Saving Old Seagulls

I bought a blank fueltankcap (BSA) from ceandress and want to know how the vent works?
Is the air passing through a hole in the side, or through the tread?
regards Jan

Hi Jan, l believe those are now used as oil tank caps on motor bikes. Does yours have a side breather hole? You could always drill and tap a hole in the centre (if there is enough meat) and then screw in a bolt. If you drill the bolt up the centre with a 1/16th bit or similar from the thread end and stop before you come out the hex end and then drill in sideways to meet the centre hole you will then have a breather that can be screwed down to seal the tank. A fibrous washer will help seal to.

Is it bayonet or thread?

Happy mooncake day everyone

Ceandess sell several types of cap, domed or flat top, with or with vent hole, and in 2 sizes. The ones with a vent hole are designed for peterol tanks, that generally do not have a breather. The ones without a vent hole are generally for classic bike oil tanks, which usually have a breather system built into the oil tank.

The vented ones have a small drilled hole in the inner diaphragm, around 020" this is to allow fuel tanks to vent. Here's a new one before the vent hole is added, with a replica air vent.

The originals were chromed brass, the new ones are chromed steel. Ceandess have been making these since the 1930s

thanks hugz and oyster 49,
i have the same cap in your picture with no vent.
I would like to make a replica air vent for the cap, but how does the vent work?
i know the needle opens a hole in the centre, but were does this vent to?
cheers Jan

There is a tiny vent hole in the side of the air vent. When you tighten the screw, no air can vent through this hole.

Hello Oyster 49,
If i understand this correctly there is a tiny hole in the side of the airvent wich breathes in between the inner and outer cover of the cap.
Do you have a picture where the hole is?
Thanks Jan