What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Failed tank repair

ccsmith51

Well Known Member
:OK, here is my saga, pull up a chair and an adult beverage.

I purchased my plane in March 2011. There were no tank leaks at the time of purchase. Towards the end of June fuel started showing up at the lower inboard joint of the left tank. In short time it was dripping about a drop a second.

My friend and I pulled the tank, and removed the fuel sender and access plate. We cleaned up that bay by using an air grinder to clean the edges of the proseal, find fresh metal, wipe good with MEK, then put on fresh Van's Flamemaster.

We let it sit for a couple of days, put gas in it overnight, it didn't leak. We then flew to Colorado from North FL, and the day after arriving there, the tank was leaking again, although very little. No dripping fuel, just staining in the same area.

When we got back from our west trip, I drained the tank and went to NC for four months without the plane. When I got back I started on a tank repair.

I removed the tank, removed the fuel sender and access plate, and cut four large holes in the back of the tank, and made four covers:

avsw93.jpg


Inside the tank I cleaned the edges of the proseal, cleaned to bare metal, cleaned with MEK, then applied flamemaster. I did this on the ribs and back panel, all joints. I used a bright light and flexible mirror to see that I had fresh flamemaster over the old proseal.

I installed the covers and sealed them, as well as the end plates:

jgoz11.jpg


I let the tank sit for a week to cure. I put a couple of gallons of fuel in on a Saturday and let it sit overnight. Sunday morning I went and there was a small stain around the lower left back rivet. I shot T&G's for 20 minutes, then filled the tank and went home.

Yesterday after work I went to check on the plane. I was very disappointed to find leaks stains around two of the lower mounting screws, and stains again at the lower inside corner.

So, I'm looking for options. I don't have the tools or experience to build a tank. Coming up with $1,200 - $1,500 for Evan to build me a tank right now is not in the budget.

Is it possible to purchase a tank from a wrecked or parted out RV-4? If so, how would I find one?

If I opened everything up again, and this time using Polygon and chisels and putty knifes and an air grinder and scotchbrite to remove as much of the existing proseal as possible, would I have a better chance of no leaks?

Any other suggestions?

The problem with leaks is that where they appear can be in a completely different location from where they start...

Thanks very much for any insight and assistance.

Chris
 
Chris,

It has to be a frustrating issue to deal with. The bottom line is the fuel tank is leaking because of one or more failure points hidden somewhere in the proseal. As you have found out, pinpointing the source(s) of leaks can be easier said than done.

I am struck by the rather large rectangular holes cut into the back of the tank. Normally, fuel tank access holes are somewhat smaller and round. In your case and in and of itself, that may or may not be an issue but that is a lot of surface area to cover with proseal and it seems with only 5 screws across and 4 down on each cover, an excessively generous fastener spacing exists. The spacing seems so great if it were my plane, I'd be inclined to add a fastener between each existing hole. Do not fall into the common trap of overtorquing the screws. All that does is squeeze out too much proseal and results in leaving a too thin boundary for the proseal to do its job adequately.

33uekc0.jpg


The good news it that without question, the fuel tank is quite repairable. If you do decide to reopen the tank and since the extra large rectangular holes are already cut, take advantage of that by paying extra special attention to the seal dam that runs the length of the fuel tank along the top and bottom of the rear baffle inside the fuel tank. Defects anywhere along that seal dam have been known to cause many a fuel tank leak.

Good luck.
 
Last edited:
Hi Rick,

Thanks for the support and suggestions. I made the access holes as large as I did so that I could get as much access to the interior as possible, and get my die grinder inside with the wire wheel and scotchbrite pads.

The panels are attached with 1/8" sealed rivets. I put a generous layer of flamemaster on the tank, then riveted on the panels, then applied flamemaster on the outside over the edges and the rivets. I have not pulled the tank to see if any of the panels are leaking, but I would be surprised if they are.

I paid particular attention to the seal at the bottom of the tank along the rear baffle. I cleaned it well, and used a bight light and inspection mirror to ensure that I got flamemaster in a continuous film with no breaks.

What I did not do the first time was try to remove all the existing proseal. I figured if I cleaned to bare metal on each side of the existing proseal, and then covered it with a new layer, I would be fine.

Either that idea is flawed, or my execution was lacking, or there is a leak somewhere that I did not address in the repair.
 
Last edited:
If you open this tank again to fix leaks, perhaps you could clean the access panels and install them on the INSIDE of the tank so that the weight of the fuel pushes them into the baffle instead of away from the baffle. Since the panels are rectangular I don't think it'd be difficult to get them inside. You could use a piece of duct tape as a temporary handle while you secure the access plate....

Good luck!
 
When you re-install the plates you should consider using them as "plugs" and install them on the inside. This will force them outward as you add fuel and help keep them sealed.

Looks like I'm to slow in the typing department Fred....
 
Last edited:
Either that idea is flawed, or my execution was lacking, or there is a leak somewhere that I did not address in the repair.

Bingo! When repairing a tank the first step is to identify where the leak is coming from. There's a lot of information on the list on how to go about this. Once the leak is found then a plan can be made and executed.

