BSC, CEI, UNS and other thread stuff

Status
Not open for further replies.

B.Rad

Joined
Feb 28, 2012
Messages
287
Gidday All.
went to do up the nut holding on the clutch on mainshaft. Nut stuffed. grabbed a UNF nut. did not fit, wrong pitch. then measured mainshaft thread. 5/8th 20 TPI. it was the weekend. no chance to even think of purchasing one if even possible. So I made one and got out of trouble.

The question is : 1. what is this thread. I reckon 5/8th BSC. though 5/8th 20 TPI could even be UN constant pitch series, (5/8th 20 UN). I reckon both threads would be interchangable.
2. is the mainshaft thread the same on all AMC boxes ( Atlas etc) or was there some change when Commando's came out.
Given that Commandos used UN threads, this could be UN 5/8 x 20 or 5/8 x 20 BSC on Commandos.

it does not really matter but I am curious.

Just read the " stock fasteners " post. the circles on the stock fasteners indicate Unified thread form. This is an engineering designation, not exclusive to Norton.
all advice greatly appreciated.
Ride safe Bradley
 
Early Dommies (laydown box) and early AMC boxes used a 5/8" British Cycle Thread 20 tpi nut on the clutch,
so if Commando uses 20 tpi then it sounds it is the same nut.
(without having a Commando or Atlas one to conveniently measure).

5/8 UNF is 18 tpi....

A few fasteners/threads in the engine/gearbox never changed over the years,
from early dommie to late Commando.
Sounds like this is one of them.

Durned hard to find outside of your friendly Dealer with the green globe bags... ?
 
B.Rad said:
The question is : 1. what is this thread. I reckon 5/8th BSC. though 5/8th 20 TPI could even be UN constant pitch series, (5/8th 20 UN). I reckon both threads would be interchangable.
2. is the mainshaft thread the same on all AMC boxes ( Atlas etc) or was there some change when Commando's came out.
Given that Commandos used UN threads, this could be UN 5/8 x 20 or 5/8 x 20 BSC on Commandos.
Click to expand...

According to the parts books, Dominators, Atlas, etc. all had the same 040373 clutch retaining nut as Commando, so the thread appears to be 20 BSC/CEI.

Lock nut and washer to hold clutch to gearbox mainshaft. Suit all Nortons from 1934? to 1975.
Original Norton part numbers:
3331; A2/372; E6254; 040373 - main axle nut
Click to expand...
 
As A general rule all Cycle threads are 60degree thread form and 26 threads per inch irrespective of diameter. UNF is also 60 degree thread form and 20 tip is commonly found all over the place so looks like Norton used what they thought would suit when they changed from BSF, BSW and Cycle. BSF and BSW thread forms are 55 degrees. 1/4BSF happens to also be 26tpi and on a thread as small as that the form would probably not be an issue.
 
I have interchanged Atlas and Cdo clutch nuts on the Atlas AMC gearbox.

Slick
 
gripper said:
As A general rule all Cycle threads are 60degree thread form and 26 threads per inch irrespective of diameter.
Click to expand...

However, 20 TPI Cycle thread is also commonly found on motorcycles.

gripper said:
UNF is also 60 degree thread form and 20 tip is commonly found all over the place so looks like Norton used what they thought would suit when they changed from BSF, BSW and Cycle.
Click to expand...

5/8" UNF is 18 TPI and, as the nut part number was in use well before the Commando, there's really nothing to suggest that it's anything other than 20 TPI Cycle thread.
 
However, 20 TPI Cycle thread is also commonly found on motorcycles.
Click to expand...

20 TPI is listed as being an alternative to 26 TPI on diameters 7/16" and above, as its a rare thread I have used UNF and UNEF 20 TPI helicoil kits successfully.
 
Gidday All.
just want to say thankyou for all replies. it is much appreciated.

After carefully reading the posts, the mainshaft thread must be 5/8th Cycle 20 TPI. However for the American chaps in trouble 5/8 x 20 UNS will get u out of trouble. this assumes that 5/8 20 , being a special and American spec at that, is easier to get in America than here.
kommando said:

20 TPI is listed as being an alternative to 26 TPI on diameters 7/16" and above, as its a rare thread I have used UNF and UNEF 20 TPI helicoil kits successfully.
Click to expand...
Kommando, with the greatest of respect, if you order 5/8 UNEF you will get 24 TPI. 5/8 20 is UNS. the S designates a special. and even 20TPI is not a preferred thread in the constant pitch series. so u r right , it is rare. Enough of my pedantics. just trying to prevent the order of wrong taps or nuts for this purpose.

In summary, the mainshaft thread is 5/8 x 20 BSC. if not available in nuts, 5/8 20 UNS grade 5 or 8 will be fit for purpose.

Again, thanks for all replies. I have learned something from this.
Ride safe Bradley
 
I've just had a problem with the alternator nut on my BSA B44 - thread was very damaged. It too is 5/8 20tpi which as we know from earlier posts, is BSC/CEI. I managed to recut the thread by putting the crankshaft on a lathe and chasing the thread, and at the time I found that BSA bantam axle nuts are the same. There must be millions of the smelly little things around so if you are in urgent need of the correct nut - find a bantam aficionado. :wink:
 
Kommando, with the greatest of respect, if you order 5/8 UNEF
Click to expand...

Never suggested sizes at all just that there are some UNF and UNEF sizes that are 20 TPI and it means a easier way to get taps,dies and helicoil kits.
 
kommando said:
Kommando, with the greatest of respect, if you order 5/8 UNEF
Click to expand...

Never suggested sizes at all just that there are some UNF and UNEF sizes that are 20 TPI and it means a easier way to get taps,dies and helicoil kits.
Click to expand...

Kommando:: yes, I certainly read that wrong. as I said mate, with the greatest of respect.
Les, as I said mate, this subject of classification can be pedantic. I dont wish to be. The actual designation is UN Constant Thread Series. I cant carry all this stuff in me head, it hurts too much. gee I cant even quote common tapping sizes. I need to look this up. the ultimate reference here is Machinery's Handbook, 25th edition. pages 1637 to 1649.
Again thanks to all . fascinating to hear Bantams have this too. I learn a lot here.
Ride safe Bradley
 
In sunny England, we refer to 20TPI cycle thread as coarse cycle thread, just to prevent any confusion with the 'standard' variant which is 26TPI across all the diameters.

Boy, we really did confuse the world back in the good old days didn't we?!? Is it too late to apologise?

...or should that be apologize?
 
gtiller said:
In sunny England, we refer to 20TPI cycle thread as coarse cycle thread, just to prevent any confusion with the 'standard' variant which is 26TPI across all the diameters.

Boy, we really did confuse the world back in the good old days didn't we?!? Is it too late to apologise?

...or should that be apologize?
Click to expand...
No need for that ol China. Remember rods, roods, chains, perches, and of course Hyacinth Bucket.
Ride safe bradley
 
It may be worth remembering that the Commando chassis was eventually to be fitted with a more modern engine. Because of this all the chassis threads are Unified. This was being adopted by the entire British motor industry around the mid to late sixties. As the engine (Atlas) & gearbox were soon to be replaced it was decided not to update from Imperial thread forms i.e. BSW, BSF & BSC. Electrical items continued to use BA for a few more years.
Martyn.
 
"No need for that ol China. Remember rods, roods, chains, perches, and of course Hyacinth Bucket."

And how long is a perch? Does it depend on how old it was when it was caught? :D
 
Status
Not open for further replies.
Back
Top