Gearbox ratios

[redhunter]

I have a 1948 A7 with a sidecar to restore.
Reading a 1948 advert for the A7 it implies that there were two gearbox options, one of which was for side  car use. Can anyone tell me if i can identify a sidecar gear box from the serial number on the gearbox?

[bsa-bill]

I'd be interested to hear from those with early As who will know if I'm wrong but all the ones I know of have a choice of gearing for sidecars, this only involves changing an external gear (engine or gearbox) to lower the overall gearing, gearbox remains the same.
There are different gear ranges ( scramble, road, racing ) that are fitted to the same gearbox, the box is then (if factory fitted) stamped with the ratio code and there is also a RTT2 box that is internally different in having needle bearings in place of bush's.
I think I'm safe in saying though that for general sidecar work only an external gear needs to be changed

[gavinoz]

When I got my rigid, they said it was geared for sidecar by way of a larger final (rear wheel) sprocket, and the other sprockets were same as solo. It certainly felt that way. Acceleration was great but top speed was low. gav. 

[Brian]

As far as I know there where no alternative ratio gearboxes available for the rigid/plunger gearboxes. For sidecar use the rear sprocket was changed from a 46t to a 49t.

[Stephen Foster]

My longstroke "Star Twin" is fitted with a close ratio gearbox (marked C.R) .. I believe this to be its original fitment .
Does anyone have any information on this gearbox please ?

Steve ..

[trevinoz]

Steve,
                 Have you actually checked the ratios? Like Brian, I haven't heard of any alternative ratios for the bolt-up box.
Where is the "CR" stamped?

Trev.

[wilko]

Put some air in that front tyre too!

[Stephen Foster]

I havent checked the ratios .
The C R is stamped in the normal area near the clutch arm .

This is the stamp & the order it appears          W X .

                                                                          C R .

I imagine the W.X is an inspectors mark ?
The marks are as above one higher than the other .