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#841338 02/27/21 6:00 pm
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Danam Offline OP
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After sealing a 1970 a65 gas tank with POR15 I made sure not to get any on the petcock hole threads but of course the next day some had dribbled out. Now it’s dry and i need a solution. I was thinking of a 3/8 tap but is this Whitworth? Do they even make Whitworth taps? What can I do?

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I had to tap the holes on a fuel tank that takes that size petcocks (to remove some epoxy primer). I got the tap from British Tools and Fasteners - it is British Pipe Thread, 1/4 X 19 tpi. (Note, it is sized by the i.d. of the pipe.)


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
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Originally Posted by Mark Z
I had to tap the holes on a fuel tank that takes that size petcocks (to remove some epoxy primer). I got the tap from British Tools and Fasteners - it is British Pipe Thread, 1/4 X 19 tpi. (Note, it is sized by the i.d. of the pipe.)

correct it is BSP

if i ever need a tap (which is rare cause i have lots left over from my days in the trade) im only going to use a few times . specially for just cleaning out a thread I try the second hand tool places , BSP ( here anyway) is a very common size and i can imagine it isn't that unusual in the USA ? ........they will cost $5 instead of how much new from some bike bits type supplier ?


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i did the caswells thing on my T120 and to clean petcock threads took a bolt the same size and cut a slot in in with dremel tool it worked great po boy solution


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If you leave the tank upside down when you’ve drained the sealant out. It’ll save the dregs from pooling around the threaded area.

Taps used on A65’s were either 3/8BSP OR 1/4 BSP, so it depends which tank you have. The peanut tank and the bulbous 4 gallon tank are 3/8, the scalloped tanks (2 types) I believe are both 1/4, the smaller one definitely is.


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Originally Posted by Allan G
If you leave the tank upside down when you’ve drained the sealant out. It’ll save the dregs from pooling around the threaded area.

Taps used on A65’s were either 3/8BSP OR 1/4 BSP, so it depends which tank you have. The peanut tank and the bulbous 4 gallon tank are 3/8, the scalloped tanks (2 types) I believe are both 1/4, the smaller one definitely is.

U.S. chrome A65 tanks (2 1/2 gal?) had 3/8" taps in 1967 (and presumably before that), but changed to 1/4" shortly thereafter (1968 I think, but definitely by 1970).


Mark Z

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Originally Posted by Mark Z
Originally Posted by Allan G
If you leave the tank upside down when you’ve drained the sealant out. It’ll save the dregs from pooling around the threaded area.

Taps used on A65’s were either 3/8BSP OR 1/4 BSP, so it depends which tank you have. The peanut tank and the bulbous 4 gallon tank are 3/8, the scalloped tanks (2 types) I believe are both 1/4, the smaller one definitely is.

U.S. chrome A65 tanks (2 1/2 gal?) had 3/8" taps in 1967 (and presumably before that), but changed to 1/4" shortly thereafter (1968 I think, but definitely by 1970).

I have a 70 tank, still used 3/8 BSP


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68’ A65 Lightning “clubman”
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67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Danam #841509 03/01/21 11:57 am
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Original poster was from the US, so just a note on BSP vs NP (T or P).
Just about all the world still use BSP as the standard for pipe thread, even in this metricated, world EXCEPT the good old US of A who have their own standard. The main difference is the pitch angle, 60 degrees for NP and 55 for BSP. In my experience, and in small sizes like this, and low pressure like this, it makes naff all difference. So running a 1/4 or 3/8 NPP tap, which you can get easily in SF, up the threads should it sort out. At very worst option a wrap of PTFE on the tread (in addition to a new fiber washer) to "take up the slop" would be needed. If you do, use the yellow kind, the stuff for propane / hydrocarbon use.

Danam #841511 03/01/21 12:02 pm
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The TPI's also differ between BSP and NP threads so an NP petrol tap in a BSP fitting will not work.

