Author Topic: Gearbox sprocket  (Read 1226 times)

Offline RoyC

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Gearbox sprocket
« on: 01.07. 2017 16:31 »
Having trouble finding 67-3068 gearbox sprocket 17 teeth.
I have found this one, but will it fit http://www.ebay.co.uk/itm/GS92480-GEARBOX-SPROCKET-BSA-Triumph-for-C25-B25-B44-B50-17T-OEM-41-3092-/321647352360?hash=item4ae3ad1a28:g:unsAAOSwMmBVriDr ?
Roy.
My bike is a 1958 A7SS
Staffordshire UK

Online JulianS

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Re: Gearbox sprocket
« Reply #1 on: 01.07. 2017 17:19 »
That wont fit. The unit single takes a 5/8 x 1/4 chain and your A7 takes a 5/16 x 3/8.

Try any of the big dealers should not be a problem finding one.

Offline duTch

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Re: Gearbox sprocket
« Reply #2 on: 01.07. 2017 17:22 »

 Why a 17T ? If you want to change the gearing, I reckon going bigger on the rear is better
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Online JulianS

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Re: Gearbox sprocket
« Reply #3 on: 01.07. 2017 17:54 »

 Why a 17T ? If you want to change the gearing, I reckon going bigger on the rear is better

Only one other opition on the full width iron hub - the 43 tooth rear for the sidecar A50 .

Offline RoyC

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Re: Gearbox sprocket
« Reply #4 on: 01.07. 2017 18:20 »
Yes, it is for a sidecar.
I will have a hunt round for a 43 tooth rear.
It should be a much easier change as well.
Thank you both for the solution.
My bike is a 1958 A7SS
Staffordshire UK

Offline RoyC

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Re: Gearbox sprocket
« Reply #5 on: 01.07. 2017 18:37 »
It looks like there is no such item as a 43 tooth rear sprocket to fit my hub.  *sad2*
My bike is a 1958 A7SS
Staffordshire UK

Online JulianS

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Re: Gearbox sprocket
« Reply #6 on: 01.07. 2017 20:02 »
Part 68 6034. For A50 with full width iron hub sidecar use. 43 teeth.

A change from solo to sidecar gearing when gearbox or rear wheel are changed does affect the accuracy of the speedo.

Online JulianS

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Re: Gearbox sprocket
« Reply #7 on: 01.07. 2017 20:54 »
Roy

Have you considered changing the engine sprocket - a 16 tooth one would give similar gearing to changing the gearbox sprocket to 17 tooth one.

They seem to be available.

Offline RoyC

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Re: Gearbox sprocket
« Reply #8 on: 02.07. 2017 08:57 »
Roy

Have you considered changing the engine sprocket - a 16 tooth one would give similar gearing to changing the gearbox sprocket to 17 tooth one.

They seem to be available.

Thanks Julian.
The parts catalogue only lists numbers for 18T & 21T engine sprocket.
The 43T rear chain sprocket is unavailable.
So I have had to go the 17T gearbox rout, I managed to locate one from British Bike Bits for £40-74 with P+P.
I know its going to be a BIG JOB for me to fit it as I don't even know where it's located.
Thanks to all for the help.
Roy.
My bike is a 1958 A7SS
Staffordshire UK

Offline duTch

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Re: Gearbox sprocket
« Reply #9 on: 02.07. 2017 09:17 »

 
Quote
I know its going to be a BIG JOB for me to fit it as I don't even know where it's located.

 Not a major surgery but not something you'd want to do often, and same for whatever G'box sprocket, just need to remove clutch and inner cover.
 The reason I suggest the 19T g'box and bigger wheel sprocket is the chain/sprocket travel, in theory should last longer for same overall gearing.

 If you use a 17T drive sprocket, what wheel sprocket do you have ?  A 19/43T doesn't sound like a lot of difference, I thought on at least Plungies they went from 18/47T (slight difference in Primary ratio).

 A65/50 '65-'70 used a 47T bolt on sprocket-band that would be readily available if you don't mind doing some adapting ?

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline RoyC

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Re: Gearbox sprocket
« Reply #10 on: 02.07. 2017 09:30 »

 
Quote
I know its going to be a BIG JOB for me to fit it as I don't even know where it's located.

 Not a major surgery but not something you'd want to do often, and same for whatever G'box sprocket, just need to remove clutch and inner cover.
 The reason I suggest the 19T g'box and bigger wheel sprocket is the chain/sprocket travel, in theory should last longer for same overall gearing.

 If you use a 17T drive sprocket, what wheel sprocket do you have ?  A 19/43T doesn't sound like a lot of difference, I thought on at least Plungies they went from 18/47T (slight difference in Primary ratio).

 A65/50 '65-'70 used a 47T bolt on sprocket-band that would be readily available if you don't mind doing some adapting ?

The reason that I have gone 17T gearbox is because that is what BSA did for sidecar.
I would prefer to go with the 16T engine sprocket but I can't find one.
There is also, as Julian pointed out, the speedo to sort out too.
Roy.
My bike is a 1958 A7SS
Staffordshire UK

Online JulianS

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Re: Gearbox sprocket
« Reply #11 on: 02.07. 2017 09:47 »
Going the gearbox route means removal of primary chaincase and clutch to access it. A bit more work if you have a fully enclosed rear chain.

There is a nice photo of the gearbox sprocket in post from Coater87 under "Lock washer"

There are NOS 16 tooth engine sprockets on E bay at moment

http://www.ebay.co.uk/itm/NEW-GENUINE-BSA-2-LOBE-CUSH-DRIVE-16T-ENGINE-SPROCKET-A10-A7-PRE-65-TRIALS/322227628312?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

They were available with 16 - 24 teeth and common to pre unit B series and Gold Star as well as A7 A10.

Offline RoyC

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Re: Gearbox sprocket
« Reply #12 on: 02.07. 2017 10:27 »
Going the gearbox route means removal of primary chaincase and clutch to access it. A bit more work if you have a fully enclosed rear chain.

There is a nice photo of the gearbox sprocket in post from Coater87 under "Lock washer"

There are NOS 16 tooth engine sprockets on E bay at moment

http://www.ebay.co.uk/itm/NEW-GENUINE-BSA-2-LOBE-CUSH-DRIVE-16T-ENGINE-SPROCKET-A10-A7-PRE-65-TRIALS/322227628312?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

They were available with 16 - 24 teeth and common to pre unit B series and Gold Star as well as A7 A10.

Julian, thanks for that link. I have just purchased one.  ;)
I think, for me it will be easier to change than the gearbox sprocket.
Roy.
P.S. I do have a fully enclosed rear chain.
My bike is a 1958 A7SS
Staffordshire UK

Offline RoyC

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Re: Gearbox sprocket
« Reply #13 on: 02.07. 2017 12:37 »
Is there anything else I am likely to need before I start taking the cover off ? (other than a primary gasket)
thanks for all the help.
Roy.
My bike is a 1958 A7SS
Staffordshire UK

Offline coater87

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Re: Gearbox sprocket
« Reply #14 on: 02.07. 2017 13:31 »
 Hi Roy.

 A decent way to remove the cush drive nut, and install it to 65 pounds.

 I would pick up a shim set for the engine sprocket if you dont have one. Might not need any, might need them all.

Lee
Central Wisconsin in the U.S.