Help with Studs

clevtrev

Well Known and Active Forum User
VOC Member
Steve

9/16" 20 TPI taps available on ebay - RDG Tools.

I think this was a common thread in the 50s known as cycle thread and if memory serves me correctly it was 60 degrees.

One word of warning - the taps on ebay seem very cheap at £7 ish, but it may be a starting point - a cheap tap broken in the hole can be a real problem.

H
9/16"x 20 TPI CEI, is a whitworth form thread. See BS 811. As are all the 20 TPI series of CEI. ONLY the 26 TPI are 60 degree thread angle.
Are you using original studs ? that`s the first thing I would ask.
New castings, if not properly heat treated will have a tendency to close up a little after initial tapping. This could be a reason, as could using original studs.
 

clevtrev

Well Known and Active Forum User
VOC Member
Howard and Prosper, Thanks.

A friend of mine works on bicycles, and had a 9/16 20tpi tap. That happens to be the thread used on English crank pedals. I still don't know what the pressure angle is, but I chased the thread in one hole with it and my cylinder stud now screws in happily. I'll check the ebay vendor for a bottoming or 'plug' tap so I can be sure to get all the way to the bottom with it.

Aside from the 7/16 x20 and the 1/4 bsw that Prosper mentioned, are there any other extraordinary threads that spring to mind? Looks like I'll be ordering some taps and dies.

Thanks again.
5/16 "Whit. for the blind crankcase studs. 11/4"x 20 for the oil pump plug. 1/4 BSP for the drain plugs.
 

steve cassel

Forum User
Non-VOC Member
Cylinder Studs

ClevTrev, Thanks for weighing in on this. Looks like you've addressed and answered all of my questions.

Yes, my cylinder studs are original equipment. I was wondering how the tapped holes in the case could possibly end up too small... Perhaps the cases were hot when the threads were tapped? Also, are you saying that there are differences in cylinder studs? Are there 'reproduction' cylinder studs which are smaller than my original Vincent cylinder studs? I always imagined a more traditional sense of the word 'reproduction'.

At any rate, I'm happy to now have a good list of thread specifications for this motor. Time to order some more taps and dies. What a Great Hobby ;-).

-------Steve.
 

Howard

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VOC Member
9/16"x 20 TPI CEI, is a whitworth form thread. See BS 811. As are all the 20 TPI series of CEI. ONLY the 26 TPI are 60 degree thread angle.
Are you using original studs ? that`s the first thing I would ask.
New castings, if not properly heat treated will have a tendency to close up a little after initial tapping. This could be a reason, as could using original studs.

Trev

I think you'll find there are at least 2 different cycle threads, and there is definitely a 9/16" 20 TPI 60 degree thread version and a 55 degree version (according to my engineer's bible anyway - and that cost 17 shillings and 6 pence). I think the 60 degree is a later version, so a tap would probably be easier to get, but a 50s Vincent is probably 55 degrees as you state, so as I said (I think) measure twice and cut once.

Anyway, you've probably sussed the problem, so we won't argue over a mere 5 degrees.

H
 

clevtrev

Well Known and Active Forum User
VOC Member
ClevTrev, Thanks for weighing in on this. Looks like you've addressed and answered all of my questions.

Yes, my cylinder studs are original equipment. I was wondering how the tapped holes in the case could possibly end up too small... Perhaps the cases were hot when the threads were tapped? Also, are you saying that there are differences in cylinder studs? Are there 'reproduction' cylinder studs which are smaller than my original Vincent cylinder studs? I always imagined a more traditional sense of the word 'reproduction'.

At any rate, I'm happy to now have a good list of thread specifications for this motor. Time to order some more taps and dies. What a Great Hobby ;-).

-------Steve.
Your original studs, having the thread rolled on, will have a minor diameter larger than it should be. WHY ? because at the top end, if the thread were to be to standard, you would find the rolling over the top of the 1/2"BSF thread. So I imagine the factory to avoid this, kept the rolls a little light. To overcome this, the nut was made with a core hole to take this into consideration. So if you make sure that the hole in your case is 12.9/13mm, your stud will then screw in.
 

clevtrev

Well Known and Active Forum User
VOC Member
Trev

I think you'll find there are at least 2 different cycle threads, and there is definitely a 9/16" 20 TPI 60 degree thread version and a 55 degree version (according to my engineer's bible anyway - and that cost 17 shillings and 6 pence). I think the 60 degree is a later version, so a tap would probably be easier to get, but a 50s Vincent is probably 55 degrees as you state, so as I said (I think) measure twice and cut once.

Anyway, you've probably sussed the problem, so we won't argue over a mere 5 degrees.

H
As I said, read British Standard 811, and all will be revealed. I have.
 

Howard

Well Known and Active Forum User
VOC Member
9/16"x 20 TPI CEI, is a whitworth form thread. See BS 811. As are all the 20 TPI series of CEI. ONLY the 26 TPI are 60 degree thread angle.

Trev

Sorry, I don't keep obscure British standards. I'll have to gain solace in the fact that I'm not the only one who thinks there is a 9/16", 20 TPI, 60 degree cycle thread, I've even found companies in USA, India, Australia, China, Japan and Germany all making them to the wrong angle and all claiming they're made to BS811. To be honest it doesn't matter what BS811 says, companies are selling taps, dies and gauges claiming to be cycle threads that are 60 degrees. These include 3 British tool companies (web addresses below), put their 60 degree taps into a Vin crankcase to suit the 55 degree threaded studs (if that's what they are) and they wouldn't be a tight fit anymore.

H

http://www.coventrygauge.co.uk/pdf%20catalogue/Pages%20from%2010-11otherthread.pdf

http://www.tapdie.com/html/bscycle__taps.html

http://www.sizes.com/tools/thread_BSC.htm
 

steve cassel

Forum User
Non-VOC Member
Threads Threads Threads

Thanks, ClevTrev, for the explanation about the rolled threads. It took me a minute to follow what you were saying, but I get it now. Certainly, any reproduction cylinder studs are likely to be different than the originals. It's all starting to make sense. (Theme music from THE TWILIGHT ZONE is playing in the background).

Also, thanks Howard, for your encouragements and warnings. I did order many of those CHEAP taps and dies on ebay. I know they are not HSS, but I see that the vendor has excellent feedback, and I'm hoping the quality will be sufficient to my needs. I only need to use them to chase the existing threads clean... and I always use 'alumitap' fluid and cutting oils and try to work sensibly, so I'm expecting no problems (knock wood). Keep your fingers crossed for me.

It strikes me that since Vincents were created and assembled by craftsmen, we must learn much about those crafts to repair and restore them. As I said before... What a Great Hobby ;-).

-------Steve.
 
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