Fuel Tank problem. Need some help

[southwind32]

Need some help from a fiberglass expert.
Evidently the fittings were put in to tight, resulting in the spider webbing.
Once I took the fittings out, I can see the cracks run the depth of the threads, (from the inside to the outside of the tank.
I'm afraid when I put the fittings back in, they will stress and open the cracks.
My thought (for what it's worth) is to enlarge the existing hole, then make a plug, the same thickness of the tank. Insert the plug, securing it with resign. Then lay over glass, extending past the spider webbing slightly.
Once all has set up, drill and tap a new hole in the original position for the fitting.
My explanation probably is confusing, sorry LOL.
I open to suggestions. Please fire away. My experience with fiber glassing is minimal at best.
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Thanks
Brian

[Esser]

Looks like your wings aren’t covered. I would replace them if it was me.

[southwind32]

Looks like your wings aren’t covered. I would replace them if it was me.

Wings don't have covering on them. In fact, yesterday I even pulled the one fuel tank, which wasn't easy or fun. The other tank I'm assuming is cracked too, but I can't tell because for some reason, the previous builder sprayed the area with zinc chromate. I'm going to clean it off today and see how it looks.
This a project that I bought. I'm having to replace the front spar in this wing due to corrosion I found after discovering a rats nest in the covered wing. I have the front spar off. It had been stored for a couple years. I removed the covering from both wings to look them over, just to be on the safe side. The other wing looks great, but not sure about the tank yet.

[Esser]

Not sure what they installed them with but you should be able to take a piece of fishing string and get it between the Spar and tank and “floss” through the RTV fairly easily

[mr bill]

Yup, that's what I did to replace the tanks. I used .016 diameter safety wire and it took awhile, but worked great.

[southwind32]

Just looked at the other tank, and it's fine........no cracks at all. I even pressure checked it and everything is good. Just to be on the safe side, I'm going to replace the one tank that has the cracks.........already have it out so no problems replacing it.

[Guy Buchanan]

Good. I had a long winded, highly technical, labor intensive reply all set to go. I really couldn't face it because I spent all my energy on another post elsewhere.

[southwind32]

Good. I had a long winded, highly technical, labor intensive reply all set to go. I really couldn't face it because I spent all my energy on another post elsewhere.

Perhaps you could share a shorten version. Would help reference my decision......maybe. LOL

[Guy Buchanan]

OK. If I must, I must.

First, well consolidated fiberglass doesn't really spider crack that way. It crushes and delaminates. The circular white spot is the extent of the delamination. Tension failures are tears with fuzzy edges, showing the fabric in the laminate. The spider cracks are probably in a resin pool that sometimes occurs in corners and the bottoms of walls in hand-layups that are too wet. Gravity induces the resin to sag to the bottom of the wall.

So I'm guessing that if you ground the cracks off you'd find they'd stop when you reached the first ply of fiberglass cloth. A repair might look like this:

1. Empty the tank and pull it out.
2. Take out the fitting and chase the threads clean with a tap.
3. Grind the surface until the cracks disappear, or until you have a really huge hole in the tank and then have to buy a new one. (Kidding.)
4. Assuming the cracks were surface, soak the whole area in alcohol to dry it out. Kreem shouldn't be bothered by alcohol.
5. Mildly heat the area to dry out all the alcohol. (Keep it below 140F. Be really careful with an actual heat gun. Use an infrared thermometer. Otherwise just use a hair blow-dryer.)
6. Soak the area in thin cyanoacrylate. IT MUST BE THE THIN STUFF. Otherwise you'll just float it on the surface and get no benefit from the glue's wicking action. If you do it right you should see the white delamination disappear as the glue floods into it. Start at the inside of the threads and work your way out to the surface. Coat the ground surface as well.
7. Sand all the fiberglass 2" outside your repair area for good adhesion for the upcoming fiberglass patch. (It's going to wrap onto the bottom of the tank.)
8. Normally I'd fix these with G-10, but since you're down in the lower corner you're going to have to hand-lay it. Cut 12 circular patches of 6 ounce plain weave fiberglass about 1" larger in diameter than the repair area. Wet these out with epoxy, (not polyester,) and lay them on, being sloppy with alignment and orientation so you get a nice taper on the edges and random orientation. (Don't be so sloppy that the edges get into where you're going to drill your hole.)
9. Let this air cure, then heat it as hot as you can get it with a normal blow dryer. (Not over 140F.) This will help "finish" the cure.
10. We in the marine industry would never, never, never, never, ever tap a composite laminate, but these are just airplanes and safety's not really a concern. I would recommend, however, that you put in a brass pipe thread reducer bushing so that you never have to abuse the fiberglass again. Your fuel nipple will then thread into the brass reducer bushing. (You might want to consider putting in finger strainers as a good safety improvement. That way a 1/2" flake of something nefarious won't be able to shut off your fuel. I use the finger strainers as my bushing, installed with 2-part polysulfide.)
11. To drill and tap the tank for the bushing you first have to locate the hole so the edge of the bushing ends up something above the bottom surface of the tank. Make sure the new hole completely eliminates the old hole.
12. Drill the tank with an acrylic compatible drill bit or a step-drill. (Best not to use a regular drill on any composite, ever.) You're going to drill somewhat larger than you'd normally do for metal, but be careful not to go too large. What you want is for the bushing to be nearly flush when installed barely more than hand tight. Another option is to drill a 1/4" hole first, then enlarge with a Dremel rasp. You might have to do this anyway because of the existing hole beneath your patch. (You could fill the hole before applying the patch, but it's not required and won't really help with drilling the hole.)
13. Gently tap the hope with your NPT tap. If things are getting too tight, re-drill the hole larger. Don't try to enlarge the hole with the tap, as you would in brass and aluminum.
14. Blow everything out, then soak the threads well in thin cyanoacrylate. This will help stabilize all the damage you caused during the threading operation.
15. Once the cyano is dry, chase the threads. Don't cut new ones, though, or you'll have to do the cyano again.
16. Clean the bushing with alcohol, dry, then install using your Hysol 9460. Yes, they're never coming out again. If that makes you uncomfortable then install them with 2-part polysulfide sealant. Snug them down, but don't wrench them. Let everything cure.
17. Install your nipples using two wrenches, one for the nipple and one for the bushing. Never load the bushing / tank threads or you'll have to re-seal.
18. Finish the plane, go flying, come to Ramona, say "Hi!".

Long enough? I certainly hope so.

[southwind32]

Thanks for the info, that's all very interesting. One thing about the cracks, I can't feel them on the surface. If I'm understanding you correctly, they would typically be just under the surface at the first layer of material. One other thing, when I removed the fittings, the cracks ran from the outside to the inside of the depth of the threads......or nearly so.