Hi John,
Your set up sounds quite different to mine, the only hubs I've seen without the lip is the A50/A65 version. That too runs a thrust washer as you have described. Sorry to hear you still had slippage after fitting a new clutch.
Here's a ref to the assembly photo on SRM site which shows the last closing plate being plain steel under the ally pressure plate. This clutch has 5 friction plates and 6 plain steel. If there is a plain steel at the top of the stack then there must be one at the bottom (against the lip).
http://www.shop.srmclassicbikes.com/product/triumph-pre-unit-4-spring-clutch-solid-centre-drumThe SRM hub for A7/A10 SA models with 4 spring clutches is this one
http://www.shop.srmclassicbikes.com/product/centre-drum-4-spring-type-a7-a10-swingarmand it looks exactly the same as my Feked solid hub (made in England!) with a lip at the rear. I bought the standard plate stack from SRM (5 friction plates and 6 plain steel plates).
RogerSB put up a very good write up on his assy with a schematic showing where all the bits go. You can find that at reply #98 in this thread. The thrust washer is there but it goes to the rear of the basket between it and the adapter flange. You can see from his photo how much bigger the flange dia is to take the thrust washer. I guess it just takes up a lot of that excess clearance that allows the basket to wobble even when the hub is snugged up tight and the center nut is fully tightened.
So you would have 7 friction plates and 7 plain ones I gather if the first one is a friction plate at the rear against the basket. That would give you a lot more grip and I guess more grab but the spring load is spread over more area so maybe not.... I remember checking to see if I could possibly load another pair of plates into my set up but that would not have worked! The point about oiling the plates is interesting. Maybe a bit of oil would improve the feel and perhaps this does occur over time as there is hot oil mist around the plates the whole time she's running. My new plates were bone dry, grey and furry/fibrous to the touch.i.e. very grippy. The old ones were black shiny and appeared to have absorbed oil over time yet they were not wet with oil. They felt a lot more slippery to the touch.
