Solving Filler Cap Leak

My filler cap leaks a fair bit when fuel sloshes around. So much so that if I fill my tank up anymore than 2/3 full, normal vibrations and such will cause gas to be splashed all over the left side of my tank.

It's not coming from the gasket at the fill top. The cap has two sections, the cap itself is the top section and the lower section is a collar that wraps around the filler neck on the tank. The collar has a lip on it that is slightly smaller in diameter than the tank filler neck itself. The gasket on the cap rests on this lip, and that junction is pretty much leak free.

What's not leak free (I think) is the mating between the collar and the tank itself. Gas splashes up and comes down between the filler neck and lower section lip, spilling on the side of the tank. I'm not sure how the collar is retained on the tank either (threaded collar or perhaps some sort of epoxy/adhesive?). I've put a bit of force on it to see if it is threaded with no success, and don't want to put more on for fear of damaging something unless I'm sure it's threaded...

What to do? Tank was purchased from RGM, it is a alloy manx style tank with Monza cap.

- Apply some sort of sealant or epoxy that is immune to gasoline fumes on the inside of the filler where it meets the lip of the collar.

- Alternatively, I could go ahead and actually remove the fill cap lower section and properly seal it up to the tank. How to take it off and what sort of sealer to use I'm not really sure. If it's threaded I think plumber's tape would dissolve quickly?

Thoughts?

Cheers,

- HJ

Here's a photo of the collar to give a visual. In the filler neck you can see some remnants of a sealer I had previously applied to the junction that cured the leak for a short period of time before peeling off by hand (touted as resistant to gasoline... not so much).

That looks like a normal "Monza" filler cap-so the cap section screws off, and I believe there should be a gasket (or two?) to seal the joint between the parts.

Update from RGM... they say the caps are glued into place with a two part epoxy (Araldite). They said it's also possible the weld where the filler neck comes up is leaking...

So looks like I'm stuck with option A, sealant/epoxy. Any good recommendations for fuel resistant epoxies? Would not be immersed in fuel, but would have to stand up to fuel vapors. JB Weld or JB Stick?

http://jbweld.net/products/jbstik.php

Cheers,

- HJ

I know hobot would recommend JB Weld, but I don't have any experience there, maybe he'll pipe up.

Dave
69S

Yes JBWell is up to this job and have used it to seal two crash holed fiber glass tanks, one my own, one my buddies a few years ago with his tiny HyRyder tank getting as much alcohol fuel as w/o. BTW the black part of JBW is steel dust filled so can use magnets to guide its flow but can also suck it around an edge to gunk up job. I'd use hair dryer to expand the pieces for removal 'ease'. I put a disc magnet under small blob of JBW to mix as it draws it all back to a raised button instead of spreading out to try to pull back to scoop up.

JBW can take over a day to really set up so let it sit in sun a few days after stiff before gassing up. JBW is mainly a mechanical bond not an adhesive so roughen the surfaces as well as degrease. I use picks to triangle files to a vibra tool pecker.
Mask surfaces you don't want scared as JBW is too adhesive on stuff you'd not like it to be, ugh.

The jbw will definitely remain cured when immersed in E10. It is the only non-solvent curing mixture that I had handy and actually have tried. I cannot make it stick to aluminum when immersed however, it lifts and peels off overnight. The aluminum was cleaned with a ketone wash and subsequently air dried immediately prior. Maybe after an oxide forming period of time it may adhere better.
All solvent cured sealers will fail overnight also, regardless of how they may tout being gasoline resistant. None of a half dozen or so worked for me at all, gasoline being a powerful solvent should have made the light go on sooner but I'm not brilliant.
It seems that chemical cross linking is needed to be E10 resistant so other two part mixtures may work also. I would like to try a two part urethane, they have great potential as adhesives.

Thanks for the help. Will go with JB Weld. I think I also ran into trouble with the last sealant by letting it cure in the presence of fuel vapors. Will thoroughly drain the tank before the next repair.

The inside of the lip has a slot in it where it meets the filler neck. So I think once the JB Weld flows in there and hardens it should be in there pretty firmly. I guess I can run some sandpaper over the area too. From what I understand, the ethanol in gas dissolves aluminum oxide, so not sure there is much of any oxide for it to stick to.

Cheers,

- HJ