Nut sizes

[Woods4900]

Does anybody know the nut size and thread for the nut that’s at each end of the engine mounting spindles please I’m one short with my project ,cheers .

[Geoff Case]

I think I am correct in saying the long engine bolts are Cycle Thread form, 20 threads per inch. (5/8 diameter) Some Brum Scotts seem to use BSF threads.

[BRIAN MARSHALL]

The Spares Scheme have replacement nuts and half-nuts (locknuts) at 5/8″ diameter and 20 TPI. Just occasionally I’ve seen them at 26TPI. Can’t remember what was on my Brum Scott, but I’m sure that Geoff is correct that some would have been 5/8″ BSF.

[Stan Thomas]

Just to confuse us, 5/8 x 20tpi and 5/8 x 26tpi are both designated cycle threads – but the Birmingham Scotts had 20tpi threads as Geoff says – as I made some new engine studs a few months ago for someone on my rotary chisel.

[BRIAN MARSHALL]

At diameters above about 1/2″ British Standard Cycle Thread lists two alternative pitches, 20tpi and 26tpi. This is a throwback to the days of the old CEI thread, (Cycle Engineers Institute). The CEI and BSCY threads were amalgamated, and both pitches were kept. Both are Whitworth thread form.

[Clawed]

Sorry Brian but CEI (and BSC) is not quite Whitworth form. They have a 60 degree thread angle not 55, but do have the rounded tops and bottoms that Whitworth has. There are also some 28 TPI threads over 1/2 “, (mainly steering head in 15/16″, 1″, 1 1/16″ and 1 1/8”) and bicycle bottom bracket assemblies may have 30 or 32 TPI, I cannot remember. Bottom brackets also come in various sizes and left and right hand threads. And don’t forget spoke threads are CEI threads. BSC is CEI with some of the weirder, (less preferred) sizes taken out.

Strangely enough, even though many say it is a weird thread, it is about the only world wide thread. As best as I can find, bicycles from the UK, France, USSR, USA, China, Japan and everywhere else I can find use CEI.
Bicycles have united the world. (Nice dream).

Geoff

[nickh]

@Clawed wrote:

(snip) Strangely enough, even though many say it is a weird thread, it is about the only world wide thread…………..
………Bicycles have united the world. (Nice dream).

Except Raleigh who went their own way, at least on bottom brackets and steering heads!

NHH

[BRIAN MARSHALL]

And for several decades, Raleigh, here in Nottingham, were the world’s largest producer of bicycles, and BSA over in Birmingham, were the world’s largest producer of motorcycles, plus guns, and various other things. We have lost it all…

[BRIAN MARSHALL]

I have a nice wooden boxed set of BSCY taps and dies, ex-War Department, that I’ve had for at least 50 years, and in amongst the contents are 9/16″ x 20 tpi, left-hand thread taps. I suppose that the BSA M20, the standard fare of the Army despatch riders during the war and into the early 1960s, must have had such a thread somewhere, or they would not have been included in the set ? ( I can only think of pedal cycle crank thread, so perhaps the Army workshops were also fixing pedal cycles ).

[Geoff Case]

Brian, talking about his “nice set of boxed BSCY taps& dies”, reminded me of a story from about 30 years ago. A boating friend was looking at stuff for sale , as he did boat jumbles at the time. He told me there were “several old bikes ,in the over grown back garden”of a house. I hot footed to Riverside, in Cardiff to find 6 bikes. Trouble was they were in the middle of an elderberry tree which had grown through them over many years. Only a couple of rusty rear number plates could be seen. Cutting the tree down a, very past it, Pressed steel Frances Barnett collapsed with the tree. Only the Villiers engine/gear box was salvageable. A 250 Royal Enfield was only slightly better, as the engine and frame were re useable. All the tinware fell to bits. A NSU Quickly in similar state was next followed by a Triumph 500 Café Racer ,not to bad, as it had some good stuff on it. The bike in the middle, under a rotten tarpaulin was the winner, a 36 BSA Empire Star, rusty but sound and complete. I had to take the lot, as the couple selling had come from Austraila to clear the house. I agreed to pay more if we could find the Log Books, but no joy, she had thrown them out with lots of other paper work. I noticed two boxes on a table. Turned out to be two sets of cycle thread taps & dies, one normal right hand , the other set, Left Hand thread! They were in super condition, the L/H set looked unused. I offered £50 which was refused ,as she liked the “nice wooden boxes” I said you can keep the boxes, I will just have the contents for the £50 The Husband said “Yes”. The Wife said NO! The two sets went to Auz . Never seen a set like it before or since! Regards Geoff.

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