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Author Topic: Primary drive Engine sprocket  (Read 1995 times)

Offline zitman

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Primary drive Engine sprocket
« on: 21.04. 2010 22:17 »
Hi all,

1959 A7SS.

I had my primary chain snap a few weeks ago, luckily just as I was moving off so no damage to anything else!

When I replaced the chain I upped the sprocket on the end of the crank to a 21 tooth from the standard 18 tooth.  The bike pulls it fine and revs much lower now.  I was just wondering if anyone else had done this?

Z
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Offline LJ.

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Re: Primary drive Engine sprocket
« Reply #1 on: 21.04. 2010 23:27 »
Not very nice when a primary chain snaps! Mine went while travelling at 40 mph, happens so quick, huge bang then high revs, clutch in and brake to a halt.





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Ride Safely Lads! LJ.
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1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
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1961 BSA A10  650cc Golden Flash-Red

Offline wilko

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Re: Primary drive Engine sprocket
« Reply #2 on: 22.04. 2010 10:39 »
Thank the lord for pre-unit. Imagine if that happened to unit cases!!
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Online muskrat

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Re: Primary drive Engine sprocket
« Reply #3 on: 22.04. 2010 13:06 »
Ouch, looks like the cush nut had come off once as well.
cheers
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'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline zitman

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Re: Primary drive Engine sprocket
« Reply #4 on: 22.04. 2010 22:39 »
Looking at that I was lucky my went just as I was moving off.  Still embarassing though as it was the third weekend on the trot  I had failed to get where I was going!

Z
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Offline BSA_54A10

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Re: Primary drive Engine sprocket
« Reply #5 on: 26.04. 2010 10:17 »
As Musky noted, it looks like the cush drive nut has come loose.
This will allow the sprocket to move and can cause the chain to collapse due to too much side force on the side plates.
Did you fit a new lock washer under the cush drive nut ?
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Offline MikeN

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Re: Primary drive Engine sprocket
« Reply #6 on: 26.04. 2010 12:11 »
Quote from: wilko on 22.04. 2010 10:39
Thank the lord for pre-unit. Imagine if that happened to unit cases!!
I never new he designed it???
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Online muskrat

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Re: Primary drive Engine sprocket
« Reply #7 on: 26.04. 2010 20:09 »
On the 8th day he created A7/10's.  *smile*
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'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
Australia
Muskys Plunger A7

Online Brian

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Re: Primary drive Engine sprocket
« Reply #8 on: 27.04. 2010 09:50 »
I reckon he created the A's on the first day Muskrat, then he went on to make all that other mundane unnecessary stuff. *smile* *smile* *smile*
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