The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: Ted_Flash on 21.10. 2015 15:53

Title: Cush drive cam profiles - 1950 Plunger A10
Post by: Ted_Flash on 21.10. 2015 15:53
Hi All.

Just starting maintenance on annoying things that I've lived with for too long.  The bike snatches at low speed, so after renewing the carb I'm looking at the primary drive.  A new chain and a tensioner are on order.  The clutch looks relatively central (ie minimal bend in the mainshaft).

But I'm puzzled with the cush drive.  I've got a spare set and the cam profile of the sprocket side is different to the one fitted, in that it's lower (see pics)  5mm versus 7mm.  The set fitted has both the sprocket and sleeve cam peaks in contact for all its travel.  The spare has the peak of the sprocket cam out of contact until maximum rotation.  I know BSA redesigned the unit but not the details of what they did.  And maybe my spare is a mismatched pair.  Did the change keep only one peak in contact?

Title: Re: Cush drive cam profiles - 1950 Plunger A10
Post by: chaterlea25 on 25.10. 2015 17:50
Hi,
I'm not well up on the plunger models,
My opinion and experience tells me that the sprocket and sleeve profiles should match each other
HTH
John
Title: Re: Cush drive cam profiles - 1950 Plunger A10
Post by: morris on 25.10. 2015 19:58
Here's a shot of my plunger's cush drive and sleeve. This is a sleeve I replaced by a NOS but there was no significant difference in profile.
Sorry for the quality of the pictures. On the picture the sleeve's surface looks rougher than it is in reality.
It seems to me that there's something wrong with your spare set. The sprocket cam top should be much more pointy.
Title: Re: Cush drive cam profiles - 1950 Plunger A10
Post by: duTch on 25.10. 2015 20:21
 In addition to what Morris says, it could be a too-short spring... *????* (maybe S/A type which I reckon are shorter and fatter, as I said in Orabands thread).

  *edit 12/06/18 (June) adding link to ^above^ thread;
https://www.a7a10.net/forum/index.php?topic=9968.msg73326#msg73326 (https://www.a7a10.net/forum/index.php?topic=9968.msg73326#msg73326)
 
  Mine was doing something similar when the spring broke, and since replacing it (with I reckon a 'wrong' one), it just makes a bit of a clatter on kick-over