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Fuel Tank Rivets Seeping Fuel

Jim Kranich

I'm New Here
I've been flying my RV-7A for a year now and have just noticed about 10 rivets in the fuel tank are seeping fuel, causing a bubble in the paint around the rivet head. Most of the problem rivets are on the top side of the tank and a few on the bottom. Has anyone experienced this and if so, what's the best fix?

Jim
 
I had a row of 10 rivets seeping fuel on the bottom of one tank and a couple on the top of the other. Both were along the baffle at the rear of the tank. I bit the bullet, pulled the tanks, opened them up and applied sealant to the inside of the tank. Vans sells a kit to accomplish this. Leak test on the bench before reinstallation.
 
If you do a deep-dive search on the forums here you'll find a lot of old posts on this subject. There is no firm concensus on what causes it, but there does seem to be a trend pointing to builders who used MEK to clean up the proseal on the exterior rivet lines before the proseal had firmly set, and some of those rivets subsequently leaking fuel. Nothing definitive, but enough anecdotal evidence to suspect there is a grain of truth in that route.
 
Running mogas?

I had this happen many years ago on a '68 Cardinal when I started running mogas (long before ethanol was required) I've been reluctant to run mogas in my RV-3 for fear of the same.
Prick one of the bubbles and see if any fuel comes out. I never got a drop out on the Cardinal and could flatten the bubbles out so they were hardly noticeable. Nearly all of the bubbling rivets were on top of the wing.
 
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Thanks for the info. I might have to pull the tanks. I'm trying to find a method that doesn't require that. Do you know if anyone has had success with just applying tank seal on the exterior head of the rivet?
 
My left tank leaked at the outboard end. I used some spare parts from the build to install an access panel (same as on the inboard end). Drill a hole large enough for an air nibbler to make the opening. As mentioned above, Vans sells a repair patch too, but it is less sturdy and is a one-time install using blind, sealed pop rivets. With the access panel, it is much easier to remove again if the seal isn't perfect the first time.
 
Can't speak for consensus, but the statistics are clear. Paint blisters over tank rivets has nothing to do with MEK application. Nor is it strictly a QB tank problem.

Jim, roughly speaking, when were your QB tanks assembled?

BTW, it is not difficult or risky to install access ports in the rear bulkhead.

P8080003.JPG


Closed%20End%20Rivets.JPG


P1220002.JPG
 
Interesting joggle around the edges of those cover plates Dan. Advantages of doing this?

The polysulfide sealant specification includes a basic minimum test elongation of 200%. The standard is as low as 75% when tested in adverse conditions.

Let's use 200%, and assume a no-joggle riveted overlap joint with a 0.001" sealant thickness. Apply a shear load. If the strain displaces the two components by more than 0.002", the sealant line is subject to adhesive or cohesive failure.

Increasing the thickness of the sealant line in the fay surface boosts the capacity for displacement...so just add an outboard joggle.

Joggle%20Seal.jpg


BTW, warm fuel is one of the adverse conditions. And most readers will be surprised to learn there is no polysulfide standard for resistance to avgas. The test fluid is AMS2629: https://www.sae.org/standards/content/ams2629/

The good news is that most sealant batches test at 300% or more. The joggle is easy insurance.
 
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Hmmm, I should see if I could work a slight joggle into the tank rear baffle panel top & bottom flanges. Those joints need all the help they can get.
 
RV3 hubcaps

Can't speak for consensus, but the statistics are clear. Paint blisters over tank rivets has nothing to do with MEK application. Nor is it strictly a QB tank problem.

Jim, roughly speaking, when were your QB tanks assembled?

BTW, it is not difficult or risky to install access ports in the rear bulkhead.

P8080003.JPG


Closed%20End%20Rivets.JPG


P1220002.JPG

I read on here that if you use the RV3 hubcaps as access hole covers, you will get more capacity when it is all said and done. YMMV
 
I had 1 weeping rivet on my tanks. I purchased the kit with the tanks 1/2 done so I don?t know if it was my rivet or the last owners rivet that leaked. In any case I took a small plastic syringe, cut off the tip about 1/8 inch long and put some new pro seal in it. I cut a 1/4 inch piece of 3/8 fuel line (vinyl). Place the fuel line over the cleaned weeping rivet and place the syringe over that. Squeeze the down on the syringe plunger as hard as you can. The fuel line will bulge out and you can squeeze pro seal in. Carefully wipe clean and do the next one. Simple and no tank removal needed. I was lucky to do mine to an unpainted fuel tank.
No further leaks:)
 
Not leaks

I don't think the paint bubbles over the rivets are leaks as much as some kind of out gassing from the proseal.

My RV-3B quickbuild wings have them too. Using 87 octane gas station gas (up to 10% ethanol).

I forget the survey results -- but how long after tank completion was the airplane painted? Mine at least a year.

Would be interesting to hear from someone who left their plane out in the weather (sun and cold) for years before they painted it.

Or perhaps the proseal never fully cures.

