Author Topic: Petrol tap needs help too  (Read 3839 times)

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Offline Michel H

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Petrol tap needs help too
« on: 09 Jun 2014 at 13:10 »
Hello,
Yesterday during rally, I broke the petrol tap of my EW350 (the lever) and I need to replace it.
It's brass petrol lever type similar to this one:

http://www.befr.ebay.be/itm/290833794348?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_223wt_1111

But the tank thread seems to be 3/8" and the pipe thread 5/8". Do you know where I could find one ?
Thank you.
Michel

Offline Chris

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Re: Petrol tap needs help too
« Reply #1 on: 09 Jun 2014 at 14:40 »
Hi Michel
I think that you will find that the thread in the petrol tank is 1/8" BSP (British Standard Pipe) thread which actually measures 0.383" diameter and has 28 threads per inch. The thread at the other end of the tap is probably 1/4" BSP thread with a diameter of 0.518 and 19 threads per inch. This is a common size for petrol taps on Douglas bikes and they are available at autojumbles and specialist suppliers. However, take care in measuring because there are other sizes and combinations of sizes used on petrol taps.  Chris.

Offline Michel H

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Re: Petrol tap needs help too
« Reply #2 on: 09 Jun 2014 at 15:48 »
Hello Chris,
I don't understand 0.383", the diameter is 3/8" Whitworth (9,70mm) and has right 28 threads per inch.
The same, what do you mean 0.518 ", the diameter is 5/8" Whitworth (13,05mm) and has right 18 threads per inch.
Sorry, but I'm not very learned with the various british standard. I thank you if you could confirm the threads are right 1/8" BSP and 1/4" BSP.
On the continent, the autojumbles have not much british tools or others. Do you know a specialist suppliers on the Web ?
Thank you for your help.
Michel.
Michel

Offline Michel H

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Re: Petrol tap needs help too
« Reply #3 on: 09 Jun 2014 at 16:59 »
I found this one:

http://www.befr.ebay.be/itm/330890790740?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_1062wt_1111

As soon as you confirm to me we are right about the sizes, I order it.
Thank you for your help.
Michel.
Michel

Offline Chris

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Re: Petrol tap needs help too
« Reply #4 on: 10 Jun 2014 at 08:24 »
Hi Michel
     Whitworth is a British Standard Coarse Thread having an angle of 55 Degrees on the thread. 3/8" Whitworth has only 16 threads per inch (TPI) The dimension of 0.383" I quoted is only .008" i.e, 8 thousandths of an inch over 3/8" (0.375") and your measurement of 3/8" is probably correct as the threads may have worn or been cut slightly undersize. The fact that it has 28 tpi confirms that the thread is 1/8" British Standard Pipe thread (BSP).
     5/8" Whitworth has only 11 tpi. so the connector on your petrol pipe from the tap to the carburettor is certainly not 5/8" Whitworth. I have just measured six petrol taps of different makes and designs on which the outlet thread is 1/4" British Standard Pipe thread. The outside diameter of the threaded portion of the tap outlet is as I quoted before 0.518" or slightly less a few thousandths of an inch and with 19 tpi. I have a few taps with smaller outlet threads of 7/16" but these are very much in the minority. I have no taps with a 5/8" diameter thread. The tap illustrated in your attachment is quoted as 1/8 x 1/4 which almost certainly means, without saying so, that it has BSP threads. However, the actual illustration does not look as though there is any difference in the size of the threads from one end to the other so the illustration may be just a view of a typical petrol tap made for a petrol tank with a 1/4" BSP outlet. Without personally measuring your old tap I am unable to confirm that the tap on offer is correct for your bike. It is always possible that someone in the past has modified a tap and made a connecting pipe union to suit. However, if you fitted this tap it is easy enough to make up a new petrol pipe with a union nut to suit the tap. I am sorry but unable to supply details of other suppliers on the Internet. Chris.

Offline cardan

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Re: Petrol tap needs help too
« Reply #5 on: 13 Jun 2014 at 03:06 »

Interesting discussion. I would have said that all petrol taps of this size have 1/8 BSP male threads on the inlet, but measuring a range of tapes - Douglas and non-Douglas - I've found that while all have 28 tpi, some are BSP (0.383" or there-abouts) and some are 0.375" (i.e. 3/8-28). Bizarre!

I'm even more confused at the outlet end. Most early (pre-1930) taps are about 7/16" major diameter. All seem to be 19tpi, but some are about 0.430" major diameter, while others are the full 7/16" (0.4375"). I suppose that the 0.428" 19tpi is a pipe thread of some sort, and the other is some form of 7/16-19.

Yes there's only about 8 thou difference between the threads, but there are certainly different sizes! In practice, the different parts could be screwed together providing there is not too much wear.

Leon

Offline Michel H

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Re: Petrol tap needs help too
« Reply #6 on: 22 Jun 2014 at 07:56 »
Hello,
I put the new tap and it's right 1/8" BSP and 1/4" BSP, ouf !
Thank you everybody for your help.
Michel.
Michel