The surface fatigue on the cam lobe nose is a result of spring pressure - it can't be anything else. The problem is there is over 5 different manufacture types of springs being fitted, of which two have been tested. There is nothing anywhere to suggest that any real testing of actual spring rates, configuration, fitted heights, lobe nose pressures etc that enables anyone to say that 'this configuration will enable the cam to last x thousand miles' very few Norton owners record this data.
The feedback so far is that the for those that want high spring rates for performance cams then standard springs will easily fill this role but you need to check for coil binding. But many in the cam design and manufacture world are saying these pressures are way over the top, but can't suggest any figures that would be suitable.
This is further compounded by the fact that many may have felt what they believe to be valve lofting (bounce) at high rpm, has anyone actually physically seen this and recorded it with a camera. I suggest it could also be resonance which would give the same affect but is different in how it occurs.
Fitted height is important as it determines max lift pressure, so to keep the max pressure down you may need to go to a weaker spring rate, determine the max pressure you are aiming for, work out your valve lift, use the spring rate and work back to find your fitted height and at the same time making sure you do not get coil bound. We believe that those who have made changes to avoid coil binding have actually lowered their max pressures to a lower level.
I have just fitted and currently running a new cam, it has 11.24mm of valve lift and uses radiused followers with the cam ground to suit, predictions on paper using a standard head, with 1mm modified valve stems is that fitted pressure would have been 89 lbs, max 246 lbs, when fitted with the FA head I had fitted 59 lbs, a surprise, and max pressure 199 lbs as my fitted heights were different to a standard head, It is running nicely and will hopefully be dyno'd on the 31st. It will also be ridden to Austria if it survives the dyno.
The standard springs have not changed since 1961 when they were changed to to suit a performance cam at the time which went on to become the 06.1084. in that day and age, the idea was 'that should be about right' and a 'add a little more to be sure' were most probably the norm. Currently with a standard cam and springs you are looking at around 104 lbs fitted and 226 lbs max. If you only changed the cam to a higher lift version ie PW3 and did not change anything else you are now at 246 lbs max lift. This for an engine that max revs at 8K is considered way to much pressure these days, with some suggesting that this is where they would want to be with stock racer at 10,000rpm and above.
Some have also found that too much and lift and the thought process that more spring pressure to control the vale gear have found it costs rpm and saps power, some automotive cams have been modified to lower the lift and re-tested and the engine has been found to rev higher and not have a reduction in power, the customers requirements were still exceeded by using less lift.
Sadly we have established some knowledge, but still don't have any concrete answers or solutions.
Tappets - some like them to just drop in, OK with a new barrel, but what if they drop in a used barrel - how much clearance do you have? Some can wield a spanner and that's it, they do not know or can't be bothered to fit a crucial part like a tappet. Yes, it is time consuming, but not hard and it is worthwhile.
Being cast iron they are a pig to grind and the stress in the material will take charge when released from the mandrel and thus the little high spots. Of all the people in the Norton world, and many who worked for Norton in Wolverhampton and Andover in the past cannot remember how they were made then to avoid the high spots.
See you at the open day on the 28th at Andover Norton, come down and we can discuss further.