Finn
 
I have had several leaker rivits on my -7 fuel tanks. The ones with just blisters on the top side of the tank, I ignore.

The seepers on the bottom, i have had success drilling out the rivit and putting a sealed 3/16 pulled rivit buttered well with proseal in its place.
 
I don't think the paint bubbles over the rivets are leaks as much as some kind of out gassing from the proseal.

My RV-3B quickbuild wings have them too. Using 87 octane gas station gas (up to 10% ethanol).

I forget the survey results -- but how long after tank completion was the airplane painted? Mine at least a year.

Would be interesting to hear from someone who left their plane out in the weather (sun and cold) for years before they painted it.

Or perhaps the proseal never fully cures.

Finn

I have had multiple paint bubble over the rivet on both RV and none of them have leaked.
 
I too have several paint blisters on the upper rivets of my quick build RV-7, and in fact am working on the "fix" now utilizing the vacuum-Locktite method. I placed two layers of blue tape on left and right side of the repair area to create a screed for applying JB Weld Marine epoxy as a filler as added leak protection. I'm now in the process of sanding to level the filler prior to painting.

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https://previews.dropbox.com/p/thum...fwAGGHJv6eQ9O/p.jpeg?size=256x256&size_mode=2
 
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Hi, leaking fuel tank rivets can be due to not washing the rivets before using them on the tanks. The rivets as supplied are OILY. It appears that in manufacturing the rivets oil is used as a lubricant. This can lead to the rivets leaking fuel.
If you put a couple of hundred in a small class jar and add enough solvent such as acetone then shake it for a while then remove the rivets and compare the solvent with a clean jar of solvent, it will be discoloured by the oil from the rivets.
If you need more convincing, mix some sealant and make a thick layer on a flat surface, poke some cleaned longish rivets into the sealant so the head is still clear of the sealant and do the same with some unwashed rivets. Let the sealant set and try pulling the rivets out of the sealant. You will find the unwashed rivets will pull out easily but the cleaned rivets won?t.
I?d suggest cleaning the rivets at least twice with fresh solvent before use.
I am surprised Van?s have never included this in thereinstructions.
 
I concur with the above advice. Clean those rivets thoroughly. I soaked all of my tank rivets in MEK before using them (let them dry obviously before setting). No leaks after 6 years.
 
Excellent method for penetration . .

I had 1 weeping rivet on my tanks. I took a small plastic syringe, cut off the tip about 1/8 inch long and put some new pro seal in it. I cut a 1/4 inch piece of 3/8 fuel line (vinyl). Place the fuel line over the cleaned weeping rivet and place the syringe over that. Squeeze the down on the syringe plunger as hard as you can. The fuel line will bulge out and you can squeeze pro seal in. Carefully wipe clean and do the next one. Simple and no tank removal needed. I was lucky to do mine to an unpainted fuel tank.
No further leaks:)

You can pick your sealant, but this is the best (technically) method to ensure the sealant penetrates any gap around a rivet, the pressure is at least 200X what can be developed with any in-tank vacuum.
 
Timely thread, good info, as the drain flange on my left tank is leaking. I hoped I had taken care of it by using the syringe method on the exterior, and recoating the shop heads on the interior, since a build error left gave me an extra fuel cap on the inboard edge of the tank to give me access. But, it failed the leak test this morning. So I guess a full R&R of the flange is next. I am not sure there is room and geometry to get a bucking bar in through the extra fuel cap. Does anyone know of a countersunk closed-end blind rivet to replace the AN426AD3-4's used for the flange?
 
More information requested

I had 1 weeping rivet on my tanks. I purchased the kit with the tanks 1/2 done so I don?t know if it was my rivet or the last owners rivet that leaked. In any case I took a small plastic syringe, cut off the tip about 1/8 inch long and put some new pro seal in it. I cut a 1/4 inch piece of 3/8 fuel line (vinyl). Place the fuel line over the cleaned weeping rivet and place the syringe over that. Squeeze the down on the syringe plunger as hard as you can. The fuel line will bulge out and you can squeeze pro seal in. Carefully wipe clean and do the next one. Simple and no tank removal needed. I was lucky to do mine to an unpainted fuel tank.
No further leaks:)

This is good information. I too have several rivets weeping on the underside of the left tank. I?m considering this procedure but I?m a little hesitant as I?m not the builder and have never used pro seal.

Do you have a picture of the syringe and fuel line applicator? Do I need to mix the pro seal, or does it come in a package ready to use?How long after squeezing the plunger do you wait to wipe the excess around the rivet? Does the tank need to be empty? How long should you wait before filling the tank? Can you use this method on a painted aircraft? If so, what are things to watch for and to be aware of?

I appreciate any information.
Thanks,
Pat Moran
(619) 994-3542
 
I had a 601P Aerostar years ago. Those that have owned one well know of the propensity to get fuel leaks. I was told to use a Click Patch to solve the problem. Used to carry some on board with me. was told that is what the airlines use. Used them more than once and they worked.
 
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