This is my experience with the servo clutch in the photograph:
Between 15-20 years ago Heinz Kegler was telling me how he had let one of the three servo clutches he had acquired when he worked for Norton go with a 650ss bike he had sold. He gave me the guys contact information and when I talked to the guy he said he was not really interested in the clutch, it was supplied with his bike extra in a box of bits. So I bought the whole box of parts from him clutch included.
I was riding a 1961 650 Norton on a daily basis and the clutch was a hard pull at the lever if I had the screws tight enough to stop any slip under hard use, the clutch lever pivot was beginning to wear oval! Also even though I was right-handed I could peg one of those machines you see at amusement parks that test your grips with my left hand.
So I popped the Servo Clutch in the bike and tightened the screws up so the pressure plate stayed flat when the lever was pulled, and so that the lever pressure was very light and comfortable to pull, it was just a guess. Well it worked great from the start. My lever pivot stopped wearing, the clutch never slipped under power, just when it was supposed to on fast downshifts into a low gear or when chopping the throttle in gear while coasting down steep hills.
I used the original clutch plates from 1961 with the servo clutch for over ten years and never had one problem with them, I ever took the bike to a drag strip for multiple runs one weekend.
So now I am spoiled. Once you run an AMC clutch with a servo center like this you will never want to go back to the old one ever. It makes the lever pull like that on a modern bike and you simply quit thinking about it. I wish I had one of them for each of my old Dominators and each of my father's old Matchless bikes. With the light spring pressure you can forget about stretching or breaking clutch cables and wearing out all the parts between the lever and the pressure plate.
If someone is making and stocking batches of AMC clutch centers currently and the splines on them are being CNC machined, then it just does not seem like it would be that much effort to alter the CNC programming to cut the splines with the specific spiral needed to convert it to servo action.
So in the end, there are many benefits to this clutch and zero drawbacks. All that has to be done to use stock clutch plates is to machine the splines a bit narrower to make up for the angle, which is a detail that a good CAD program should do easily. And yes they would be hardened material if they were going to last a long time.
Besides the loose servo clutch in the photo, there is also one in Heinz Kegler's old Daytona 88 race bike, which was used in the bike throughout the sixties and early 1970's for road racing, it also works like a charm with very light lever pressure and the bike shifts like a dream, and despite it having well over 50 horsepower and a hard hit when it comes on the pipe it does not slip a bit.
If someone has a basically stock Norton or Matchless road bike that they enjoy riding very often, then one of these servo clutch centers will double the enjoyment they get out of it, especially in stop and go traffic, by cutting the lever pressure by what feels to me in half.
