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Fuel tank leak in outboard end

Captain Avgas

Well Known Member
A soap film solution check of my left fuel tank has revealed a small leak at the join between the end rib and the rear baffle at the outboard end of the tank. Please see the photo in which I have highlighted the location in red. It's right under the flange of the end Z bracket.

Does anybody have any good ideas on how to repair this leak in this location. Obviously it's at the far end of the tank from the inboard inspection port so no chance of access from that end.

The archives suggest that some builders use green loctite and use a vacuum inside the tank to draw the loctitite into the fissure from the outside. I could try that but I'm thinking I'd like a 'proseal' solution to the problem to ensure longevity.

I could remove some of the universal rivets that fasten the end rib flange to the rear baffle to the z-bracket but I'm concerned that by levering open the gap to get some proseal in there I could do more damage to the seal in adjacent locations.

Tackling it from the inside would mean installing a new access port in the rear baffle....quite lot of work with the possibility of getting swarf inside the tank.


 
I had a similar situation at two locations on one of my baffles. I addressed the situation this way:

I went to the local autoparts store and purchased a hand-vaccuum pump. I scotchbrighted some .016 aluminum pieces to act as shims to spread open the affected area. I next mixed-up some tank-sealant and added acetone to thin it somewhat.

DSCN1786.jpg


I set the thinned sealant aside and applied a small vaccuum to the fuel tank. (I was actually able to use a shopvac at the fuel drain to do this faster than with the handpump alone but I'd advise caution so as not to implode the fuel tank!)

DSCN1792.jpg




With the vaccuum applied, I simply worked the slurry into the affected areas with a shim and allowed the vaccuum to pull the sealant in.

DSCN1789.jpg


I next cleaned-up the area but continued to maintain a small vaccuum on the tank for about a day.

DSCN1790.jpg


After a week, to allow the sealant to fully cure, a pressure test revealed no leak!

In retrospect, I think I should have removed the rivets in that area to allow a greater gap for sealant to infiltrate. After sufficient time for sealant infiltration, I could have clecoed the area to prevent cured sealant from creating a bulge in the affected areas, followed by re-riveting.

I hope my method provides you with some ideas to meet your challenge.

Good luck!
 
This may work

Flamemaster (ProSeal) offers a product that is the same compound in the cartridge that is already thinner than the stock mix from the can. You can prop the tank in an angle that positions the problematic seam to the bottom, get the caulking gun/cartridge and inject the thinned Proseal through the fuel fill openning. Let gravity help you guide the material where you needit. You coulalso use a dowel or similar to manipulate it.
 
More info

Additional information to above post:

Flamemaster: (818) 890-1401

Part number: CS 3204 A 1/2

The product we typically get from Van's is Class B (thicker)

In a discussion with one of the techs at Flamemaster, he indicated this to be a suitable product to flow into seams with already applied Class B product. Same stuff...just thinner.

As always, check with the OEM and Van's to be sure.
 
Another thought, if you use thinner stuff (Flamemaster makes some that's a light syrup consistency), is that it can be drawn up into a 1/4" nylon tube, guided into position through the filler fitting using a coat hanger or other wire taped to the tube, and then forced out of the tube using low pressure air in the exact spot you need it. Injecting it directly at the seam instead of allowing it to 'slosh' greatly reduces the chance that it will come off in sheets, as some of the older sloshing compounds have done in the past.

Charlie
 
Bob,

From memory you have a 7A. I have a 9A and am not familiar with the RV 7A tanks so forgive me if this is a silly suggestion.

On my 9A, if I had a leak in this area I would get access to the inside of the fuel tank through the fuel cap hole and make up a tool using something like a wooden tongue depressor to apply a fresh layer of proseal over the whole area where the rib attaches to the rear baffle.

Fin
9A
VH-FLA
 
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Hi Bob

I've just spent the last week fixing some minor leaks in my tanks including weeping rivets on top of the tanks along the rear baffle line which caused significant paint blisters after I left my 7 in the sun on a hot day with full fuel. I popped the blisters and the larger ones were weeping fuel dye.

I'm not joking when I say i still can't work out why they leaked. My tanks are standard/slow build tanks and I had pro-seal covering all rivet heads and the lap joints.

My theory is that some of my proseal wasn't mixed properly or in the alternative it was a bad batch because when i removed the proseal in a couple of lap joint areas it was a bit gummy rather than elastic.

You know how complex my paint job is so you can understand that it hasn't been my greatest week after attacking my tanks with sand paper. I'm still working on the paint job and it will take another week to complete and tidy up before flying again.

Back to the point - I used A1/2 proseal - its the runny one (rather than B) that goes off in about 30 mins. I put my shop vac on the tank and turned it on before rubbing proseal into the rivet heads and the lap joints where there were some additional minor leaks/weeps. This seams to have fixed the problem in my case.

One of the morals of the story - never fill your tanks to the brim and leave your aircraft in the sun on a hot day.

Good luck with your fix. At least you found it before painting!

Cheers,

Jon.

PS By the way Bob - I would highly recommend covering all the rivet tails and the lap joint associated with the rear baffle with proseal. In your photo they appear unsealed....my tanks are proof that those rivets in the baffle which are outboard of the tank can leak. It is much easier to deal with these issues before you fit your tanks for the last time!
 
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Thanks

Thanks to everyone who offered solutions for my fuel tank leak. I appreciated every suggestion and the effort that everyone went to.

In the end I opted for the most time consuming and difficult strategy of fabricating an access port into the rear of the tank so that I could tackle the problem of repairing the leak from the inside of the tank. See photo of fabrication in process.

I figured that repairing the leak from the inside would result in the most reliable long term solution.

However creating the access port is turning out to be quite a task. The spacing between the outboard end rib and second rib is small and there is not room for a circular port (of useable size)....so it had to be a custom fabricated rectangular port.

To Jon Clements: Thanks for the good advice. And I'm super sorry to hear about the weeping rivets under your exquisite paint job.....what a real bummer. I just hope you don't eventually have the same problem with the rivets in the outboard leading edge tanks as well !!!

 
It is easy to access every bay of the tank for resealing. Access the outboard bay through the end rib with the same cover plate size used for the rear access ports.

2a0b243.jpg


When inside, install filet seals:

t6yr61.jpg

os8qo4.jpg
 
From memory you have a 7A. I have a 9A and am not familiar with the RV 7A tanks so forgive me if this is a silly suggestion.

On my 9A, if I had a leak in this area I would get access to the inside of the fuel tank through the fuel cap hole and make up a tool using something like a wooden tongue depressor to apply a fresh layer of proseal over the whole area where the rib attaches to the rear baffle.

Fin has it right...you should be able to slather on some pro-seal through the filler.
 
It is easy to access every bay of the tank for resealing. Access the outboard bay through the end rib with the same cover plate size used for the rear access ports.


Dan, I've already installed the access port through the rear in that bay (which was a real pain to instal I can tell you). The only advantage of the rectangular port is that I could insert the stiffening ring into the inside of the tank without having to slice the ring.

But if I was going to do it again I'd go through the end rib. Great suggestion Dan....just wish you'd popped up with the wisdom earlier. :)
 
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