Tap to clear thread on a G 12 1965 tank

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JEAN-NOEL
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Tap to clear thread on a G 12 1965 tank

Post by JEAN-NOEL »

Hello,
I have tried to fit the fuel taps on my 1965 tank, but I have to clear the theads inside, because it was sealed and painted.
What tap I have to order to do this job ? BSW 1/2 x 14 TPI ? External threads on the fuel taps are approx 1/2. (12.8 mm).
Your advices welcome !
Kind regards.
J.N.
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Rob Harknett
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Re: Tap to clear thread on a G 12 1965 tank

Post by Rob Harknett »

Ewarts appear to use BSP thread, which is confusing as its based on the pipe dia. ????? 3/8 BSP seems to be a common size. This maybe right or wrong for your tap, so perhaps an engineer will be along and confirm this.
This in in tech tips http://www.jampot.com/article_read.asp?id=370
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dave16mct
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Re: Tap to clear thread on a G 12 1965 tank

Post by dave16mct »

I think it will be 1/4 BSP. If you look at this chart:

https://www.newmantools.com/taps/bsp.htm

Dave.
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ajscomboman
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Re: Tap to clear thread on a G 12 1965 tank

Post by ajscomboman »

100% correct Dave 1/4 BSP it is.
JEAN-NOEL
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Re: Tap to clear thread on a G 12 1965 tank

Post by JEAN-NOEL »

Thank you all for your replies.
The suitable tap seems to be 1/4 X 19 TPI.
But I am still confused : 1/4 = 6.35 mm. Is it the internal bore of the fuel tap ? O.D. on the threaded part of the fuel tap = 12.8 i.e 1/2. Taps are branded E.W. Patent.
Looking at Tracy Tools "Tapping Drill Size" catalogue, they state for 1/4 BSP 29/64°, ie 11.5 mm. It could be right.
Cheers J.N.
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Rob Harknett
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Re: Tap to clear thread on a G 12 1965 tank

Post by Rob Harknett »

I was not sure about !/4" thread, as looking at Ewarts info that seemed to apply to taps with a filter + more I did not read. On my bikes I have both sizes, but unless I look not sure which size fits which bike. I believe some even have an adapter that goes in the tank, then a 1/4 tap going in the adapter.
G15 Roy
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Re: Tap to clear thread on a G 12 1965 tank

Post by G15 Roy »

They are two sizes one is 1/8 BSP and the other 1/4 BSP and the later bikes have 1/4 BSP and nothing else unless someone has changed things.
Roy
Andy51
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Re: Tap to clear thread on a G 12 1965 tank

Post by Andy51 »

Hi Jean-Noel, British Standard Pipe (BSP) sizes relate to the size of the hole through the middle, i.e. Pipe size, not the outside diameter (OD), so 1/4 PSP has hole that size, so the OD must be bigger - in this case, 0.518 ins OD, 19 tpi. Welcome to the wonderfully illogical imperial system! Andy
JEAN-NOEL
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Re: Tap to clear thread on a G 12 1965 tank

Post by JEAN-NOEL »

I have just checked the holes in the tank : about 11,3 mm ID. The pitch of the threads on the taps is 19 TPI. So I think that the suitable tap is effectively 1/4 BSP. I will use it very carefully to avoid cross threads !
Thank you very much, Gents, for your help.
Kind regards. J.N.
JEAN-NOEL
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Re: Tap to clear thread on a G 12 1965 tank

Post by JEAN-NOEL »

Hello all,
problem sorted !
I am amazed how hard became the resin to seal the tank ! The maker of the kit (RESTOM) recommend to blind the tank holes vith cork taps. I hink the best way to avoid the problem encountered is to use a suitable lentgh of blanking plus, 1/4 BSP, and remove it before the resin has completely cured, to avoid to tear the coat.
Thank you all for your help.
Kind regards. J.N.
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