BSA Owners' Club Workshop Discussions

The BSA Workshop => Singles => Topic started by: pete lafeet on 24 Aug, 2020, 17:46

Title: B31 1958 Clutch arrangement
Post by: pete lafeet on 24 Aug, 2020, 17:46
I hope someone can help with this please. I am having clutch slip which I have tried unsuccessfully to adjust away. So I stripped the clutch and found there is only 4 friction plates, I believe 5 plate is the correct number. There are 5 plain plates which I think is correct. Can i just add a friction plate to the end of the stack? Do I start with a plain plate and if so is it correct to end up with a friction plate next to the pressure plate.
Title: Re: B31 1958 Clutch arrangement
Post by: idie on 24 Aug, 2020, 18:34
That is the right amount for a B31. If you want a 5 friction plate clutch you will need a deeper clutch drum. One off a B33 or an A10.
Title: Re: B31 1958 Clutch arrangement
Post by: JulianS on 24 Aug, 2020, 18:43
Cross section of the alternator B31 clutch.
Title: Re: B31 1958 Clutch arrangement
Post by: idie on 24 Aug, 2020, 19:07
Ah you didn't say it was an alternator clutch which is a Triumph one.  Are you assembling it correctly. It may look as if the drum is acting as a plain plate. You start with a plain plate then friction plate and so on. If still having a problem you will need a deeper drum from a larger capacity bike to get the extra plates. Make sure it is one with the built in rubbers.
Title: Re: B31 1958 Clutch arrangement
Post by: pete lafeet on 25 Aug, 2020, 11:15
Thanks everyone. The bike has an alternator and looks like the clutch has the cush drive in it. Whats puzzling me is that the spring nuts are way down the screws, nowhere near flush or just under. Ill try to put it back together and post a photo to show what I mean. Sorry to labour the point, I'm new to classic bikes, but everything I have found, Haynes Draganfly etc states 5 friction plates for my year of B31.
Title: Re: B31 1958 Clutch arrangement
Post by: JulianS on 25 Aug, 2020, 11:51
Is there sufficient space in the chainwheel and on the drum to take another plate? If yes you could try it but you need to be sure it will be retained within the drum and not slip out of place when the clutch is withdrawn.

The alternator A10  models of the time used a similar 4 spring clutch but with a deeper chainwheel and centre to take its 5 bonded and 6 plain plates. The same bonded and plain plates were used for both models.
Title: Re: B31 1958 Clutch arrangement
Post by: pete lafeet on 25 Aug, 2020, 17:35
Thanks JulianS you are most helpful. I don't know for sure if there is enough space for another plate. I don't have enough experience with this type of thing yet. The extra plate would be a bonded plate I assume, which would end up next to the spring plate. Would that be ok? Also I have totally confused myself looking at the parts list for this clutch on Draganfly. There seems to be two spring cups and different springs although my springs look like the 5 plate clutch springs but the spring cups look like the 4 plate type?
Title: Re: B31 1958 Clutch arrangement
Post by: JulianS on 25 Aug, 2020, 18:52
I would not put a bonded plate next to the pressure plate - tha later is not designed to work with a bonded plate - the contact area is too small and I suspect that it would soon cut into the bonded surface on the bonded plate and give you other problems.

The other issue to be very sure of when considering adding a plate is whether, when the clutch is disengaged, that plate can move clear of the chainwheel and/or centre drum and drop.

The spring cups, I think, are about 1 inch long and the A10 type are 1 3/8 inch long.
Title: Re: B31 1958 Clutch arrangement
Post by: Stebbing on 26 Aug, 2020, 12:56
I've just taken my B31 (alternator model) clutch to bits. It has 4 friction plates and 6 metal plates. The previous owner attempted to repair it then just packed them all back in any order. I assume it has a metal plate at the front and back then the four friction plates sandwiched between. Any advice?
Title: Re: B31 1958 Clutch arrangement
Post by: Stebbing on 26 Aug, 2020, 12:58
See my post above.
What do I do with the sixth plate?
Also, where did you get the diagram showing a cross section? Very useful.
Title: Re: B31 1958 Clutch arrangement
Post by: JulianS on 26 Aug, 2020, 13:26
The cross section came from the owners manual.
Title: Re: B31 1958 Clutch arrangement
Post by: idie on 26 Aug, 2020, 14:26
As I said before start at the back with a steel plate then a friction plate. You should finish with a steel plate.