Updated 12/13/2015
Keep in mind that you do not prime the inside of fuel tanks. For the following I've assumed you've already cleaned (I use a Extreme Simple Green solution) and deburred all of the parts used in the fuel tanks.
TOOLS & MATERIALS
- ProSeal (or other company's equivalent). I used two types: Class B-2 for between the ribs, stringers and channels and the skin; and brush-able Class A-2 for 2nd coating of the inside seams and rivet heads.
- MEK for cleaning.
- Sealant Removal Wipes for cleaning away stray sealant.
- Maroon colored ScotchBrite pads.
- Popsicle sticks for mixing, applying and spreading ProSeal.
- Small brushes for spreading the ProSeal (buy several). I take a small cheap brush and then cut it down so that it's very stiff (you'll need that for the sealant!). You should also try to pull out any loose bristles before using it, otherwise it'll end up in the sealant in the tank.
- Small paper plates for measuring out and mixing the ProSeal components.
- High quality respirator to protect your lungs when using the MEK. General rule, if you can smell what you're using at all, the respirator isn't up to the task. This is the one I use (I've never smelled anything I use): MSA Safety Works 817663 Multi-Purpose Respirator
- Digital scale to measure the ProSeal components.
- GLOVES! Initially I heard that nitrile gloves were the ones to use, but after seeing mine melt after a little while of use, I did more research. Turns out nitrile is not a good choice at all (terrible actually!). The only two recommended gloves are butyl (expensive) or laminate film (Very Expensive!). Second best is neoprene and latex, which are cheap. My plan now is to use two layers of disposable latex gloves, in which I swap out the outer layer if they break or get much ProSeal on them (which they will).
- Apron. Anything that ProSeal touches will have it permanently...
STEPS
PREP
- Test fit the parts first.
- Ream out all the holes you'll be riveting. Way better to do it now than when they're filled with ProSeal.
- Clean the parts using your preferred cleaner (I use a solution of Extreme Simple Green diluted with water) After you've done that don't touch them again with your hands, only with gloves.
- Disassemble and clean all internal mating surfaces with MEK. Soak all the sealed rivets you'll be using in MEK. Wear your respirator....
- Scruff up all internal mating surfaces with ScotchBrite pad to improve grip of the sealant.
- Clean again with MEK
SEALING
- Check with your instructions, but it's likely easier to put any fixtures in the ribs before you do the next steps of putting the ribs in the skin. Remember to use Loctite and sealant as called for in the instructions.
- Put the skin in the jig and have all your parts ready to go. Don't forget any stringers that have to be installed!
- Mix sealant as per instructions. Generally 10 to 1 if by weight or 10 to .83 if by volume. See this document to learn everything you ever wanted to know about sealant. I measured out the Part A white component (e.g. 20g) and then added the Part B black component right on top of that (e.g. 2g more for a total of 22g).
All mixed!
- Apply sealant along the flanges all the way around the rib, except any surface that is not yet being sealed (generally the back wall of the tank) and spread it out to completely cover the outside surface of the flanges in a thick layer. Like icing a cake. I used the popsicle sticks, which is what I used to mix the components. Some people also put sealant on the inside of the skin where the rib will sit, but I think if you've applied it thickly on the rib, then that is not necessary (saving time...).
- Put the rib into position and start to cleco the holes (all of them this time).
- Using a popsicle stick spread the sealant that has squeezed out from the ribs.
- Once the rib is completely cleco'ed in make sure that any sealant on the outside of the skin is cleaned away with MEK (or the sealant removal wipes). Also clean the inside skin of any stray sealant.
- Repeat with all the ribs.
- Wait a day or two... But, no more than 2 days.
- Starting with one rib, remove every other cleco.
- With a popsicle stick put a dab of newly made ProSeal on all outside the open holes or alternatively just dip the sealed head of rivet into your plate of ProSeal, and shoot the rivets.
- Remove the remaining clecos on that rib and repeat previous step.
- Clean up the outside skin with MEK. Or use the sealant removal wipes if you have those.
- Repeat for remaining ribs and any stringers.
- The next day (or a few days later, doesn't matter, just make sure it's clean, untouched by hands), using newly made sealant, you can go about sealing all the mating edges on the inside of the tank using a brush (my preference) and/or popsicle stick. Get both sides of the ribs and the notches between the flanges. I usually do a run around everything with the thicker Class B sealant then I'll finish up with the thinner Class A to get all the spots which might be hard to get with the Class B. Keep in mind that the Class A type can drip, so you may not want to put that on vertical surfaces.
- Then also apply sealant to the inside rivet heads. Make sure to completely encase the head of each rivet (at least the best you can).
Your tank will probably have 3 fixtures: Fuel pickup, fuel return and a vent. You have to close off two of them and use the third to pressurize the tank (gently). I think the easiest approach is to close off the fuel pickup and return lines and use the vent for the pressurizing.
Here are the two end caps I put on those two lines. You can find them here. My tank used sizes 4 and 6.
And here is the contraption I put on the vent tube. It's 1/4" inner diameter rubber tubing with a tee connector I got from Home Depot. Then I used tie wraps to secure everything. I did need to insert some hard plastic tubing where the balloon attaches since it would just collapse the soft rubber tube.
You may want to tape over your fuel cap to test if it's leaky or not.
Then, using your contraption, blow into the open tube, which will pressurize the tank and then start to blow up the balloon. Once the balloon is sufficiently blown up, use cleco clamps to seal that open tube (I used two to make it secure). The balloon should stay inflated...
Now you need to mix up some water and dish soap to test all the rivets, seams and fixtures.
And here we have a leaking rivet! What you're looking for is any bubbles that grow.
Watch it carefully to see any growing or multiplying bubbles. It's out of frame in this picture, but my fuel return fixture had a slight leak.
And what does a leaking rivet look like? Growing bubble!
Here's a leaking seam. Multiplying bubbles!
Now what?? Well, it's pretty easy to fix the leaks. You have two options:
- Apply Loctite 290 Self-Wicking thread lock and that usually fixes most leaks.
- If the above doesn't work then you'll need to apply a slight vacuum to the tank (see below how I did this), apply some MEK to the leaks to clean them out. Then brush on some thinned (either the brush-able Class A-2 or thinned Class B-2) sealant. Let that suck in a bit, then shut off the vacuum and clean up with MEK.
Let that set for at least three days and then test again...
Good luck!
