BSA motorcycles of this vintage had either three or four clutch plates which had cork inserts, which were sandwiched between plain steel plates. The plain plates were fixed to the clutch hub with lugs in the centre, while the cork plates were fixed to the chainwheel by lugs on the outside.
Under spring compression all plates moved in unison. When they were separated by squeezing the clutch lever, it allowed the two sets of plates to move independently, so the engine could drive the chainwheel but the gearbox would not drive the rear wheel while the clutch lever was held.
After removal from the clutch, the friction plates look like this ...
The 24 friction inserts can be pushed out of the steel frame, and the frame then cleaned up.
A trip to your friendly local winery can often prove fruitful when searching for suitable corks to make the new friction inserts from. In my case I went to Hardy's Reynella Winery, and the friendly lady in the tasting room was only too happy to listen to my problem, and she sent me away with a bag of wine corks. The most useful proved to be from champagne type bottles - there are no corkscrew holes or damage. I boiled up the corks, and after about twenty minutes they resumed their original cylindrical shape.
I made a metal template for the new inserts, making sure that it was slightly larger than the holes into which the new cork inserts had to fit. Each insert needs to be about 1 mm oversize in all directions, and they must be about 4 mm thick, to allow for sanding after insertion into the plate. This makes sure that the cork surfaces are aligned to bear evenly on the steel plates when the clutch is finally reassembled.
After cutting and inserting the first cork, I realised that there were only twenty three to go to complete the first clutch plate, and another forty eight corks to complete the other two friction plates. But, being an optimist, there is always a positive way of looking at it - if I had a B33 or an A series twin, I would have had four friction plates instead of three.
After all the corks had been inserted, they had to be sanded. I glued a piece of sandpaper to a flat board, and carefully sanded each side of each completed plate until the corks were all level and the right thickness.
The final product as seen above may not look very pretty, but I thought that once these plates were sandwiched between the steel plates, with the cover plate replaced, and the primary chain case was bolted into position, you and I will be the only ones who know. As long as they work as well as the originals, who cares.
I would like to thank John Simpson of the BSA Owners' Club of S. A. for the help and information he provided on re-corking clutch plates.