Otherwise your stabbing in the dark. While it seems logical that resealing the complete tank should fix it, logic failed and you missed the leak, or your work caused a new one.

Identify the source of the leak and then go after it.
 
Thanks for the input, Gary. I really thought I had identified multiple leaks. Before starting the major surgery I removed the tank, placed it on my bench, put a few gallons of gas in it, and left it overnight.

The next morning I found stains at a number of the lower mounting screw holes and the inboard lower corner. The stains at the screws indicated to me that there was a leak(s) along the back baffle seam.

Since the location of the stain did not necessarily mean that was the location of the actual proseal breach, I elected to open the tank completely and attempt to reseal that whole area.

For all I know the leak is somewhere unrelated, and those particular locations are simply where the leak path ends. With that said, I'm not sure how to accurately determine where the proseal breach is...
 
Unfortunately, testing with fuel will not always pinpoint a leak. Fuel "runs" to a low point. The best way to pinpoint a leak is by pressure testing with a soapy solution. Where you see the bubbles is where the tank is leaking.
Be careful about how much pressure you use. You will need no more pressure than you can supply with your mouth. Put a balloon on one port, blow it up through another port, and soap up the seams.
 
With those 4 big access plates cut into the rear of the tank there is a substantial amount of surface area that can fail. I think you should at least try what others have mentioned regarding installing the access plates from the inside. If that fails, (even if it doesn't fail) I would rebuild/replace the tank. To save money, buy the parts and have a local experienced RV builder help you build it. I am sure your local EAA 1379 chapter has connections with someone who can help you. Most RV builders would be happy to help out. Fix it correctly and you will be much happier/safer. If you shortcut repairs to save money you're settling for a less than acceptable standard and possibly inviting disaster. OH, and what Mel said. Use soapy water, not fuel.
 
Last edited:
Thanks, Mel, that is the next plan of attack. However, won't air follow the same path that fuel would? I mean, if there is a proseal breach in the second bay, and the path to the outside is in the fourth bay, how would air help identify the internal proseal breach?
 
We used to use negative pressure testing on really stuborn leaks, just climb in the tank, pump it down, and apply soapy water :D

Pin-pointing the leaking area sounds easy, but that's the hardest part of fixing the leak.
 
shooting blind on your repair...

you really MUST find the leak before attempting to repair it... seal it up and pressurize the tank slightly, Van's sells a fitting adapter for the drain, then make use of kids bubble solution (the sort you make big bubbles with) in a spray bottle and closely spray and examine every rivet and seam on the pressurized tank. Any escaping air will make convenient bubbles. After you have identified the sources of leaking address the area.
 
With those 4 big access plates cut into the rear of the tank there is a substantial amount of surface area that can fail. I think you should at least try what others have mentioned regarding installing the access plates from the inside. If that fails, (even if it doesn't fail) I would rebuild/replace the tank. To save money, buy the parts and have a local experienced RV builder help you build it. I am sure your local EAA 1379 chapter has connections with someone who can help you. Most RV builders would be happy to help out. Fix it correctly and you will be much happier/safer. If you shortcut repairs to save money you're settling for a less than acceptable standard and possibly inviting disaster. OH, and what Mel said. Use soapy water, not fuel.
I have had to deal with leaks on both of my fuel tanks. The most recent was just this past December when I had to pull off the left tank and repair a leak. I have been there. It is a hassle at times to deal with but really not that bad when everything is said and done. However, you have already made one attempt at repairs and in the process cut some pretty large additional holes in your tank. I would be careful about going much further with opening and closing these holes again. It seems to me the more you mess with these openings the more chance there are of creating more problems.

Since you have already made one attempt, cut these access holes, made repairs and still have a substantial leak I will second the above suggestion about building a new tank. You commented about not being able to build a new tank. I think you are selling yourself short. For sure building fuel tanks is somewhat messy but the technique is not any more complicated than riveting any other section of the airplane. It is apparent from your post you already have experience with Proseal so I cannot imagine that would be deterring you. Order the materials from Vans and just build a new tank. You will be much better off in my opinion. I am sure you will find out you really can build it.

Good luck with whatever you decide to do.
 
I completed my tanks about three weeks ago. The olny leaks I had were on the rear baffle to skin about three to five inches in. I only had about three to five small leaks per tank. After much consideration and research, I decided to use the "loctite" fix. I applied a slight vacum, applied a few drops of MEK, let dry for a little bit, re-applied light vacum then slowly applied the loctite as I released the vacum. After a little while a applied a bead of loctite down the whole seam, top and bottom. After the tanks set for a couple of days I re-tested using "ballon" pressure and soapy water. NO LEAKS! It only took a few minutes to fix and it seems to have worked. The only concern I have now is, it seems to easy!......................
 
Since you have already made one attempt, cut these access holes, made repairs and still have a substantial leak I will second the above suggestion about building a new tank. You commented about not being able to build a new tank. I think you are selling yourself short. For sure building fuel tanks is somewhat messy but the technique is not any more complicated than riveting any other section of the airplane. It is apparent from your post you already have experience with Proseal so I cannot imagine that would be deterring you. Order the materials from Vans and just build a new tank. You will be much better off in my opinion. I am sure you will find out you really can build it.

