Number of clutch-plates, what's the truth ?

[Nitti]

The annual Rockers vs Mods run in Stockholm last weekend really strained my clutch, traffic-lights+sidecar+passenger+an overweight pilot, really stressed the Golden Flash clutch to its limits, with severe slippage as a result.
When I ripped the clutch apart I found something that I have not seen on any bike before, the oddity was that there are two steel-plates next to each other, in the bottom of the clutch-cage that is.
When looking in alla available manuals, spareparts-list I can not see this described anywhere.
BUT, the spareparts-list mentions that my bike, a 1953 plunger Glden Flash, should have 5 friction- plates and 5 ordinary steel-plates+the thisker steelplate.

When summing this up, it actually menas that there will be two steel-plates next to each other, strange.
My reasoning ;

Pressure Plate = PP
Friction Plate = FPS
Steel Plate = SP
Thicker Steel Plate = TSP

PP+FP1+SP1+FP2+SP2+FP3+SP3+FP4+SP4+FP5+SP5+TSP

QED

Am I right, if so why are there 2 steel-plates ?

Regards
Nitti

[bsa-bill]

I think I would go for this

PP+SP1+FP1+SP2+FP2+SP3+FP3+SP4+FP4+SP5+FP5+TSP

all the best - Bill

[Nitti]

Hey,

Thanks for the alternative, but...
I'm curious to understand your reasoning why this would be better, my guess is that in theory would the SP1 being next to the PP even out the pressure, was that your thought, or ?

Still though, the question why there are 2 steel surfaces next to each other still remains to answered.

Regards

Nitti

[LJ.]

Is this the six or four spring clutch?

[Brian]

Nitti, the parts book is wrong. You should not have two steel plates together. Start with the thick steel one on the inside and work outwards alternating between steel and friction. The only thing I can think is that at some stage in the bikes life the friction plates have worn down and someone has put the extra steel one in to take up some room. These plunger clutches are a very good clutch and should work very well once you have everything right.
Put new friction plates in and a new set of springs, make sure there is no wear on the fingers of the basket and you will get many miles of reliable service from your clutch.

[tombeau]

I never knew about the thick plate!
Iain

[dpaddock]

Bill has the correct sequence; use the thicker plate against the bottom of the stack.
BTW, there's no 4-spring alternative for the plunger clutch that I know of.
And the BSA Spares manual is correct as published.

[Brian]

I will stick with my opinion that the parts book has the no. of plain steel plates wrong.

I have three plunger A models and have at various times had them all apart, mine all have 4 plain steel plates and all work well.

In D.W. Munro's book of BSA twins on page 84 there is a picture of a dismantled plunger type clutch which clearly shows One thick steel plate, 4 plain steel, 5 friction plates and the pressure plate. D.W.Munro was BSA's technical manager so I think he knew what he was on about.

[Nitti]

Thanks for your insights, I also tend to believe that the spare parts list, despite being the original one for "A" Twins 1949 to 1953, is wrong.
It clearly states that there should be 5 pcs Driven Plates (67-3241) + 5 pcs Driving Plates (67-3242) +  1pce Driven Plate "Rear" being the thick one (67-3240) + 1 pce Spring Plate (67-3245).

If following this there will always be 1 Steel Plate rubbing either the Spring Plate or the thicker Steel plate, which is illogical, as we all seems to agree upon.

Regrads
Nitti

[dpaddock]

Well, Nitti, we don't ALL agree; it's not illogical for the spring plate to rub on the first plain plate. Think about it.

[bsa-bill]

If you think about it the spring plate needs to press against a flat surface that will then transfer pressure to a friction plate in a universal even way ( we hope)
The spring plate pressing against a friction plate ( I have to admit to not being familiar with your  model ) may not transfer pressure in the same even way.

All the best - Bill

[trevinoz]

Brian is correct. When I stripped my Star Twin I found the thick plate at the bottom of the stack with friction plates alternating with thin plates and the pressure plate bearing on the top friction plate.
The four spring clutch [triumph type] has the pressure plate bearing on a steel plate.
   Trev.