The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: RoyC on 01.07. 2017 16:31
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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.
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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.
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Why a 17T ? If you want to change the gearing, I reckon going bigger on the rear is better
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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 .
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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.
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It looks like there is no such item as a 43 tooth rear sprocket to fit my hub. *sad2*
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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.
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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.
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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.
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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 ?
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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.
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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.
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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.
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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.
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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
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Hi, Roy
Have you tried the bike with the sidecar before changing the gearing?
I have found that certainly A10's are under geared on standard 1950's gearing
I am running +2 teeth on standard on the crank
Traffic moves a lot faster nowadays *ex* *ex*
John
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The cush drive nuts need to be very tight or they damage the chaincase if they unscrew.
You may find yours has been carefully tightened with a hammer and drift and if so may need similar tools to undo it.
If the nut is good you can use a Citreon ball joint socket to undo it - it fits a treat on a new nut - but you need a 35 mm spanner to fit the tool. I sent details to The Star the BSAOC magazine last year and it featured in the march 2016 issue.
You find the tool on ebay.
SRM do a hex replacement nut.
There is a lock washer but it is difficult to bend it up due to the cush spring and I always use thread locker.
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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
Thanks Lee.
Shim set ordered.
Roy.
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Our Gold Flash combo ran on standard gearing for years with a child/adult sidecar, usually full of 2 fighting brats plus paraphernalia. I'm pleased to say the 2 fighting brats are now respectable parents with their own fighting brats and the Gold Flash is liberated as a solo. So try it first and see.
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Hi, Roy
Have you tried the bike with the sidecar before changing the gearing?
I have found that certainly A10's are under geared on standard 1950's gearing
I am running +2 teeth on standard on the crank
Traffic moves a lot faster nowadays *ex* *ex*
John
Hi John
I haven't even ridden the bike yet.
I am having the sidecar made by Watsonian-Squire.
Similar to this one.
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Our Gold Flash combo ran on standard gearing for years with a child/adult sidecar, usually full of 2 fighting brats plus paraphernalia. I'm pleased to say the 2 fighting brats are now respectable parents with their own fighting brats and the Gold Flash is liberated as a solo. So try it first and see.
I will.
At least I will have the gear to do the job if required.
Thanks for that.
Roy.
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The cush drive nuts need to be very tight or they damage the chaincase if they unscrew.
You may find yours has been carefully tightened with a hammer and drift and if so may need similar tools to undo it.
If the nut is good you can use a Citreon ball joint socket to undo it - it fits a treat on a new nut - but you need a 35 mm spanner to fit the tool. I sent details to The Star the BSAOC magazine last year and it featured in the march 2016 issue.
You find the tool on ebay.
SRM do a hex replacement nut.
There is a lock washer but it is difficult to bend it up due to the cush spring and I always use thread locker.
Thanks for that. Even if I end up not having to do it, I will know how to. *beer*
This is my gear at the moment.
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Hi Roy
If you have the primary cover off its well worthwhile to check that the cushdrive nut is fully tightened
If left otherwise it will lead to crank shim failure *warn*
John
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Roy
Doing any work on the left side of a sidecar equiped bike is quite challenging due to the confined space between bike and chair.
You need to be completely happy with the condition of the sprockets chains and the clutch and with the gearing before the chair is fitted because getting at it afterwards will be difficult.
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Roy
Doing any work on the left side of a sidecar equiped bike is quite challenging due to the confined space between bike and chair.
You need to be completely happy with the condition of the sprockets chains and the clutch and with the gearing before the chair is fitted because getting at it afterwards will be difficult.
Thanks Julian,
If I have to do any work on the bike when sidecar is fitted I will have to take the chair off so that I can get the bike on the lift.
Not room to get combo on the lift. *sad2*