib of the tank. I surmised the leak was due to the fact that the cork gasket had dried out during the past week.

When I built the tanks about 15 years ago, I used the cork gaskets supplied with the kit and a Permatex brand gasket material that was popular at the time. This morning, I pulled the tank, removed the access panel and cleaned the faying surfaces in preparation for re-sealing. (After sacrificing 16 gallons of av gas...) I have attached a few photos for reference.

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The rotten gasket after 14 years of flying

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The root rib after cleaning

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The access panel after cleaning

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The wing minus its tank


I don't plan on using cork or Permatex again, but would like recommendations from others who have built tanks more recently than me. My default solution will be to use polysulfide, but I am a little concerned about how difficult it may be to remove the access plate should future maintenance be required. If there are more enlightened strategies, I would appreciated the input. Interestingly, the old access plate was quite easy to remove. Even more interesting was the fact that avgas worked well as a solvent to remove the Permatex residue...

Thanks in advance for the help.

Dean
 
Dean Pichon said:
During the annual condition inspection of my -4, I drained the starboard tank in preparation for calibration of the EI fuel gage I had recently installed. The tank had been empty for about a week before I filled it in 4 gallon increments during the calibration process. Within minutes after filling the tank, I noticed a major puddle forming under the aircraft. I was able to quickly identify the source of the leak to be the access plate on the root rib of the tank. I surmised the leak was due to the fact that the cork gasket had dried out during the past week.

When I built the tanks about 15 years ago, I used the cork gaskets supplied with the kit and a Permatex brand gasket material that was popular at the time. This morning, I pulled the tank, removed the access panel and cleaned the faying surfaces in preparation for re-sealing. (After sacrificing 16 gallons of av gas...) I have attached a few photos for reference


I don't plan on using cork or Permatex again, but would like recommendations from others who have built tanks more recently than me. My default solution will be to use polysulfide, but I am a little concerned about how difficult it may be to remove the access plate should future maintenance be required. If there are more enlightened strategies, I would appreciated the input. Interestingly, the old access plate was quite easy to remove. Even more interesting was the fact that avgas worked well as a solvent to remove the Permatex residue...

Thanks in advance for the help.

Dean
Click to expand...

I used pro seal thickly applied then snugged the screws down, but not too tight, leaving a 1/16 or so layer. This created it's own gasket as well as sealing the cover plate. After a couple of days I tightened the screws to their final tightness, after a year of flying all looks great still
 
Tank access cover reseal

I've had excellent results with using tank sealant without gaskets, luckily I always have some leftovers from prior jobs kicking around.
Roughen up mating surfaces with scotch rite pad, than degrease both (don't forget to remove that tape on your tank second rib). Apply a 3/16" bead of pro seal around bolt circle of both tank & cover, spread out maintaining a higher ridge along the bolt circle. Put the cover in place, using new clean screws, dab the threads in a bit of pro seal before inserting it in the holes than torque down fully. You should end up with about a 1/8" ring of excess sealant all around the cover, I just leave it there. There should also be a little ring of sealant squeezed out around each screw head.
If you ever have to lift that cover off in the future... Apply a heat gun to the spot you gently pry up with a chisel, than work your way around. Cleanup isn't as hard as imagined.
..Also, while the lid is off- have you performed the Vans SB's?
 
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