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[Bladh]

Hello all

I wonder if anyone knows what thread it is on the drive shaft of the crankshaft?
I think it is 3/4" 26 TPI but is it BSB or BSC or maybe something else?

The bike is a Royal Enfield 1951 350 Model G

Regards Henrik from Sweden

[Norm]

Hi Bladh, not sure on what they used on the "G" but on the Bullets up till 2008 they were still using Villiers thread

[Presto]

If it's 26 TPI (and that is right) then it is 3/4 inch BCS (i.e. Cycle thread - I've no idea what 'Villiers' thread might be). Cycle thread is the thread on the drive shaft that secures the engine sprocket (sorry I don't know the thread that fixes the drive shaft into the flywheel).

[Norm]

Presto, Villiers were a large English company and as such cut threads in house to whatever they felt suited them. Villiers used all the standard sizes but being entirely in house they added a couple of twists of their own which led to some smaller sizes being a bit vague. As tooling wore it went a little off size. This didn't matter as long as you used genuine Villiers spares as they were equally a trace off size.They also had a partiality for 20 tpi constant pitch threading. This means regardless of screw diameter they threaded it 20tpi. I won't bore you with more details but you can see where it is going and as I said the rotor nut on the Cast Iron Bullets were Villiers thread. I'm guessing the "G" is probably the same but a bigger diameter

[Presto]

Thanks Norm for that. I'm very familiar with Villiers, having lived within a stone's throw of where they were made. I've no idea where the suggestion came from that threads used by Royal Enfield [UK or India] were supposed to be 'Villiers' threads. RE are notorious for using BSC almost everywhere, but also used BSF and, more recently, metric threads. I've nowhere in 60 yrs ever heard them called 'Villiers' thread. Well, we live and learn!

[Presto]

PS - Norm is of course correct - the thread is 20tpi cycle - NOT 26tpi.

[Norm]

Presto, just a bit more trivia, BSW or UNC means you can get away with 1/4 x 20 Villiers, BSF covers the 3/8 x 20,Villiers, 7/16th and 1/2 are covered by UNF. The only Villiers size that has no alternative is 5/16 x 20 but lucky for motorcyclists Villiers didn't use that size too often