Thanks for the vote of confidence!! But, I did not build the plane, so I have no tools required for building a tank (rivet equipment, dimple tools, bucking bars, etc.) I have built two planes before, a Moni and a Sonex, but they both use pulled rivets, so I really have no experience with solid rivets, although I think I could learn pretty quick. The tools and techniques are where I am lacking....
 
I agree with the other posters on building a new tank. You are spending way to much energy and time trying to correct this problem. If you do not have the tools then I am sure you could find a local RV builder who would jump at the chance to help you out with tools and guidance. That is the beauty of the RV community. My advice is to buy the replacement parts from Van's and recruit a fellow RVer to help. You will fly with much more confidence with a new tank verses one that has had so much modification to it.

Just my thoughts. Best of luck!:)
 
I completed my tanks about three weeks ago. The olny leaks I had were on the rear baffle to skin about three to five inches in. I only had about three to five small leaks per tank. After much consideration and research, I decided to use the "loctite" fix. I applied a slight vacum, applied a few drops of MEK, let dry for a little bit, re-applied light vacum then slowly applied the loctite as I released the vacum. After a little while a applied a bead of loctite down the whole seam, top and bottom. After the tanks set for a couple of days I re-tested using "ballon" pressure and soapy water. NO LEAKS! It only took a few minutes to fix and it seems to have worked. The only concern I have now is, it seems to easy!......................

I have a very small leak that leaves a stain if plane sits for 2 weeks, not worth tearing into everything completely yet. What version of loctite did you use? I am tempted to do this and see how long it lasts. Thanks

Rick
 
.....won't air follow the same path that fuel would?....if there is a proseal breach in the second bay, and the path to the outside is in the fourth bay, how would air help identify the internal proseal breach?
Chris,

Yes, air will follow the same path as fuel. What you are describing is a situation in which a leak develops when two points of failure coexist. One failure mode is the leak path created by a void hidden within the faying surface (the contact area between the flange on the rear baffle and skin) and the other failure mode is a breach in the seal/fillet dam located somewhere along the rear baffle that allows the fuel to find its way into the void within the faying surface. Unlike your analogy, it is highly doubtful a breach in the second bay will result in a leak at the fourth bay. That is a truly long leak path and if that be the case, then the builder was woefully negligent with the proper application of proseal when he installed the rear baffle during initial construction. The more likely scenaro is the leak path is very short, less than inches.

Before you go much further, I suggest you go with the soap bubble test. The long used technique has proven to be a reliable way of troubleshooting leaks. The major airframe manufacturers use soap bubbles for not only for troubleshooting fuel tanks but also for tracing air leaks in pressurized structure.
 
Thanks, Rick, that is the plan. A friend is coming tomorrow or Saturday to take a look. Then I'll drain the tank and do the soap bubble test. There is good info in the 27 Years of the RVAtor on testing, as well as opening the rear bay. The pictures in the book show four round holes, as opposed to the rectangular holes I made.

I have also requested new tank parts pricing from Van's. I'll try to find someone with the knowledge and tools to help me build a new tank, if that is what I decide to do.

Thanks to all for the valuable input.
 
Keep the tank, perhaps replace the baffle...

I don't like your plates but given where you are with repair efforts I would pressurize and test with bubble spray to find the leaks and if any are on the baffle replace it and be done with the access plates... if the leaks are elsewhere fix them and move on.

Either way you can salvage the tank.
 
I don't like your plates but given where you are with repair efforts I would pressurize and test with bubble spray to find the leaks and if any are on the baffle replace it and be done with the access plates... if the leaks are elsewhere fix them and move on.

Either way you can salvage the tank.

Since it's not a pre-punched wing kit, I would carry on with the other ideas presented....:)
 
That was a thought I had, too. How to remove the baffle without damaging the skins or ends of the ribs that are prosealed to the baffle?
 
I completed my tanks about three weeks ago. The olny leaks I had were on the rear baffle to skin about three to five inches in. I only had about three to five small leaks per tank. After much consideration and research, I decided to use the "loctite" fix. I applied a slight vacum, applied a few drops of MEK, let dry for a little bit, re-applied light vacum then slowly applied the loctite as I released the vacum. After a little while a applied a bead of loctite down the whole seam, top and bottom. After the tanks set for a couple of days I re-tested using "ballon" pressure and soapy water. NO LEAKS! It only took a few minutes to fix and it seems to have worked. The only concern I have now is, it seems to easy!......................

Loctite #290 (Green) One post from my search said he has a couple hundred hours on a fix like this with no leaks........
 
Since it's not a pre-punched wing kit, I would carry on with the other ideas presented....:)

The only holes in the baffle that can't be easily match-drilled from the outside are the baffle to inner ribs. Some back-markers would make quick work of those. I don't think it would be hard to fit a new baffle, but getting the old one off is a whole different story.
 
Back
Top