Author Topic: Which gearbox sprocket?  (Read 304 times)

Offline Russ

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Which gearbox sprocket?
« on: 20.03. 2019 12:25 »
The gearbox which came with my 51 A10 Plunger had an 18 tooth sprocket fitted. It is an old original sprocket with the scroll on the collar. The size of the spline on the shaft is 11/32. 
Draganfly's site shows  Part # 67-3051 was an 18 tooth for 48 - 49, Part # 67-3064 was an 18 tooth for A7, 50 to 57 and A10, 54 to 57.
Part # 67-3065 is a 19 tooth sprocket for A10, 50 to 53 which is the one I need.
However, when researching I find that "Feked" state their sprocket is 5/16 NOT 1/4. I am now confused!!!
My question is, will the 19 tooth sprocket part # 67-3065 fit my gearbox shaft with the 11/32 spline?

Thanks Russ
1951 A10 Plunger.
Australia

Online duTch

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Re: Which gearbox sprocket?
« Reply #1 on: 20.03. 2019 12:59 »

 I can't think any reason why it shouldn't fit....I assume that the 11/32" is the width of your splines but can't comment on that, and I guess the 5/16" is the width of the sprocket which sounds right- I think the pitch is maybe 5/8"  *doubt*.... The box I'm using came with a scrolled sprocket and I replaced it with a seal type item with no problems (apart from me being me)
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
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Offline Swarfcut

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Re: Which gearbox sprocket?
« Reply #2 on: 20.03. 2019 14:37 »
Russ   If your bike is an A10 with an 18 tooth gearbox sprocket, it is either originally an A7 solo box or an A10  set up at some stage for sidecar work.

 The boxes are the same inside, they have the same gears, but the  rear sprocket would be 46 for an A7 solo, 49 for sidecar work.  Standard gearing for an A10 is a 19 tooth gearbox sprocket, rear sprocket 42 teeth (solo) or 49 teeth (sidecar). However, owners could mix'n match because all the bits interchange.

 The good news is that all these gearbox sprockets have the same spline, which is also common to the later Swing Arm box.  These days 20 and 21 tooth gearbox sprockets are available for more relaxed less frantic cruising.

 The scroll was changed to a seal sometime in 1951, this is the difference in your quoted A7 part numbers. All new sprockets are of the seal type, so you will need to fit the later seal, which is easily available and again common to all A series boxes, Plunger and S/A.

 Like duTch says, the  5/16" refers to the width of the teeth, in other words wide enough to fit the gap between the sideplates of the chain, with a little bit of clearance.   The rear chain size is known as  5/8" x 3/8", pitch x width.    Other machines in the BSA range have sprockets with the same number of teeth, but use a narrower chain, which is a bit puny for the high power output of a well sorted A.

 So, the answer is that a 19 tooth sprocket  67 3065 plus gearbox sprocket  seal 67 3067 is what you need. The seal retaining ring is the same for all boxes, 67 3026, if you need a new one.

 

 Swarfy.

Offline Russ

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Re: Which gearbox sprocket?
« Reply #3 on: 20.03. 2019 21:50 »
Dutch and Swarfy thankyou for your excellent replies.  My gearbox has been rebuilt with a new seal so I can now confidently buy a new 19 tooth sprocket to suit.
Cheers Russ
1951 A10 Plunger.
Australia

Online Brian

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Re: Which gearbox sprocket?
« Reply #4 on: 21.03. 2019 02:16 »
Try and help a little here if possible.

A chain that is 1/4" is a 520 chain, 5/16" is 525 and 3/8" is 530. All these chains are the same pitch, thats the distance between pins.

The A10 uses a 530 chain but you have to be careful with the plunger models that the chain is not too wide, you can not use a modern heavy duty 530 chain on a plunger A10. A chain that is too wide will gouge alloy out of the gearbox and back of the primary case. If you can find one a Reynolds chain is good as they are quite thin, a modern std duty chain is usually ok.

The 1/4" or 520 sprockets were used on the B31/33 models, the sprockets will interchange but the widths are different.



Offline Russ

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Re: Which gearbox sprocket?
« Reply #5 on: 21.03. 2019 05:20 »
Thanks Brian, I have added that information to my file.

Russ
1951 A10 Plunger.
Australia

Offline Rocket Racer

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Re: Which gearbox sprocket?
« Reply #6 on: 09.04. 2019 06:22 »
on my race a10 (sidecar), I run 520 sprockets and chain and have had no wear issues.
if replacing both sprockets a good idea worth consideration.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline muskrat

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Re: Which gearbox sprocket?
« Reply #7 on: 09.04. 2019 09:44 »
G'day RR.
That's a good conversion. The 520 chains of today are more than up to the mammoth pony power of out A's. Stronger, lighter and sap less power to run. I have 520 on the cafe with an alloy rear sprocket.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Online Beeza

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Re: Which gearbox sprocket?
« Reply #8 on: 11.04. 2019 08:54 »
Hey Rus, there's a motorcycle only swap meet and show near you at Mirboo North this Saturday  (13/4/19) 8:00. Cob (Pete) Smith, will be there with all his swap meet stuff, he has a selection of BSA parts and a large selection of repo parts. It would be a good day out also.
I will be going also.
BTW do you still have the 276 carb (for sale).

Cheers Thomas