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Primary drive sprocket #757447
11/28/18 7:02 pm
11/28/18 7:02 pm
Joined: Jul 2018
Posts: 103
London, UK
Ianbuck Offline OP

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Ianbuck  Offline OP

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Joined: Jul 2018
Posts: 103
London, UK
I'm in the process of fitting a new clutch to my 1970 A65 Lightning. Looking at the parts that came off and those shown in the parts catalogue and service manual (haynes), I appear to have a different sprocket, with the central bosses on both sides that are flush with outside casting of the driven teeth. I also have a spacer between the sprocket and the rotor.

When I search for the sprocket part number on line, I find a sprocket with a larger boss on one side.

Is my arrangement with the spacer a former owner's modification, to use a none original sprocket ?

Ian

Attached Files 20181128_181635_resized.jpg01-68-0205_03.jpg
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Re: Primary drive sprocket [Re: Ianbuck] #757453
11/28/18 7:58 pm
11/28/18 7:58 pm
Joined: Dec 2002
Posts: 3,275
arkansas
L
leon bee Offline
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leon bee  Offline
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L

Joined: Dec 2002
Posts: 3,275
arkansas
The front sprocket is for an ET setup, as on the Hornet. Has a little peg if nobody has knocked it off, to time the stator. If using a stator without the timing hole, as in regular ignition, you can just flip that disc around so peg points in. Or trade to somebody who wants it.

Re: Primary drive sprocket [Re: Ianbuck] #757454
11/28/18 8:00 pm
11/28/18 8:00 pm
Joined: Dec 2002
Posts: 3,275
arkansas
L
leon bee Offline
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leon bee  Offline
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L

Joined: Dec 2002
Posts: 3,275
arkansas
I just noticed you are in the UK, I suppose they may have used up some of those sprockets with just a spacer.

Re: Primary drive sprocket [Re: Ianbuck] #757466
11/28/18 10:13 pm
11/28/18 10:13 pm
Joined: Jul 2018
Posts: 103
London, UK
Ianbuck Offline OP

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Ianbuck  Offline OP

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Joined: Jul 2018
Posts: 103
London, UK
Thanks for the response. My sprocket is not in bad condition, although I was going to renew it to go with the new clutch and chain. The only sprockets I've seen have the longer boss, but now I know that is correct I'll buy one.

The spacer i have does not have a peg on it, or any evidence of one being there.

Thanks again

Ian

Re: Primary drive sprocket [Re: Ianbuck] #757493
11/29/18 3:40 am
11/29/18 3:40 am
Joined: Dec 2002
Posts: 3,275
arkansas
L
leon bee Offline
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leon bee  Offline
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Joined: Dec 2002
Posts: 3,275
arkansas
Could be something I don't know about. You can see the timing disc in the 67 parts book. Then you got the distance piece and maybe a shim on the other side.

https://www.draganfly.co.uk/index.php/bsa/bsa/a50-a-a65/1967/category/264-crankcase

Re: Primary drive sprocket [Re: Ianbuck] #757501
11/29/18 10:42 am
11/29/18 10:42 am
Joined: Jul 2018
Posts: 103
London, UK
Ianbuck Offline OP

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Ianbuck  Offline OP

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Joined: Jul 2018
Posts: 103
London, UK
This is what my engine looks like.

https://www.draganfly.co.uk/index.php/bsa/bsa/a50-a-a65/1970/category/340-70-crankcase

Although I appear to have a flat Hornet type primary sprocket plus a plain steel spacer between the sprocket and the alternator rotor.

Ian

Re: Primary drive sprocket [Re: Ianbuck] #757575
11/30/18 1:37 am
11/30/18 1:37 am
Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
I also have an ET-type (flat) crank sprocket with a spacer, but on my spacer you can see where the dowel was cut off.

