Britbike forum Forums British motorcycles in general Bsa gold star forum RGS Tank Bolt Thread

I need to chase the thread for the main fuel tank bolt but I'm not sure of the thread pitch. I'm wondering if anyone knows what this thread is or where the thread pitches and bolt sizes can be located. I'm pretty sure that it's 26 threads per inch but I don't know if it's BSF or some other standard. I also need to buy some thread guages and any info. on which guages are most often needed would be appreciated, Thanks.

I believe it is 7/16 x 26 CEI.


Bill B...

[quote=George M.C.. on which guages are most often needed would be appreciated, Thanks.[/quote]

You need a set of imperial thread gauges, they should come with all the common TPI's, some come marked Whitworth but the thread angles of 55 or 60 cannot be differentiated by eye so do not worry about thread angles. I use ones with imperial on one end and metric on the other, you never know what a DPO has been up to and using 8mm instead of 5/16 is common in the UK.

Search 'Thread pitch gauge' on ebay

In the technical section of this web page are tables of the standard threads found on British bikes
Now Stainless Bits went to the massive effort of compiling lists of all the BSA /Triumph Fasteners by part number and putting them in a table.
Unfortunately Stainless Bits went out of business but the table lives on being uploaded to a variety of web sites & forums ( thought it was actually here )
One of them is Greg Marsh who downloaded the spreadsheets , combined the BSA/Triumph & Norton lists then uploaded them to his web page Greg Marsh
Thus all you need is to consult your parts book for the tank nuts ( in this case ) and drop that into the spread sheet.
Every BSA owner should have a copy on paper in their workshop
Saves hundreds of hours befuddles about actual thread sizes.

So I did a quick search and most of the places that hosted the list have gone which is why you shoul keep copies of these resources
If you use WayBack Machine ( WWW Archive ) you should be able to go to the original site [ Stainlessbits.com ] and download the original pdf table .
The BSAOC also host the list as a spreadsheet . https://tinyurl.com/y3skzrxh
Might see if out Web Master wants to pop a copy of the PDF on our web page

3/8 x 26

Well, at least I had the thread right.

Bill B..

So far , diameters, 5/16" (Kommando), 3/8 "( Chaterlea)and 7/16 "( Boomer)have been suggested.. I beleive it is 5/16 , 26 tpi.

Ok guys,
I dug in my bolt bin and found a NOS 42-8011 Gold Star and A10 tank bolt. The threaded end is 3/8-26 BSC/CEI, whichever name you prefer.



So now George can get back to work on his project.

BSA solved the worn-out threads on the frame's tank mount when they changed to the A65 method: A slotted mount welded on to the top frame tube
that allowed a special bolt to be slipped into it.
From then on, a nut was used to hold the tank to that bolt.
When EITHER the threads on the nut or the bolt wore out, you could discard the bolt and slip a new one into the mount.
Problem SOLVED, no welding needed.

As the mechanic has to remove the tank to do almost anything to the engine's top end, I decided to salvage an A65 tank mount from a wrecked frame.
This will be used on an A10 I have, the stock mount of which is already damaged.

Irish, the worn out thread can be rectified by replacing the bush which screws into another bush which screws into the frame.

Do you have a part number for that thread bush? I didn't see it listed in my 1960 book as a part separate from the frame.

Trev, since the mount is invisible in it's place under the tank, I will go with my plan to change the mount.
I have already salvaged the A65 mount from a wrecked, cut-up frame

Trev, since the mount is invisible in it's place under the tank, I will go with my plan to change the mount.
I have already salvaged the A65 mount from a wrecked, cut-up frame

Stuart,
That part number is 42-4078. Petrol tank fixing bolt socket.

Thanks to all for the information, I have ordered a set of BSC taps and am awaiting their arrival. Also ordered a set of Imperial Thread Gauges.
I believe a PO tapped the tank mount with the wrong tap. I screwed in a new bolt (correct thread) and after about 1/2 inch it started flattening out the leading edge threads (same thing that was wrong with the original bolt). So, I'm hoping that another re-thread with the correct tap with fix the situation. Thanks again for all of your help.

Received the 3/8 X 26 tap, checked the pitch of the bolt with my new Imperial Thread Guage, tapped the tank mount nut and all is well. Previously it was a struggle to get the bolt started, now it almost screws itself in. Came out beautifully, thanks for all of the assistance.