Fuel tank cap cork seal

[Colonel Blink]

I searched the forums, and talk of levering a slim metal ring past the bayonets, or talk of a split pin did not apply.....

So how do I get the cork seal past the sprung loaded disc on this type of filler cap? As can be seen below, my first attempt (trying to fit it like a tyre, with the seal twisted 'conically' to maximise the ID) was unsuccessful.

Do I have to bend up the rim of the sprung loaded 'hat' and then try and bend it back as flat as I can, or would soaking the cork seal in boiling water make it malleable enough to ease on without the excessive tension tearing it? Any advice gratefully received (I can only afford so many £1.99s you know).....

[Ianwilko13]

Looking at the picture I'm not sure that the Cork goes under the rim of the "sprung hat" I think it sits on top, I've fitted a few and not struggled, will have a look at mine and check, best regards, Ian

[Colonel Blink]

Ah.........! Actually, that makes sense from a sealing point of view.

So if that is the case, the seal is held in purely by the two small bayonets?

In my defence, the remains of the one I removed was in the position shown m'lud. I need to be more questioning!!

[Ianwilko13]

Hi Collin, here's a photo of mine, fitted 5 weeks ago and doesn't leak, hope this helps, Happy Easter, Ian.

Screenshot_20240328_195929_Gallery.jpg

[Duncan]

Colin, I have just dismantles a cap like yours, I hope this makes sense, I did this by pushing down one side of the sprung inner into the area under one of the cap side depressions and let the other side rise up to hit the depression on the opposite side, then kept rotating and depressing the inner until it popped out past the depression. I think the inner is not perfectly circular on this cap (even though it looks it) that permits it to be extracted when the ideal location is found, hopefully yours is the same, I would have to remove the split pin to change the washer/gasket.

Petrol Cap 1.jpg

Petrol Cap 2.jpg

[Colonel Blink]

Hi Duncan
Thanks for that! I can't try that on mine at the moment because the tank is brim full of molasses/water mix, and because of a leak through one of the tank badge screw holes, needs to be left at an angle. Removing the cap would have that all over the garage floor! But in a week or so when I rinse that muck out, I will see if mine comes apart the same way.
I tried with the gasket sitting on the tank side of the 'brim' of the sprung hat, but that seems to be tearing it on screwing/unscrewing so I am pretty sure it should be under the brim.
Strangely, my sprung hat doesnt have a split pin in the centre (see pic in my first post)....

[bigwol]

Mine are on top of the lip on the sprung part of the cap

[Colonel Blink]

Top as in when the cap is fitted, or top as when you have the cap off and are looking at it from what would be the inside?

[Colonel Blink]

OK folks, just to complete this thread for any future searchers, here's an update....

Sitting the cork seal 'on the brim' of the sprung 'hat' in the cap didn't work, and the seal was destroyed (see pic below).

As I had a club order to place, I got a couple more seals, which felt more pliable and less 'dry' than the ebay ones I had tried up until now.... probably more elastomer in the mix - they were also much cheaper (which is always a good thing).

The club seal was plonked in some boiling water for a couple of minutes, and with about a quarter of the brass 'brim' bent up a little the seal was relatively easily persuaded to go on without damage. See t'other photo.

As I had cause to fill the tank with water, I put the cap on and inverted it (ain't a full tank heavy?) and the seal held (pretty much).

[Napier]

It seems to me that the Cork seal is required between the cap inner and the tank neck. This creates a petrol tight and sealed closure with only the small hole for venting.
It would seem the seal serves little purpose against the cap outer as you then rely on the tank neck against the cap inner to seal metal to metal. Your test probably showed that the metal on metal seal is adequate but not as leak resistant as with the Cork between the metal surfaces.
Imagine the cap inner without the outer and how it interacts with the tank neck with an invisible spring pushing it down.
I think the damage to the seal might be minimised if the inner is relatively free to rotate. Maybe some lubrication to the back of the cap inner might allow it rotate easily against the spring and resist the turning motion ( ie not move relative to the tank neck when closing) thus not ripping the Cork?