Hi Newsh & Thor, Good idea how to work out formula. This works with even very, very worn plates.
7 plate friction pads look worn out when new compared to 6 plate. So long as you have visable friction material with zero glue showing through, any where on the friction pad surface, they will still grip. How long will it be before worn to the glue is a different story. If clutch is set up perfectly like it should be with no slipping the very thin friction pads will last a long time. Many thousands of miles. 15K+. Even minor slipping under load will very rapidly wear the friction pad to the glue.
Obviously if the friction pad is worn off it will slip. I know some clutches are all metal to metal, but these can't do that.
We'll back up. There is a little hitch in the way the first pad might fit into basket... The friction pads even new are very thin. Original Triumph basket has a fairly sharp square corner at bottom of basket. This allows the thin pads to nest properly into the back of basket. All the reproduction baskets I've seen have a rounded radius at back corner of basket. So the metal of the friction plate fouls the radius & first pad doesn't lay flat. Now first pad is in a little crooked. All the rest of the discs end up a little crooked. The tend to slip & drag as you might think. The cure is to chamfer the outside edge of first friction plate such the plate lays perfectly flat with a little wiggle room. Of course the thicker friction pads of a 6 plate kit hole the steel of plate above the radius.
On a used clutch as you have, I go through the bunch & find the most worn friction pads. I place that plate in first, worn side to basket. However, you must be extra diligent to chamfer it as it's even more likely to foul the radius. This is very important stuff. I'll show so photos.
Now that's out of the way. Take all 14 of you plates after cleaning & stack them all up in order you'll assemble them. Squeeze them tightly with one hand & measure thickness of the stack with vernier calipers & record. Do this around the stack in 3-4 places & average the thickness. This called stack height. Nominal stack height is average of 1.400".
A new Triumph cork 6 plate kit of all 12 plates will be about 1.400 thick. That's where that nominal comes from.
Then factory tightened spring nuts flush with end of stud. Now we have 2 know values.
I expect you Hyde pack has taken some wear. We could figure this out if I knew your actual stack height. But for this exercise, we'll call the stack height 1.310". I've seen this in real life. So.... Were .090" thinner than nominal. Write that down....
We'll oil & install all the plates. Tighten the nuts down until dome is flush with ends of studs. ( you don't have domed nuts but bear with me).
So just to get the factory spring tension we need to go .090" deeper with nuts. Make sense?
We can set depth gauge of calipers to .090 & measure it or set by rotation of nut.
The stud is 1/4-26tpi CEI (the manual still uses CEI). We divide 1.000" by 26 = .038 rounded. One inwards turn of nut goes .038 deeper. .090 divided by .038 = 2.4 turns (rounded off). That's going to be a little less than 2-1/2 turns.
So we do that. Only do we have factory spring tension on a 650 spring. Over time I've found that's often not quite enough for long term durability. Another 1-1/2 turns will be very beneficial, yet only increase lever effort slightly.
If I was installing new friction plates I would go an additional turn to compensate for the rapid wear as the fuzz wears off & new plates settle in.
I've found if you use springs that are indeed to original 650 specs with length, number of coils, wire diameter, this formula just works. And works well. The formula also works to compensate for wear on 650 plates.
Spring binding... Since we are starting with pressure plate deeper in the basket by .090, we can go .090 without even exceeding the effective nut depth. You can go several turns deeper with 650 springs before they spring bind. If you want to go deeper while pulling clutch lever, at the same time watch pressure plate stop lifting as you feel clutch lever suddenly not want to move farther yet lever is not to grip. That's when springs are bound.
Also... Thust washer.... As thrust washer wears, it gets thinner. The basket moves to right in comparison with the cush hub. The cush hub holds the studs. So now you have effectively lost spring tension. Comparing different makers of new thrust washers, they vary a good .010". Some new are sold that are thinner than removed. Keep this in mind. Do you need to go a little deeper with nut to compensate for thinness of thrust washer. I'll only use Kibblewhite C630 thrust washers anymore as they are so durable. There are a few makers of solid "bronze" thrust washers. They are not all created equally!! I've been disappointed with all but the Kibblewhite. Unless you know seller is selling genuine KW, you must buy directly from KW. Don't be fooled, put the beveled side towards basket or it will fall off shoulder.
Thor, unless Todd can tell you exactly what part of his Allen nuts are where Triumph's dome is, you'll be doing trial & error setting nut depth. If you invest in original version nuts you'll be following a formula that does work well. How much does the original nuts cost. Is the cost worth knowing what works or not. You'll decide that. Those nuts were made for somebody that had a piece of crap nut tool that skipped, & damaged head of nuts. Or user had good tool & let it slip...
I can tell you, you follow this formula with the proper motor oil, which you say you now are using the clutch won't slip. If it does you have very bad wear inside the cush hub & it's pulling the plates crooked, separating them under heavy load. The spider wears much more than back plate. New cush hub generally has about .012-.017" end play fitted to basket. When end play gets to about .030" you may be seeing problems. When end play gets to .040+ it will do odd things like slip at times & not others. It can also start to drag.
The photo shows how deep this nut needs to be. This was will all new Aerco friction & steel plates. I expect you'll be deeper. This photo was with first fitting to test the steel plate with Aerco. After a 100 miles I installed the large diameter Britech alloy plate. The MAP plate replicates the operation the Britech gives. Britech is no longer made.
Also with new plates, trial fit sliding on grooves, they may (will??) need a little filing to slide freely.