Norman, you may be right about that Australian special but I´d first want to see a picture of it before believing it. Must have been very different from original. I am quite sure you cannot have that spring preload from original Vincent ESAs so as not to slam the end plate , the cam shape is just not fit for purpose - as Neville once observed with bang/left-bang/right stops when playing the throttle. What makes matters even worse with unhealthy preloads on the poor ESA resp. the sprocket face is all loads from springs plus extra thrust from torque of crank acting on the cam slopes goes onto the inner race of the outer main bearing, wearing both the sprocket and the race. Only minimal area there for taking all wear and load, the radius on the inner race reducing it even more. Looking at the Vincent ESA the angles of the gradients don´t get steeper than 35 degrees when lifted. The BMW cams approach 60 degrees and this fact makes the progressive action almost self locking approaching that steepness, not much depending on springs near block length and not adding much extra load onto the bearing inner race. Self locking on steep gradients is well known from worm drives: You can turn a typical worm drive from the worm but the drive self locks when trying to turn the worm by the crown wheel. That was the reason Sunbeam inline twins had to have two start extreme pitch worms in the rear drive. Otherwise you would not have been able to push the bike with engine stopped when the crown wheel drives the worm.
Anyway, all efforts to get the old ESA do its real purpose by adding high spring forces are just bad engineering by not understanding - or ignoring - basics of face cam shock absorbers. Old habits and thoughtlesnesses die hard when engineers just take over from old times , accepting too fast all to be good enough - that´ll do - without thinking.
Just came to an idea for those poor souls running the stock ESA : Target is to prevent the ESA from bashing the end plate hard, the springs will not do it alone -as everybody knows. You could do a test with taking out maybe two or more springs and replace them with a length of hard rod, nice fit in the spring bores. In the bottom of the bores sink a short legth of a thick O-ring, a bit smaller o.d. than bore, maybe 1/4 " long. Do a test in a vice and compress the lot so you can see what length of o-ring you need to almost press the ESA to its stops. This would offer a softer sort-of- progressive stop and no more hard slam. Rubber gets steel hard when in a closed volume so some experiment with length and diameter of the rubber can help for feel. Don´t see any risk in trying on the bike, the rubber is in the bottom of the bore - unlike the broken coils of springs flying around in the primary.
Vic
Sunbeam worm drive:
BMW type ESA :
Vincent ESA :