Petrol tap adapter

[KenGriggs]

I've used BAP petrol taps on my Sq4 MkII but these are 1/4"BSP threads whilst the tank thread is 3/8" BSP. I fitted adapters 3/8" BSP to 1/4" BSP from the Classic Bike Shop. The hex on the adapters seem to me to be a bit small - the flat on the hex being flush with the thread relief on the 3/8" BSP thread. As a consequence I can't seem to get a perfect seal to the tank. Dowty washers don't seem to do the business, as the rubber inner obviously needs to go over the thread, and there doesn't seem like enough "land" on the underside of the hex on the adapter to get a proper seal.
Anybody else had this problem, and if so how did you overcome it?

Thanks in advance

[Steven.Carter]

Are you using ptfe tape?

[jj.palmer]

The external thread on the adapter that you have described is more than likely a 3/8 BSP tapered, not parallel, therefore has suggested PTFE tape should help it seal, the adapter will only screw in partway before it seals, not all the way up to the hexagon.

Regards,
John P.

[KenGriggs]

No. Definitely not tapered. Also the PTFE tape I tried seemed to dissolve in the petrol.
I've ordered some from another source. They seem from the photo to have a bigger hex., so I'll see if that makes a difference.

[jj.palmer]

If there is no tapered thread for sealing and there is no flange for sealing it makes one wonder what the design intent was of how it should seal, unless it has been made incorrectly ?

Regards,
John P.

[KenGriggs]

Don't know but it's a rubbish design. I got the alternatives today, and they seem to be much better. Much bigger hex. I'll be doing a trial fit tomorrow.

[paul.jameson]

You can seal the threads by using a smear of Red Hermetite. This is the only joint sealant known to resist petrol indefinitely. I tend to put a smear on the threads aS a matter of routine, given the tendency of fibre washers to compress.

[KenGriggs]

I'll be trying Dowty washers, but might use Hermetite as well.

[nevhunter]

Thin fibre washer is not reliable. They invariably crack. Copper or aluminium are better. You can easily make your own aluminium ones on the lathe. Deburr the result so it seals. Nev

[KenGriggs]

Fitted the new adaptors, and got a perfect seal first time using Dowty washers.
For anybody interested, I got them from www.gsparkplug.com