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Are the B31 and B33 transmissions the same or are there differences? What are the differences? Do these transmissions share any parts, other than small incidental parts? I am interested in shafts and bushings. Any info will be appreciated.


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The B31 and B33 are B group so used the same gearbox, the gearbox used is determined by the frame ie plunger Swingarm etc.

https://draganfly.co.uk/product-cat...133/engine-gaskets-gearbox/gearbox-abcm/

There will be differences on what sprockets used but shafts and bushings will be identical as long as the gearbox matches the frame.

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Thanks. The bike is a 54 B31 Goldstar clone. CB32 bottom end, DBD34 top end, modern AMAL carb. Belongs to my son. The bike starts in 2 or 3 kicks cold. He has not quite got the handle on starting it when hot. We are having trans/clutch issues.


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Do the A series and B series transmissions share any common shafts?


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The swing arm A and B transmissions share most parts.

Why do you think you need shafts?


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Note there are shafts for bushed gearboxes and needle roller boxes, they differ by thou,s on diameter.

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Just to confuse things further, there were a number of variations of the pre-unit swinging arm A (twin) and B (sngle) gearboxes.

The most common is the STD (standard) which was fitted to most road bikes. There were also TRI (trials) and SC (scrambles), then we get into the competition variations which used needle roller bearing instead of bushes. T indicates Torrington needle roller bearings on the layshaft (eg STD.T and SC.T), and T2 indicates there was also a needle roller bearing in the mainshaft sleeve gear (eg SC.T2, RR.T2)
Last but not least, there was a reverse campmate available, mostly used on Gold Stars. which reversed the gear change pattern.

Depending on how Gold Star-ised the bike is, it might have any of these, or a bit of a mix of parts.

BSA service sheet 302B lists the gear ratios and parts for the swinging arm A & B group gearboxes. There is a copy at [url=https://www.a7a10.net/forum/index.php?topic=2717.0][/url]

It's also available, along with lots of other very useful information on Lim the CD Man's BSA DVD.

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Originally Posted by Mike Lydon
We are having trans/clutch issues.
The 6-spring clutch can be quite fussy to set up correctly.

Most gear selection problems tend to be related to either selector wear (most likely the campmate) or shimming.

Bush wear is quite common as well, but often isn't obvious. It's not unusual to dismantle a gearbox which seemed to be working "alright" and find the bushes are beyond their wear limits.
These old things are very mechanically forgiving.

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At a stop, it felt like it popped out of gear, but was actually stuck in third gear. My son nursed it home. He said it was just as much fun as you think it would be. Took it to a recommended Brit bike mechanic who determined (?) that the layshaft was bad due to its bushings being worn out. He said the bushings were NLA, made a set up in his lathe. He said the layshaft was also NLA, so used shaft from an A series box, as they were the same. He apparently didn't check the gearbox/clutch function before returning the bike to my son. When the clutch lever is pulled, there is no clutch movement. I just feels like you are trying to stretch the cable. We called the mechanic and he said it was just a clutch adjustment. I tried adjusting the clutch on the primary side. The only way I could get clutch lever movement was to back out the clutch screws almost all the way out. My son freaked out and would not let me do anything further. This bike is not going back to the mechanic. So, just trying to determine if the problem is a simple clutch adjustment, or if the shaft is NOT the same, and ay be a little too long.


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Where were you trying to adjust the clutch from ?
Aside for the wrong place there is a ball bearing that has a habbit of leaving which then makes the pushrod too short
Do as others have suggested & downoad the clutch & gearbox diagrams


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Originally Posted by Mike Lydon
Took it to a recommended Brit bike mechanic who determined (?) that the layshaft was bad due to its bushings being worn out. He said the bushings were NLA, made a set up in his lathe. He said the layshaft was also NLA, so used shaft from an A series box, as they were the same.
Hmm, the layshaft bushes (67-3230 and 67-3099) are quite readily available. The bushed layshaft (42-3019) is available, but not cheap. Yes, they are interchangeable,

Originally Posted by Mike Lydon
He apparently didn't check the gearbox/clutch function before returning the bike to my son. When the clutch lever is pulled, there is no clutch movement. I just feels like you are trying to stretch the cable. We called the mechanic and he said it was just a clutch adjustment. I tried adjusting the clutch on the primary side. The only way I could get clutch lever movement was to back out the clutch screws almost all the way out.
The later 4-spring and 3-spring clutches have an adjustment screw and lock-nut in the centre, but the 6-spring doesn't. The 6 nuts are to adjust the clutch spring tension and ensure the pressure plate lifts squarely. What lift adjustment there is, is at the lever at the other end of the pushrod, hidden behind the inspection cover.
Service Sheet 308 (but there were a number of re-issues) covers dismantling and reassembling the clutch, 310 covers clutch adjustment, chain alignment, etc, and 311 covers dismantling and reassembling the gearbox. 310 and 311 are available from bsa-info.nz

Originally Posted by Mike Lydon
This bike is not going back to the mechanic.
That seems wise smile

Originally Posted by Mike Lydon
So, just trying to determine if the problem is a simple clutch adjustment, or if the shaft is NOT the same, and ay be a little too long.
The clutch pushrod runs through the centre of the mainshaft, so it won't be that. My guess is that the clutch was adjusted incorrectly, or the clutch arm assembly was 1 spline off.

A lot of the BSA service sheets and manuals are now available online, but it can be a hassle to know which you need. I bought my copy of Kim's DVD long before much was available online, and it still comes in handy.

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Thanks for all the info. This info will be very useful.


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