BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: MALCOLM.JOHNSON on 28 May, 2017, 21:44:22

Title: Plunger A7 clutch
Post by: MALCOLM.JOHNSON on 28 May, 2017, 21:44:22
On rebuilding my 1952 A7 clutch, I notice that if I put a straight edge across the friction surface of the outer pressure plate (67-3245), there is a pronounced "dish" ie it is not flat. The "dishing" is uniform across all diameters.  The difference is about 1mm at the inner diameter of the friction surface. I would not expect this, but on looking at a spare clutch that I have, it is exactly the same? Both correct or both wrong? All other plates are dead flat. Don`t want to buy new if that is how they are.

The outer plate is made up of a pressed spring plate, spot welded to what looks like a standard plain driven plate. Does the spot welding create this "dishing"? How/why would it need to be dished. Could easily be overlooked.

Whilst on the subject I am contemplating using "Surflex type friction plates, which in many applications are wet with oil, but not so in this type of BSA clutch if properly sealed. Do we still use the cover?   Appreciate informed thoughts on this.  Thanks.
Title: Re: Plunger A7 clutch
Post by: 6372N23-11 on 29 May, 2017, 12:46:20
Malcolm .If your clutch anything like my B33 clutch I would ditch it and get a decent one .My 58 A10 has a Triumph 4 spring fitted ,both bikes have SRM clutch pressure plates fitted ...I think that the 'dishing' will not matter much if you intend to persevere with what you have .by this time all sorts of things can complement a clutch from not working as it should ... Good luck .Rich.
Title: Re: Plunger A7 clutch
Post by: MALCOLM.JOHNSON on 29 May, 2017, 22:05:52
Hi, Thank you for the advice, but I too have an A10 special with a 4-spring clutch which is good, but equally I currently have a B31 and have owned both another A10 and B33 that had the 6 spring clutch fitted. The later 6 spring clutch when set up correctly and fitted with parts that are not worn out or damaged, can be a perfectly good clutch too. It is my intention to do the same with my plunger A7, which to me looks a better design than the later clutch fitted to the S/A models which is the one I feel you are referring to, but I accept that experience may change my view on that.  I am also not sure that the 4 spring clutch can be made to fit the plunger models anyway.

This is why I need to find out whether the dished plate is a design feature or not, for interest if nothing else. If it is not correct I will buy new.

I also would also like views on the experience of others, what Surflex plates are like in a "dry" environment, as such inside the sealed clutch of plunger models.
Title: Re: Plunger A7 clutch
Post by: MALCOLM.JOHNSON on 19 June, 2017, 11:50:15
Since my last post, I have come across several used pressure plates and all barring one were dead flat, which is what we would expect. The odd one was dished exactly like my original two. I bought one of the flat ones and is now installed.

I drilled the six spotwelds through on one of the old ones to separate the two pieces and it is easy to see that the dishing of the flat plate occurred during the spot welding process during manufacture as the outer piece is not a dead flat surface, probably due to not being pressed to shape enough. The dished ones have probably given thousands of miles of service, once bedded to the outer friction plate.

One of the dished ones is not wasted - cut out the centre to allow for a socket and welded a bar to it, to lock the clutch centre when tightening the nut.