The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: zitman on 21.04. 2010 22:17

Title: Primary drive Engine sprocket
Post by: zitman 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
Title: Re: Primary drive Engine sprocket
Post by: LJ. 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.

(http://img.photobucket.com/albums/v631/mr-lj35/DSCF3739.jpg)

(http://img.photobucket.com/albums/v631/mr-lj35/DSCF3747.jpg)

Photos via Photobucket...
Title: Re: Primary drive Engine sprocket
Post by: wilko on 22.04. 2010 10:39
Thank the lord for pre-unit. Imagine if that happened to unit cases!!
Title: Re: Primary drive Engine sprocket
Post by: muskrat on 22.04. 2010 13:06
Ouch, looks like the cush nut had come off once as well.
cheers
Title: Re: Primary drive Engine sprocket
Post by: zitman 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
Title: Re: Primary drive Engine sprocket
Post by: BSA_54A10 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 ?
Title: Re: Primary drive Engine sprocket
Post by: MikeN on 26.04. 2010 12:11
Thank the lord for pre-unit. Imagine if that happened to unit cases!!
I never new he designed it???
Title: Re: Primary drive Engine sprocket
Post by: muskrat on 26.04. 2010 20:09
On the 8th day he created A7/10's.  *smile*
Title: Re: Primary drive Engine sprocket
Post by: Brian 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*