Author Topic: A10 gearbox clutch mainshaft thread size?  (Read 209 times)

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rogereld

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A10 gearbox clutch mainshaft thread size?
« on: 16 March, 2019, 13:44:14 »
What is the thread size and type for the clutch mainshaft nut on a 1959 A10 s/a?

 I am changing my clutch from the original 6 spring to a new 4 spring, and the new clutch mainshaft nut I have been supplied does not fit smoothly on the gearbox mainshaft. It is the right size (5/8") and 20tpi. Part number 42-3267. My helpful local supplier has run a 5/8 x 20tpi CEI tap through the nut in an attempt to improve the fit but it is still very tight on the mainshaft. The original 6 spring mainshaft nut turns on easily by hand but can not be used with the 4 spring clutch. I have tried several new hub nuts at the parts shop, on a spare gearbox mainshaft, for both 6 spring and 4 spring clutches, and they are all very tight so I suspect the pattern parts have not been cut with the same thread as the original parts.  Is the gearbox mainshaft thread something different or unusual, and possibly not a CEI thread? 

Bess

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #1 on: 16 March, 2019, 14:12:36 »
Hi,
     My records show a 42-3267 as 5/8" 20 tpi. I had a similar problem on an A65, the zinc plating in the nut needed a tap to open the threads and a thread file on the end of shaft to straighten out distorted threads. It maybe worth investing in a set of threads gauges to check.

https://www.ebay.co.uk/itm/2-Pcs-Stainless-Steel-Metric-Screw-Pitch-60-55-Degree-Thread-Measuring-Gauge-CS/273354108481?hash=item3fa52cae41&enc=AQADAAADAFjVrDbVsZ8oH%2F8PNHtt9VX4%2Fw7FZcmMuqsX8uaFEduVuhcrsbuFHqaE4qgP8QZ9K5uyNG%2BxkHaUTl6KkbmyKEWMS3DbEH8TXsWzwmWRzivF%2FPpPf2YgEBv%2BLFbav%2B%2BLpHUbPQ7GTdlPGMybLe3J%2F1J0SgYNNrIEVBgU3rzfqbObdUJ3n2owUrN2TP4DmfelSFoiPUIPCUyQgqY4IVGs6FvZ7%2FBowqmMUOB%2Byj4t0NFEFKbzy9e7o3SvNoiz%2Bj7yvq6P34X%2BYfy7NkYD4fo0%2FQbksgCYMSOCDP%2BqFVej9sgmtZ5oUF7zJIHpKcg8UpexICfg7M4yJNsT%2BFCtl4IZvnyc8jDegE21ysoxGCWDyK1J%2B6KSMMuWHnMdOhe3VneKPKUYP3qYlnSGt1I3ml6bIiYDKZOiOOK1t747vJxK6D1hePFHDHL61enjM8K7srA2rJURlkq58yfbxjmpkXjpe3gKxR0s3wwBJTIVswjyu5XPN8Jm0FOhWdeC%2BZwpqGBGfnMuuTZKs%2F%2Fv2JCJDP4nw87aIM3LX2OfAfgdyUP3yhUnp%2FKKz9koqGYH2iZzaa1Qtu9hezvzCgrk3WDXJIS6pXzA3CWoa%2FS46THX8dKCAyCo0yzUnizzPXjLCSeVM8t59OO2uWdvm1KUYWC4oQWybWXETE%2BZB%2BcB4fhLN%2FrZ0k4WubYdTNm35m3ARMmrucjrLmW%2F2lns7IelQvtJVVKMpUoH1nyp%2Fdfegyov5OogWQlcsbToxwHI0AV2JBragA6Dp2DFwlMxFPQfxm5RjTY4xH4gp0%2F%2BF9BbWHEfuez5eUS9z3erldIDkNhq3ANyVqO8b8SGlnQhBPm6LUxQm7uihtelsd1gN0Xapvy6yvOyLKTJ3WtGj76fxH9Ubt9KrgnpuJovsvLsDdzhRle%2BbDwA82B4OqxWIW7LUYwOA%2F6sxP1qxYgJbJ451kph%2FHfw6D7uzYpI9PiTSNdl%2BdwzAeHvhpCx%2B5NWjCj%2FV15H83KDgam%2BBuU4NsPnJHD7PNb9PDF8cA%3D%3D&checksum=27335410848149144491f36a438f88e5b6c5feda2cf5

Best wishes...

rogereld

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #2 on: 16 March, 2019, 14:43:42 »
Thanks.  I had got the 5/8 and 20 tpi bit, but is it CEI, or Admiralty thread, (or something else) and how different are the different thread types.  I have been in the parts shop this morning and a 5/8 20 tpi CEI tap has been worked through the thread in an attempt to make it fit but it still does not fit correctly.  My gearbox mainshaft accepts the original 6 spring hub nut which spins on by hand so I do not think my gearbox shaft has any thread damage, but the new nut is stiff even with the use of a 12" long ring spanner and that is after cleaning out the thread with the tap.


Bess

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #3 on: 16 March, 2019, 17:27:49 »
Hi,
    The 5/8" CEI is a 60 degree thread, depth 0.533 x pitch, an Admiralty is a whitworth fine at 55 degrees, depth 0.64 x pitch both at 20 tpi, very unlikely to be Admiralty thread.

