Dynamo strap fixing

No, but if it is smaller than 1/4", it will be an even numbered BA thread.

Hi Steve,

0BA is just a smidgeon below 1/4" diameter at 0.236" x 1mm pitch (25.4 tpi), so 1/4 cycle won't look at it, it's a different thread form as well, I'll have a look at my barrel tomorrow if I get chance and let you know, I'll need to make one up myself, just out of interest, is it a setscrew or a stud and nut?

Hi Steve,

checked my 99 barrel, then had a root and checked another, 500cc, barrel which if memory serves came from a 1953 Model 7 engine, and both were definitely tapped 1/4" BSCy, now possibly they could both co-incidentally have been re-tapped to the same oversize thread, or possibly there were different sizes used during the production run, but that's what I found.

I was wondering if maybe they used an 0BA thread because the dynamo strap assembly was supplied by Lucas, including the clamping bolt, because the ones on BSAs look just the same, but now I don't know, if I were you, I'd just tap it out to 1/4 UNF, Cycle or M6 x 1.0 or whatever you like as long as you get a good thread and make a suitable stud up.

Good Luck!

Why use a stud? An Allen screw is much easier. John.

Hi Steve, almost certainly not original, but that's what what I use on my '54 Dommi. I'm not certain what the thread is, it has probably been re-tapped to 6mm. sometime in the past.

John.

p.s. there is a lot of talk, about the pressed steel chaincases on early Dominators leaking. If properly fitted, they don't! Use a silicon sealer, and don't run the engine for, at least, 24 hours after fitting.

Regarding the chain cases, there was a very good article in Roadholder back in the 1990s written by John Hudson on how to stop chain cases from leaking. A hammer and wood blocks were the tools needed, and no silicone sealant is required.

Colin.

Previously wrote:

Hi Steve, almost certainly not original, but that's what what I use on my '54 Dommi. I'm not certain what the thread is, it has probably been re-tapped to 6mm. sometime in the past.

John.

p.s. there is a lot of talk, about the pressed steel chaincases on early Dominators leaking. If properly fitted, they don't! Use a silicon sealer, and don't run the engine for, at least, 24 hours after fitting.

Never used a hammer on mine, and it doesn't leak! Maybe the earlier ones were better made, before AMC took over.

John.

Nothing to do with Norton or AMC. The primary cases didn't leak without silicone sealer when the bike came from the factory, whether Birmingham or Woolwich. The leaking is caused by owners over tightening the big nut which holds the outer case on and distorting the case. When the owner sees the leak, he tightens the nut more, making the problem worse.

In that case (pun!) I have been either lucky, or, not too brutal. As a teenager, I owned a '53 88, and now have a '54, neither suffered from leaking chaincases (other leaks, yes!). Anyway, old bikes were meant to leak, if they didn't, they had run out of oil! John.

Previously wrote:

Hi Steve,

checked my 99 barrel, then had a root and checked another, 500cc, barrel which if memory serves came from a 1953 Model 7 engine, and both were definitely tapped 1/4" BSCy, now possibly they could both co-incidentally have been re-tapped to the same oversize thread, or possibly there were different sizes used during the production run, but that's what I found.

I was wondering if maybe they used an 0BA thread because the dynamo strap assembly was supplied by Lucas, including the clamping bolt, because the ones on BSAs look just the same, but now I don't know, if I were you, I'd just tap it out to 1/4 UNF, Cycle or M6 x 1.0 or whatever you like as long as you get a good thread and make a suitable stud up.

Good Luck!

Hi,Niall Ireadwithmuch interest your replyto Steve,I am desesperatly looking for a Dommie barrel,dynamo model,exactly yours on the shelf,!!! is it eventuallyfor sale??? might swap with mine ,alternator model,wich was fitted wrong way to my Dommie type 7 year 53,give set of Hepolite pistons with it . W hat do you think of the deal ? , possible or not , ? Thanks best regards Jean-paul e-mail : jeanpaul.berger@sfr.fr