Help with Petrol Taps

[Craig]

Hello

Image below is of the petrol taps fitted on my bike - 1949 A7.

Wonder if anybody else has these on their bikes and can help with sizing. From what I can find and read,

Tank side has 3/8 BSP thread and the adapter is this size with the filter attached. Going into that adapter (from the tap) is 1/8 BSP thread.

Is the thread on the petrol pipe side 1/4 BSP? I measure the thread diameter as approx 0.480". But I know this is not how gas thread works (it is not the diameter of the thread)

According to parts book - 67-8092 is the correct part number but I am guess this is not the same as mine - I don;t have image of that - anybody know what they are?

My taps are leaking and cannot get them to stop. Guess the taper is worn and time to replace them but want to make sure I get it right.

Appreciate any help.

[Billybream]

Hi Craig.
Please see explanation copied from Dragonfly data sheet which covers BSP threads very well. BSP although an old thread form is still internationally used today and is based upon the ID of the pipe.

"All A, B, 3/8 BSP thread in for the tap. Initially the tank end of the tap was without a filter and had a 1/8 BSP thread that screwed into an adaptor with a 3/8 BSP male thread and a filter. It was this that screwed into the tank. Later taps were fitted with a filter and had a 3/8 BSP thread and d with the adaptor.
Most taps had a 1/4 BSP threaded outlet and originally used a rigid copper pipe with soldered fittings. For a few years the A group used a spigot on the lower end of the tap and a 'banjo' fitting on the petrol pipe.
Where a tap, at the time of writing, is not available a suitable alternative is suggested, however as new items are being discovered all the time it would be wise to check the price list for current availability.
The sizes given with the taps listed are British Standard Pipe or BSP thread sizes, tank end is given first then the outlet. A tap with a 1/8 BSP thread will need the 27-8436 adaptor with filter or A16-96, a tap with a 1/4 BSP thread will need the A16-90 adaptor. BSP thread sizes are confusing because the size relates to the size of the pipe not the thread. Nominal thread sizes are as follows (male then female):- 1/8 BSP .375, 0.35; 3/16 BSP 0.425, 0.375; 1/4 BSP 0.515, 0.468; 3/8 BSP 0.650, 0.609. All sizes of threads are 19 TPI except the 1/8, which is 28."
 

[chaterlea25]

Hi, Craig,
The fitting on the lower end of the tap is peculiar and not a standard BSP thread,
It is sometimes called 3/16BSP but I have never seen a reference to that thread 
It measures c0.5in. x 19tpi
Original taps and fittings as in your photo are available from Autocycle engineering in Birmingham
and maybe other places?
The taper taps can be prone to leaks made worse by previous attempts to lap the tapers with abrasive 
good or new taps  benefit from the occasional lube with a special petrol proof grease

John

[scotty]

Hello Craig

i was struggling to find fuel taps that did not leak

If you are not bothered about originality consider these style taps

I have them fitted on my A & B with no leaks

They're not cheap but they do the job and do not leak

I'm sure wiser guys than I can recommend non leaky more original looking taps

S

[duTch]

 I started this yesterday but workand flat battery interfered, so;

Yep- I'm using gas taps like that bought at a gas shop.
 If same as mine, the outlet takes a standard olive/spigot that I soldered copper pipe into, spigot is held in with its retaining nut. Trouble is I could only get hold of ones that took 1/8" or 3/16" (?) copper, which I deemed not big enough to supply well, so packed them out to take 5/16"-8mm hose.

   I last bought replacementsfrom Industrial Fitting Supplies/Sales (IFS) who do gas fire and air supplies only. A point to note is to use BSPP (parallel thread)on the adapter into the tank, as it's possible to over-tighten a taper thread and split the outlet.  .

 Is probably easier to buy proper bike fuel taps though