Tank cap seal - what to use

[MG]

Hello chaps!

Winter - time for some perfectionist's issues. 

I was wondering what a good material is to make the seal for tank caps from?
The ones with cork tend to leak when they dry out, and I got one cap (Indian repro I think) with soime kind of red rubber ring, which seals the tank perfectly, but will expand when soaked with petrol and hence jump out of the cap when it is opened (which is kind of annoying when it happens at the petrol station).

I was thinking of Viton or similar stuff, any other ideas or hints where to get sheets of suitable thickness (4-6mm)?

Thanks for your input, Markus

[a10 gf]

Tried with different home-made rubber stuff, but ending up using cork.

[MG]

Yep, hence the idea of using NBR, Viton, etc.

[Stu55Flash]

I have the same issue with my tank cap seal. It looks like cork but is rubber. I have to get the cap back on the tank within a couple of minutes else the seal jumps out. I think its something to do with the spring pressure. I have had 2 thoughts on this. One is that the rubber seal needs a harder washer on the top to stop the spring pressure pushing off the seal and also I was thinking of making one out of cork and and coating it with something like waxoil to keep the moisture in. I might give it a go and report back.... next Feb!

Stu

[MG]

A short update:

Meanwhile I could source a sheet of 2mm thick Viton. That is a bit too thin, but with a 1-1.5mm cork ring underneath, it seals the tank perfectly well.
A small piece of it is soaking in a jar with fuel since a week without showing any negative effects. Looks promising.

Cheers, Markus