fuel tank patch along skin lap joint

[Browncbr1]

My fuel tank sealant has been holding up for the most part, given the sealant age.   However, I'm guessing a little bit of turbulence has caused a lap seam to start leaking.  This is the one skin seam that goes front to back.   I want to just patch it and while I'm in there, patch a short outboard section of the seam that goes laterally along top of the wing. 

I will be using polygone gel.

Are these lap joints particularly difficult to access and remove sealant?   Should I remove the outboard access panels to access top and bottom seams , or all access panels?    

[Don Heene]

I removed all my access panels, it's easier to scrape and apply Poly Gone.  You will need 2 very thin scrapers to remove the access panels.  Just work it around the panels many times and they will release.  I first used a vacuum with dish soap to find the leaks (there's a thread on this on MS).  Used clear plastic over the panels to see the leaks.  Used Poly Gone to strip.  Give it time to work,  It comes off like snot.  When it dries reapply.  I had to scrape and apply a few times.  It is difficult to remove and takes a long time.  You will need plastic scrapers and plastic brushes.  Used aluminum tape under the wing around the access panel to direct the washed out Poly Gone into the cement trays to catch the water.  Also used a mirror on the bottom to look at the top of the tank inside with a led light inside the tank to apply the Poly Gone and Flamemaster sealant.    I used Flamemaster CS 3204 CLASS B-2 Black for the tank and Flamemaster CS 3330 Class B-2 for the panels.  Going into it knowing it's going to take a long time helps, take your time and do a good job, in the end after doing it I would do it again if needed, it's not hard.   Did this myself, an  A&P signed off after I was done.   That's my 2 cents.

[carusoam]

Nice pics and description, Don!

Great details.

Best regards,

-a-

[Browncbr1]

Thanks Don, noted that all panels need to come off.  I’m thinking just drain tank, remove panels and apply poly gone, then come back the next day to scrap and reapply.     I have plastic razors that do pretty good.    I’m thinking just reseal the entire seam, rather than trying to find where along the seam is leaking.  Thanks!

[N201MKTurbo]

You really need to do the soap bubbles leak test. It is the only way to tell if you have fixed it or not. The leak may not be where you think it is.

I have never used Poly Gone. MEK or Ethanol will soften it enough to remove it with scrapers and brushes. I would save the Poly Gone for a complete reseal.

 

[RLCarter]

Is the leak on the top or bottom of the wing? My limited experience with PolyGone (Gel) is letting it sit over night made little difference. I only had the inboard top inspection panels off of each wing to tweak my new fuel sending units. To install the panels I used 2 rods that I threaded on the ends, after applying the sealant the panel was placed in the tank and the rods were ran through a screw hole in the wing and threaded into the corresponding nut plate in the panel and lifted and held in place while my IA started the screws. If your lap joint is on the bottom be sure not seal up the holes at the bottom of the rib (there is an AD). I had read on here that a piece of Formica with a sharpened edge worked best for scraping the sealant, I had the plastic razor blades along with several other things and found the Formica did work the best. You'll end up making several of these prison shank looking tools, I used a 1" putty knife that I narrowed and rounded off, then the edges were rounded and smoothed so it wouldn't scratch or dig into the aluminum to remove the panels. It's not rocket science but it can be messy so don't let the PolyGone get anywhere you don't want it

[N201MKTurbo]

15 minutes ago, RLCarter said:

Is the leak on the top or bottom of the wing? My limited experience with PolyGone (Gel) is letting it sit over night made little difference. I only had the inboard top inspection panels off of each wing to tweak my new fuel sending units. To install the panels I used 2 rods that I threaded on the ends, after applying the sealant the panel was placed in the tank and the rods were ran through a screw hole in the wing and threaded into the corresponding nut plate in the panel and lifted and held in place while my IA started the screws. If your lap joint is on the bottom be sure not seal up the holes at the bottom of the rib (there is an AD). I had read on here that a piece of Formica with a sharpened edge worked best for scraping the sealant, I had the plastic razor blades along with several other things and found the Formica did work the best. You'll end up making several of these prison shank looking tools, I used a 1" putty knife that I narrowed and rounded off, then the edges were rounded and smoothed so it wouldn't scratch or dig into the aluminum to remove the panels. It's not rocket science but it can be messy so don't let the PolyGone get anywhere you don't want it

For the threaded rods I just went to the Ace Hardware and got the longest 6-32 bolts they had and cut the heads off.

[N201MKTurbo]

I have posted this before, but this is the best tool for removing the panels:

https://aircraft-tool.com/shop/detail.aspx?PRODUCT_ID=SWG7

 

[LOCOLJ]

Once the location of the leak is determined, how much of the old sealant should be removed? clear away a few inches either side? or just the spot?  

[bradp]

5 hours ago, N201MKTurbo said:

I have posted this before, but this is the best tool for removing the panels:

https://aircraft-tool.com/shop/detail.aspx?PRODUCT_ID=SWG7

 

That skin wedge is about the most useful tool in my hangar period. Doesn’t damage anything. 

[N201MKTurbo]

6 hours ago, LOCOLJ said:

Once the location of the leak is determined, how much of the old sealant should be removed? clear away a few inches either side? or just the spot?  

You should clear away a few inches either way. It is actually easier than trying to do a small spot. You may find the old sealant is deteriorating in which case you want to go back till you get to good sealant.

I just got through doing it myself about 1/2 hour ago. Ever sense I got my tanks re-sealed in 2006 it has been a constant cycle of patching. The tanks were much better before the reseal. 

[LOCOLJ]

Thanks for your response N201MKturbo, we are planning a patch project in the next few weeks.