comnoz said:
I have noticed that the greatest wear in the Norton cam and lifter occurred at a point just after maximum lift when the valve and lifter comes back into contact with the cam after being "launched " from the peak of the lobe. Jim
The impression that it is normal for a valve-train to have clearance between it's parts under normal operating conditions except when a solid lifter is resting on the base circle of the cam lobe would be wrong. When parts lose contact with each other while the lifter is on a ramp or lobe then you have valve float and are on your way to making junk.
Only a poorly designed cam, valve-train or valve float would let a valve-train be "launched" and have to land with enough force to damage itself, and I can believe that the Norton valvetrain with all it's disadvatages and faults will be the one to have problems if they are possible.
The Norton valve train has almost every disadvantage one could think of for an overhead-valve valve-train. The worst part of it is it's low rocker-arm ratio which is almost down to 1:1. This means that the entire valve action that is needed, acceleration and lift, has to be ground into the cam lobe itself, and that limits valve action a lot compared to an engine like a General Motors pushrod V-8 which has historically used rocker arm ratios between 1.5-2:1.
If someone moved the pushrod ball on a Norton rocker arm in towards the pivot to get the rocker ratio up to 1.3:1, which is a possible modification to the stock parts, the a cam could be ground on a larger base circle that is much stiffer than a stock cam. the cam could even be ground full-relief on a blank that is almost the size of the standard cam tunnel. This is because the higher rocker ratio would let the valve have adequate lift that would not all have to be ground into the lobe. The lobe could be far less radical than they have to be now, with much less and gentler movement of the lifter and pushrod than currently is used.
Also because the leverage advantage a high ratio would give to the valve spring in controlling the lifter-side of the valve-train, the same or even a weaker valve spring could be used for a given rpm.
The Norton engine is a real POS design for high-rpm work, but still a lot make it their hobby to try and get it to do the job of a short-stroke-OHC, multi-main-bearing engine.
A high rocker ratio would let the valve move faster and spend more time at a useful lift for any given duration, enhancing the only thing the Norton twin gets close to having as a strength, which would be making useful power at rpms below that which cause it to fall apart.
Instead of concentrating development on High Rpm power from an engine that can not stand it, and turning the engine into something completely different to what ever came out of any factory in the U.K., a high rocker arm ratio used to produce high lift with a moderate duration could squeeze mid-range torque out of a Norton that no one ever has before, and at an rpm level that would let it be done without completely re-manufacturing it into something alien.
Development in this area might let an engine with a re-worked standard head running high-ratio rockers, run in the mid-range like a Full-auto head with standard rockers and cam profiles....at much less cost.
Getting back to Heinz Kegler's idea of having the rocker arm contact the center of the valve while it is heavily loaded during the acceleration of the lifter up to the nose of the cam, the Nascar tuner Smokey Yunick agrees about that being the point of highest stress during operation.
Also there are two different kinds of loads possible in a poor valve-train like the Norton's. If you have a glass table you can gently set an Anvil onto it and it will hold it's weight with no problems, but you can drop a penny on the table from the height of a few feet and possible chip, crack or even shatter it. In a well designed valve train made entirely from glass, or maybe hardened steel, there are ideally no shock loads during operation, the springs keep everything together during the lift cycle and the cam profile accelerates everything while keeping below the limits of launches and drops.
What Kegler was concerned with was dealing with the maximum normal pressures and side-loads endured by the valve-train and valve guide during engine operation, which is something that is going to occur at any rpm from idle-speed on upwards. The sort of shock-loads induced by poorly designed lobe profiles, weak valve springs and high rpms were probably not what he was aiming his solutions and theories at.....
