Cylinder Stud Thread Profile

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ogrilp400

Well Known and Active Forum User
Non-VOC Member
Dear All,
Has there been a consensus on exactly what thread form the cylinder stud thread is into the crankcase and nuts? Know Thy Beast says 9/16" x 20 Whitworth form. I seem to remember some years back that 9/16" x 20 Admiralty was deemed the correct one. On the engineering drawing it says 9/16" x 20 CEI. Professor Neville Higgins wrote in MPH 643 that there is a difference between CEI and BSCy that can cause problems. Can we please have a final definitive answer? Given that I am repairing this sort of thing I really would like to know what is correct.

Phelps.
 
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chankly bore

Well Known and Active Forum User
Non-VOC Member
I have "Engineering Workshop Data" published by Caxton (U.K.) in 1947. It is obviously coeval with the era of H.R.D./Vincent production.It refers to C.E.I.threads the standards of which were published in 1901 and re-issued as B.S.C. threads in B.S. 811 of 1938. It lists 9/16" x20 t.p.i. both right and left as an "exceptional thread" for bicycle pedal cranks. See M.P.H. 661 for an interesting article on the subject by Mike White. Laurie Binns ( bless his memory) used the special tap mentioned on a long registering shank together with 9/16 x16 U.N.F. inserts or 14mm. spark plug ditto. The bicycle world is quite literate about this thread. P'raps we can talk the excellent and erudite Magnetoman into some microphotography to lay this issue to a long-deserved rest.
 
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ogrilp400

Well Known and Active Forum User
Non-VOC Member
G'day Charlie,
I have used the long registering shank tap and also UNF and 14mm x 1.25 but the studs will not screw in. I also carried out a repair for a mates early Triumph forks which was also 9/16" x 20 and as Triumph used Cycle threads on a lot of their early bikes I deemed that to be CEI too but again too tight to get the original spindle in. I am now beginning to wonder if the helicoil tap supplied to me is under size.

Phelps.
 
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ogrilp400

Well Known and Active Forum User
Non-VOC Member
roy the mechanic said:
K T B, page 237 9/16x20 tpi 55degree thread angle.
Click to expand...
G'day Roy,
So why does the works drawing list it as 9/16 x 20 CEI and Prof Higgins article saying there is a difference between CEI and BSCy ?
 

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Peter Holmes

Well Known and Active Forum User
VOC Member
We have original factory crankcases, we have had DRAT crankcases, we have Molnar crankcases, we have Wyatt crankcases, we have Godet crankcases, then we have the Spares Club making/supplying ET55/2 along with other specialist parts manufacturers/suppliers, surely someone can give us a definitive answer, please!
 
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