Author Topic: Gearbox ratios  (Read 1387 times)

redhunter

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Gearbox ratios
« on: 25.04. 2013 10:18 »
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?

Online bsa-bill

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Re: Gearbox ratios
« Reply #1 on: 25.04. 2013 11:01 »
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
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline gavinoz

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Re: Gearbox ratios
« Reply #2 on: 25.04. 2013 11:10 »
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. 
Rigid A7S, 57 A10 in pieces
Australia

Online Brian

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Re: Gearbox ratios
« Reply #3 on: 25.04. 2013 13:07 »
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.

Offline Stephen Foster

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Re: Gearbox ratios
« Reply #4 on: 04.05. 2014 07:35 »
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 ..
I own a 1955/56 B.S.A Swinging Arm "Golden Flash" , had it since 1976 .

Offline trevinoz

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Re: Gearbox ratios
« Reply #5 on: 04.05. 2014 22:04 »
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.

Offline wilko

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Re: Gearbox ratios
« Reply #6 on: 05.05. 2014 00:00 »
Put some air in that front tyre too!

Offline Stephen Foster

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Re: Gearbox ratios
« Reply #7 on: 05.05. 2014 09:10 »
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 .
I own a 1955/56 B.S.A Swinging Arm "Golden Flash" , had it since 1976 .