Gearbox 'A' Group (Swinging Arm) STD

[db133]

Hi

Would one of my learned friends please inform:

How many versions of the STD Group 'A' (Swinging Arm) Gearbox are there and what are the differences ?


Kind regards.

[BSA_54A10]

How long is a piece of string ?
You can make something like 30 different ratio boxes if you really want to.
AFIK ;-
BSA marketed a standard box.
3 close range boxes
2 wide ratio ratio boxes
1 special Daytona box

[db133]

How long is a piece of string ?
You can make something like 30 different ratio boxes if you really want to.
AFIK ;-
BSA marketed a standard box.
3 close range boxes
2 wide ratio ratio boxes
1 special Daytona box

Thats very interesting do you have any more details ?
 
I have found the BSA chart Gearbox ratios A&B Group S/A Models and the BSA service sheets.

Kind regards.

[Brian]

This one lists 17 different boxes.

[BSA_54A10]

The list shows only BSA recommended gear combinations.
You can do non recommended things like 3 really low close gear and 1 really high gear.
Or a low 1st , big jump to a close 2 & 3 then long jump to 4 for hilly road tracks with a long strait.
The possibilities are endless but some end up being really hard to change between 1 or more ratios
There are also other gears that can be used that are not on the list because BSA did not recommend them for A Series Twins.
You could build a different box for each and every track on the continential circuit which is one of the reasons why BSA did so well on the track with so little effort and as all the gears used were standard BSA gears the scrutineers could not dissallow them even if they were not a box that was available on the bike.
Just about every gear that BSA cut from 1910 to 1962 could be grafted into the A box as the splines & diameters were the same on nearly all of the shafts

[db133]

Thanks for the information. Mind boggling really.
I have been working from the BSA Service sheet No. 311. it has been a great help.
I would like to find more information on rebuilds and service etc if possible.

Kind regards

[BSA_54A10]

I pulled apart the box on my 1926 round tank and found that I could rebuild it with WM20 gears.
Ratios are not quite the same but it will do me fine as I can make a 3 speed very close ratio box to use the (lack) of power to it's best advantage.

[db133]

I have been trying to find some information on the acceptable tolerances of the Layshaft and the Bronze Layshaft Bushes #65-3337 and #67-3099 
Any information will be appreciated and if anyone knows someone who will make bespoke Layshaft bushes please let me know??..to be continued??Regards.

[chaterlea25]

Hi db133,
The service sheets no. 702 give a dimension of 0.687-.688in. after reaming and fitting to the cases
It is common to find the layshaft worn or scored or both
They can be turned or ground undersize to recover them,
I would install with about .002 in. clearance, (fitted)

Where are you situated? the forum members will know some capable people in your area
I know SRM do this repair, I can also do it but I am located in Southern Ireland
HTH
John O R

[db133]

Hi John

Thanks for the information much appreciated.

Ref :
"Where are you situated? the forum members will know some capable people in your area".

I'm in Brighton Sussex and looking for a good  Engineering firm in the area.............

Kind regards.