C15 tank mounting bolt & chainguard

[shoal48]

Hi all, I'm just looking for some measurements. Im still rebuilding a '61 c15 which was just boxes of bits which haven't been a complete bike for over 30 years.

I'm gradually collecting the bits I need but am short of the fixing bolt for the fuel tank. It seems a 5/16" coach bolt will have a suitable slim head and square shank but I need an overall length for the bolt and also the lengths of the 2 spacers.

The bottom one is 40-8090 I believe & I have read its 1 7/8" long but confirmation would be helpful.

the upper spacer 40-8089 fits in the rubber bush to stop over compression of the bush, someone said they thought it was 7/8" long but that would allow the bush to compress quite a long before the washers either side bottom on the sleeve so a proper dimension would help a lot.

One other thing I need is a chainguard if anyone has one they would like to sell.

thanks

 

[limeyrob]

All these parts are available, just £2-3 each.   Google search the part number preceded by BSA.

[iansoady]

Don't use a coach bolt as it will have a metric thread. As Rob says, the proper parts are available from draganfly etc.

[limeyrob]

Trigger warning - "metric thread".  One of my pet hates is a metric thread on a BSA.

[shoal48]

All these parts are available, just £2-3 each.  Google search the part number preceded by BSA.

Draganfly was the first place I looked, they have the distance pieces, just under £10 for the two and I was intending to just buy the bolt and the distance pieces but the bolt is on back order with no firm restocking date and other sellers on ebay are out of stock for the bolt. This is when I thought I could I could recreate a bolt by using a long 5/16" coach bolt, grind the head flat the same as the original part, cut it to the right length, put the correct thread on and replate it.  I have the right gauge tubing for the distance pieces so, if I am making the bolt its easy to make the distance pieces, just need the correct lengths. 

[shoal48]

Trigger warning - "metric thread".  One of my pet hates is a metric thread on a BSA.

No worries, thats one of my pet hates as well. The correct part is out of stock everywhere which is why I thought I would try and replicate it. My thinking is get a long enough 5/16" coach bolt to be able to cut off the threaded section completely to get the right overall length & then cut a 5/16" BSC 26tpi thread for a couple of inches. I would probably need to reshape the mushroom head on a coach bolt to the flat profile of the original and then re-plate it.

[shoal48]

Don't use a coach bolt as it will have a metric thread. As Rob says, the proper parts are available from draganfly etc.

The problem is that Draganfly, my normal go-to, is out of stock and the bolt is on back order with no firm date for restock, there are a couple of other suppliers on ebay but they are out of stock as well. I wouldnt use a metric thread on the bike, my theought was to source a long enough 5/16" coach bolt to be able to remove the threaded section in getting it down to the right length then put a 5/16" BSC 26 thread on the end to replicate the original, probably reshape the head as well & replate it.

[limeyrob]

OK that all makes sense. I looked at the Cub faster list and 40-8037 is 5/16 CEI x 4" which gives you a start, no more detail.  Try Bantamspares.com as I think its the same bolt
https://www.bsabantamspares.com/shop/p/40-8037

[shoal48]

OK that all makes sense. I looked at the Cub faster list and 40-8037 is 5/16 CEI x 4" which gives you a start, no more detail.  Try Bantamspares.com as I think its the same bolt
https://www.bsabantamspares.com/shop/p/40-8037

thanks Rob, I will have a look.

[shoal48]

OK that all makes sense. I looked at the Cub faster list and 40-8037 is 5/16 CEI x 4" which gives you a start, no more detail.  Try Bantamspares.com as I think its the same bolt
https://www.bsabantamspares.com/shop/p/40-8037

thanks Rob, I will have a look.

The plot thickens,  Draganfly lists the c15 bolt as 40-8075 at 4", it shows the 40-8037 bolt as 3 1/4" long and pic shows the same circular flat head with square shank inboard to engage the mounting bracket slot. They are both on back order. I just looked at my original BSA spares catalogue and it shows the correct item is 40-8037, as you suggested.
Bantam spares shows the 40-8037 bolt as 4" and for a C15, but with a plain hex head which wouldnt work as it needs the square shank. Not sure if they have put up the wrong pic. I will get in touch with them to see if the bolt in the pic is what they are selling as a 40-8037

[limeyrob]

One of the most useful things I bought was a set of CEI dies in 1/4, 5/16 and 3/8.  Didn't cost a lot off e-bay but have paid for themselves many times over. 

[shoal48]

One of the most useful things I bought was a set of CEI dies in 1/4, 5/16 and 3/8.  Didn't cost a lot off e-bay but have paid for themselves many times over. 

completely agree, I got those 3 sizes plus taps when I started rebuild, invaluable. I also got helicoil set to repair stripped engine screw threads

[Tigerfeet]

Hope this helps (The other parts are with my tank).

Also you might want to download this publication as an excel file. I use it endlessly. virtually every fastener on a BSA or Triumph is detailed. diameter, length, threadform, tpi...  https://commons.princeton.edu/60-3-tiger-cub/wp-content/uploads/sites/440/2025/03/Triumph-Nuts-and-Bolts-Reference-Guide.pdf