Trade Size Pitch (Threads per Inch)
NPT/NPS BSP
1/8 27 28
1/4 18 19
3/8 18 19

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I've used NPT taps on fuel tank petcock threads with no issue. No leaks.


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Originally Posted by Allan G
Originally Posted by Mark Z
Originally Posted by Allan G
If you leave the tank upside down when you’ve drained the sealant out. It’ll save the dregs from pooling around the threaded area.

Taps used on A65’s were either 3/8BSP OR 1/4 BSP, so it depends which tank you have. The peanut tank and the bulbous 4 gallon tank are 3/8, the scalloped tanks (2 types) I believe are both 1/4, the smaller one definitely is.

U.S. chrome A65 tanks (2 1/2 gal?) had 3/8" taps in 1967 (and presumably before that), but changed to 1/4" shortly thereafter (1968 I think, but definitely by 1970).

I have a 70 tank, still used 3/8 BSP

Yow, I'm wrong again! Danam, please review - I had stated 1/4" by 19 BSP for your tank, but Allan claims BSA was still using 3/8" taps in '70. Check the i.d. of your petcocks before ordering a tap!


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No worries, it’s definitely 3/8. I have 1/4 petcock with adapters. I can’t find 3/8 A65 petcocks anywhere!

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Originally Posted by Danam
No worries, it’s definitely 3/8. I have 1/4 petcock with adapters. I can’t find 3/8 A65 petcocks anywhere!


G / R
size Thread
density
(TPI) Thread
pitch Major
diameter Minor
diameter Gauge
length Tapping drill
R 95% G 80%
(in) (in−1) (mm) (in) (mm) (in) (mm) (in) (mm) (mm) (mm)
​1⁄16 28 0.907 0.3041 7.723 0.2583 6.561 5⁄32 4.0 6.6 6.8
​1⁄8 28 0.907 0.3830 9.728 0.3372 8.566 5⁄32 4.0 8.6 8.8
​1⁄4 19 1.337 0.5180 13.157 0.4506 11.445 0.2367 6.0 11.5 11.8
​3⁄8 19 1.337 0.6560 16.662 0.5886 14.950 1⁄4 6.4 15.0 15.3





ok so i cant make the chart copy properly but the 0.6560 " refers to the diameter over the thread so it is clearly 3/8 BSP ...i have a 70 A65 tank and there is no question that is what it is ( I also have a UK home market A65L 70 tank which are as rare as, they look like the firebird tank but are bigger ...only ever came out for the 70 A65L , that is also 3/8 )

you are having problems finding the petrol taps in 3/8 because as far as i know only BSA used them , lesser makes did not ASAIK so grab them when you see tha at a swap meet or where ever

but nothing wrong with your use of an adaptor other than cosmetic for the pedants ...but who cares when you out on your bike in the sunshine right!

to quote John Wayne "a mans gotta do what a mans gotta do" ....that quote is often wrongly attributed to Ronnie Regan but nope it was the Duke that said it first ( just thought you needed to know that hah


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Admittedly this one costs quite a lot. But here you are eBay link


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Or if you have an old petrol tap that is past it's best, do as above, cutting a cross slot and maybe squeeze the top inwards a tiny bit. Then use it to clear the threads.

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POR 15 is very thin
Good chance the petcocks will screw in no problems


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Originally Posted by Danam
No worries, it’s definitely 3/8. I have 1/4 petcock with adapters. I can’t find 3/8 A65 petcocks anywhere!

I did the same thing on my A65 bitsa with '67 fuel tank - it allows for a wide variety of aftermarket petcocks (i.e., ones that actually work and don't leak).


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Originally Posted by AngloBike
Or if you have an old petrol tap that is past it's best, do as above, cutting a cross slot and maybe squeeze the top inwards a tiny bit. Then use it to clear the threads.
That's what I use to plug the holes in the first place. Then drain the liner out the filler hole and remove the old taps before it sets up.
I also found a 3/8" BSP tap at British Tools and Fasteners for not too much money.


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