Ariel Owners Motorcycle Club

Perhaps a niche question - my 1920 roadster has a petrol cap with a glass in it. I cannot see any mention of gaskets on the parts list, nor did it have any when I got it (or any glass...). Of course you don't want to stop air getting in to the tank but also don't want fuel sloshing around.

Now - does anyone with an early bike know if there should be a gasket or two in the cap?

There does not appear to be a gasket as such on my cap. If one tightens it up the bike will stop and then start after 20 minutes or so. I gather from chatting at Banbury that this is very common and was shown all sorts of ingenious holes drilled - I just left it slightly loose and all is well....

If you don't seal a cap the Paint will suffer. It needs breather holes and a double chamber in the cap and don't completely fill the tank. When the Later tank caps come loose you think there's something wrong with the Bike, It rattles that Much. Nev

Mark - I think that is my plan - slightly loose glass.

Nev - the pain t won't suffer - its 2k lacquered which has proved to be resilient this weekend. And I don't want to modify a 106 year old part unnecessarily.

I thought that the cap with glass was used on the oil side.

rein.heerkens wrote: Mon Jun 15, 2026 7:26 pm I thought that the cap with glass was used on the oil side.

Looking at the 1919 sales literature it says 'large filler caps, petrol cap with glass top'

On my 21V the oilfiller cap has a glass and the petrol cap is closed with a breathing hole.