Fuel Cap Disassembly

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RBW
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Fuel Cap Disassembly

Post by RBW » Sun Apr 24, 2022 6:04 pm

Interested to know any tricks to disassemble a Mule fuel cap. I replaced the rubber gasket below the cap that seals against the fuel tank filler neck. The brass cone washer above this gasket holds the gasket against the filler neck. On my fuel cap, this brass cone washer is no longer secure and moves around a little underneath the cap. When the tank is fairly full, the fuel will slosh and leak down the filler neck. I assume this is because it is working its way above the brass cone washer that is supposed to be secured to upper portion of the cap. I am also wondering about disassembly so that I can re-seal the vent valve. It looks like there are some portions of the cam that are soldered together. I figure the Army just had a large supply of fuel caps and that the expectation was to just throw the whole thing away when this happened. Thanks for any help.


markrdje
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Re: Fuel Cap Disassembly

Post by markrdje » Sun Apr 24, 2022 6:44 pm

M274A5 Fuel Tank.png
This is the pic I can find, tomorrow I could take a pic of my mule gas stick
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RBW
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Re: Fuel Cap Disassembly

Post by RBW » Mon Apr 25, 2022 8:23 pm

Thanks. I think I have a start on it. It is definitely not designed to be serviceable. Bottom section (with dipstick attached) is soldered into the portion of the cap with the ears that engage the filler neck. Have to heat to melt solder, then pry this away from the upper section. Vent valve can be disassembled, but mushroomed end of vent tab has to be filed off and pin pried out of tab. This allows the vent valve to be removed. Seal is pressed in place in vent valve, but could be replaced with viton sheet if needed. Vent valve housing has its own gasket that will be destroyed by heating the solder. This allows the vent to actually seal fuel inside the tank (hypothetically) if the vehicle is flipped on its side. Now, to access the brass cone spring, the portion of the upper cap with the tabs to engage the filler neck must be removed from the inner portion of the upper cap. The brass cone is attached to the upper portion of this stamping. I haven't gotten this far yet, but to separate the stamping from the inner portion of the upper cap, the extension of the the upper cap with the vent hole must be ground away (this would have to be rewelded later). The inner portion of the upper cap appears to be soldered to the outer portion (the one that has the stamped lettering and the tabs on later models). This does not need to be disassembled. I'll see if I can get it all back together.

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Re: Fuel Cap Disassembly

Post by markrdje » Tue Apr 26, 2022 8:28 am

#1 fuel cap.png
#1 fuel cap.png (30.87 KiB) Viewed 1918 times
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markrdje
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Re: Fuel Cap Disassembly

Post by markrdje » Tue Apr 26, 2022 9:05 am

Aw, I don't think my picture helped you at all
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RBW
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Re: Fuel Cap Disassembly

Post by RBW » Wed Apr 27, 2022 8:59 pm

Well, I got it figured out. The question is, how many hours is it worth to stop a leak from a fuel cap that the Army never intended to be rebuilt.

From top to bottom, there is an outer cap (the one with the tabs and lettering), an inner cap (soldered to the outer cap), a concave stamping with the locking tabs and a brass cone washer soldered to the top (pinned to the inner cap with a hollow square shank stud staked on both sides), and a stamping that contains the vent valve and dipstick (soldered to the stamping with the tabs).

My brass cone washer, which holds the fuel cap gasket against the filler neck, had broken free from the stamping with the locking tabs. To get to this, it is necessary to melt the solder holding the dipstick tube/vent valve assembly to the locking tab stamping. There is a gasket between these pieces that will likely be melted during this process. The locking tab stamping is pinned to the inner cap. I had to mill the flared portions of this pin away to allow the locking tab stamping to be pulled off this square shank pin. Once that was free, I was able to press on and re-solder the cone washer to the locking tab stamping. The solder should go all the way around, since this and the filler neck gasket are what keep the fuel from getting past the cap. To reattach, it was necessary to spot weld the square shank pin to the locking tab stamping without getting the stamping hot enough to melt all the solder away. The dipstick/vent valve assembly can then be re-soldered to the locking tab stamping.

If I did it again, I would find a way to clamp the locking tab stamping against the inner cap better - since this was originally staked from both sides, any slop will lead to some looseness between the cap and the locking tab stamping, but this does not contribute to leaking. The filler neck gasket also tightens this up a bit when the cap is locked. It is not possible to stake this pin without separating the outer cap from the inner cap, something I was not willing to do because I figured I would destroy it in the process or at least ruin the original paint, which seems to be extraordinarily durable and has a nice patina.

Quite a lot to deal with just to fix an old fuel cap, but I filled the tank 3/4 full, took the machine for a hard run afterward, and didn't have any leaks, which is a first.

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Re: Fuel Cap Disassembly

Post by camoyj7 » Tue Feb 07, 2023 8:28 am

I ordered a new seal from John Emery. After I removed the old seal I soaked the new seal in hot for a few minutes. While the seal is hot I was able to stretch it on to the cap. I had to stop every few minutes and dip the whole cap with seal in the hot water to soften it up. John said it would go on and he was right!
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