It still seems to me that the shaft has distorted threads that need attention, try the tap in the old nut and you might find it bites. Also try aligning the tap along the shaft threads looking for problems. The links below demonstrates that the threads are the same for both nuts:

https://www.britishbikebits.com/gearbox-mainshaft-nut-bsa-a-b-m-models
https://www.britishbikebits.com/clutch-mainshaft-nut-bsa-a7-a10-1959-63

Best wishes...

« Last Edit: 16 March, 2019, 17:48:09 by Bess »

rogereld

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #4 on: 16 March, 2019, 18:27:02 »
The two links to britishbikebits both state that new pattern parts are being made with a thread of 5/8"  20 tpi.  That agrees with the stock my local supplier has. But the stock at my local supplier does not fit correctly on the gearbox mainshaft that my local supplier has in his shop, and they do not fit on my mainshaft. If it was only my mainshaft that had problems accepting the nut, I would be looking closely at the thread on my mainshaft, but to have the same problem on a different mainshaft, and I have spoken this afternoon to another A10 owner who had similar problems with the nut not fitting on his mainshaft, I suspect the new nuts are not being manufactured with the same thread as the originals.

To add confusion, the factory list of all BSA thread sizes quotes the 4 spring mainshaft nut, part number 42-3267 as: " Nut, CEI, 9/16 - 20, Mainshaft A10 4 spring mdls."  That suggests a 9/16" thread size.
The 6 spring nut is quoted as: 66-3787, Nut, ???, ???, Mainshaft B31 B32 B33 B34. (The size and thread pitch are not given.)

If the Admiralty thread is the same tpi but cut a bit deeper than CEI would that make the fit of the nut on the shaft a bit looser than if it is CEI? That would solve the problem. At the moment the nut appears to have the correct tpi but is just very tight.



JulianS

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #6 on: 16 March, 2019, 19:35:24 »
The A10 gearbox mainshaft thread is 5/8 x 20 tpi BS cycle.

The A65 used a 9/16 x 20 tpi.

BSA did not use Admiralty threads on the A10.

I think you need to source another nut but from a different source.

It is possible that the new nut is wrongly made - how close would a 16mm x 1.25 thread appear to the 5/8 x 20 tpi?

chaz

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #7 on: 17 March, 2019, 09:13:51 »
its a common problem with any parts being remanufactured today. I cherry picked all our best taps and dies before they got thrown out.. All we do now is Metric standard with the odd metric fine and British Standard Pipe  BSP. due to availability parts are being offered to us as a guess by many NEW or FOREIGN suppliers. an example Ariel Square 4 have a large nut set in a recessed washer, the correct A/F hexagon will accept the correct socket in the recess, metric hexagon, the socket only sits on the top and drives half of the hexagon.
I might guess the 5/8 x 20 BSC is correct .
 problem being is some parts were made for US market around this time and came in as UNEF Unified National EXTRA Fine. or some UNS Unified National SPECIAL.
a common problem it seems

https://www.accessnorton.com/NortonCommando/bsc-cei-uns-and-other-thread-stuff.16815/

rogereld

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #8 on: 17 March, 2019, 09:30:01 »
I have found several online listings (eg Classicbikeshop) that list a Triumph/BSA 4 speed clutch centre nut (eg part No 57-1047, 57-0421, or 68-3030) that looks identical but has a thread size of 9/16". The A65 gearbox mainshaft is cut with a 9/16 20 tpi thread so these nuts will fit correctly on A65 and other later model BSA's using the 4 spring clutch.

Part number 42-3267 clutch centre nut has a thread of 5/8" 20 tpi and is not the same as the part numbers listed above.

If I have been supplied with a 9/16" 20 tpi thread nut would it start to go on a 5/8" shaft, and feel extremely tight?

Both nuts are listed for use with the 4 spring clutch but I have not yet found a supplier who has stock of both thread sizes, 5/8" needed for the A10, when converting from 6 spring to 4 spring, and 9/16" needed for the gearbox mainshaft on later models.



« Last Edit: 17 March, 2019, 09:31:37 by rogereld »

Bess

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« Last Edit: 17 March, 2019, 10:09:40 by Bess »

rogereld

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #10 on: 17 March, 2019, 10:44:33 »
I have found a number of places that list the clutch hub nut using the part number I need, but I have not found anywhere that lists BOTH. 5/8 and 9/16 thread.  If I found a supplier that listed both that would suggest they are aware of the difference, and I would be more confident I was ordering the correct item.


rogereld

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #12 on: 17 March, 2019, 13:46:27 »
Thank you for finding the website links.   I had previously tried putting the part numbers in the SRM website search box and found nothing, but I think I was using a dash after the first two digits as common with most other BSA parts listings. A close look at the SRM listings shows SRM use a dot instead of a dash.

Neither SRM or Feked give any details of the thread sizes so I will phone them to check before ordering.

chaz

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #13 on: 18 March, 2019, 09:05:21 »
you have to put your trust in the suppliers but as normal Caveat Emptor, Buyer beware.
A few years ago I ordered some bolts from a dealer 1/4BSW , didnt work, checked them and they were M6, a similar size but different thread angle. They will be ok , I was told on the phone.

rogereld

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Re: A10 gearbox clutch mainshaft thread size?
« Reply #14 on: 19 March, 2019, 11:52:30 »
I have obtained another clutch hub nut from another supplier. 5/8" size. It fits perfectly on to my gearbox mainshaft. Problem solved.