repro triumph tank

[Fraser]

hi guys........

The build, Isaac thought that pre '70's Triumph gas tank would look "HOT" onn that XS650 frame eh.

So bought, and now..... trying to do a petcock eh.

Soooo that tank, true to her natiure comes (we didn't know~who knew ? ) with1/4" B.S.P. Threads eh ? lol lol "H" mmmmmmmm ? that means WHAT ?

The petcocks, I smile every time I type that.... oh sorry... anyhow.....the petcocks (still smiling) they are 3/8"NPT's soooooooooooooooooooo ?

Question : not knowing "math" (left school real early) is there enough meat in those Brit threads to drill out & tap those 3/8" threads then ?

OR do we gotta cut out old & weld new in ?

Thank You for your thoughts Guys....

Fraser

 

[crashcourse]

The major diameter of 1/4 in SP is .518 in. This means that the largest diameter of the threads is .518 in. The drill size to tap 3/8 NPT is 37/64, or .578 inches. So it appears that drilling out the 1/4 BSP with 37/64 will completely remove the old thread, and let you tap with 3/8 NPT. But that doesn't say anything about the material outside the hole, if there is enough there to cut the thread (about .675 inches major diameter) and hold. So it depends: how much material would be left after drilling the hole.

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[maxwell]

............what, eh?!

 

[Fraser]

the steel that is welded in that tank with the threads.... measures 3/4" outside to outside eh..

 

[angus67]

me thinks that would only leave 1/16 of 'meat' around the hole.

 

[Tomterrific]

What about a Triumph petcock? Doesn't that seem like an obvious solution?

www.northerneagle.ca/

Good fella as far as I can tell and in Canada also.

 

[XS1961]

Yeah, I had a Trident tank on my XS many years ago with a simple jumble-find tap(petcock) fitted £5 all in and much better than the Yamaha one!!