I wouldn't be surprised if BSA in some cases used flat sprockets with plain spacers on non-ET models, e.g., to economize on parts.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Primary drive sprocket [Re: leon bee] #757606
11/30/18 12:33 pm
11/30/18 12:33 pm
Joined: May 2013
Posts: 5,125
Rotherham - S. Yorkshire
Allan Gill Offline

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Allan Gill  Offline

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Joined: May 2013
Posts: 5,125
Rotherham - S. Yorkshire
Originally Posted by leon bee
Could be something I don't know about. You can see the timing disc in the 67 parts book. Then you got the distance piece and maybe a shim on the other side.

https://www.draganfly.co.uk/index.php/bsa/bsa/a50-a-a65/1967/category/264-crankcase



So... Is the spacer machined with a spline or bolted to the sprocket? and does the rotor then not use the woodruf key on the crank? trying to work out what keeps it at that timing position?


beerchug
Re: Primary drive sprocket [Re: Ianbuck] #757653
11/30/18 6:45 pm
11/30/18 6:45 pm
Joined: Jul 2018
Posts: 103
London, UK
Ianbuck Offline OP

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Ianbuck  Offline OP

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Joined: Jul 2018
Posts: 103
London, UK
You can see in my photo it's a plain spacer and sits over the spines. The rotor uses a woodtuf key on the shaft.

Ian

Re: Primary drive sprocket [Re: Ianbuck] #757693
12/01/18 2:41 am
12/01/18 2:41 am
Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
To be perfectly honest, I never have figured out how that timing spacer is supposed to work. I didn't care, really, because I don't and never had ET ignition. I just have an ET-type crank sprocket and spacer (with the dowel cut or ground off). If I remember right, the alt. rotor that was with it had a hole in the back side to accept the dowel, although I'm not using that rotor any more. It also had a keyway for the woodruff key of course.

Ok, so the question is, what keeps the spacer in a particular position on the crank? Again, if I remember right, the spacer is not splined. And if the key locates the rotor on the crank, why is the doweled spacer necessary?

The only explanation I can come up with is that the dowel adds strength to the rotor mount. That is, I have seen wallowed-out keyways, although that only tends to happen when the rotor nut loosens. Not a serious problem for a non-ET ignition, but for ET, maybe?


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Primary drive sprocket [Re: Ianbuck] #757720
12/01/18 12:03 pm
12/01/18 12:03 pm
Joined: Jul 2018
Posts: 103
London, UK
Ianbuck Offline OP

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Ianbuck  Offline OP

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Posts: 103
London, UK
Just out of interest my rotor has 3 dowel holes on the back face with a letter S, M, or R against each one.

Attached Files 20181201_115637_resized.jpg
Re: Primary drive sprocket [Re: Ianbuck] #757722
12/01/18 1:05 pm
12/01/18 1:05 pm
Joined: Dec 2004
Posts: 9,662
Scotland
kommando Offline
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kommando  Offline
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Posts: 9,662
Scotland
ET was no longer fitted even to those bikes with an off road slant by 70 as the introduction of the 2mc capacitor in 69 gave batteryless ignition with normal points and condenser, So these ET parts you have were fitted later on, no doubt when spares were hard to come by or sitting on a bench close by and available.

Re: Primary drive sprocket [Re: Ianbuck] #757734
12/01/18 3:59 pm
12/01/18 3:59 pm
Joined: Jul 2018
Posts: 103
London, UK
Ianbuck Offline OP

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Ianbuck  Offline OP

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Joined: Jul 2018
Posts: 103
London, UK
It's very interesting to start uncovering the history of a bike. On face value my bike looks like an original 1970 machine, but it has an April 1970 engine in a December 1970 frame, and now I've found an earlier design of engine sprocket and rotor. The fork stanchions were triumph units with short tapered tops with lots of bits missing. Now fully restored to BSA spec.

I wonder what I'll find when I split the crank cases (next winter's project), hopefully after a summer of riding. 😎

Ian

Attached Files image003(1).jpg
Re: Primary drive sprocket [Re: kommando] #757811
12/02/18 9:41 am
12/02/18 9:41 am
Joined: May 2004
Posts: 3,892
Sydney Australia
B
BSA_WM20 Offline
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BSA_WM20  Offline
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B

Joined: May 2004
Posts: 3,892
Sydney Australia
Originally Posted by kommando
ET was no longer fitted even to those bikes with an off road slant by 70 as the introduction of the 2mc capacitor in 69 gave batteryless ignition with normal points and condenser, So these ET parts you have were fitted later on, no doubt when spares were hard to come by or sitting on a bench close by and available.


Remember it did not come off the production line yesterday so there is no reason to expect any part on the bike is original.
And BSA had a design rule that all new parts had to be backwards compatiable or be able to be made backwards compatiable with some "fitting".

All of the design egineers bitched about this in their memiors as it stopped the modernization of model till a new one came out.


Bike Beesa
Trevor

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