There have been some field reports concerning premature valve stem and guide wear in engines using separate rocker arms pivoted on a ball and stud with a nut. There is considerable evidence that unusual guide and stem wear have been experienced in these engines. Prior to the introduction of the separate pivoted rocker arm, however, there were many reports of excess valve guide and valve stem wear in engines with conventional rocker shaft and rocker arm assemblies.

Several reasons for the excess guide and valve stem wear for the stud type rocker arm have been advanced. There is much evidence that when misalignment is accompanied by poor lubrication, an unusual amount of pressure is exerted on one side of the valve guide by a forced action of the valve stem. This pressure is caused by the uneven force exerted against the tip end of the valve by the rocker arm. Naturally the resulting wear can occur regardless of whether the rocker arm is rotating from a shaft or is pivoted from a ball, but engines equipped with the ball and stud independent rocker arm are particularly dependent upon accuracy of alignment to bring about an even force of the rocker arm against the end of the valve stem.

It should be noted that reports have been received of original stud installations which were not exactly at right angles to the head, cylinder heads which were originally installed out-of-square or stud alignments which were not parallel to the line of the camshaft. Members have also found cylinder heads from original factory installations which had rocker arms with indents for the fulcrum ball sockets which were so uneven they produced an out-of-square position on the tips that contact the valves, thereby tilting the rocker arm and creating a problem at the push rod end.

Any misalignment on a stud equipped cylinder head will create an abnormal force on the end of the valve stem. Unless this condition is corrected, heavy erosion will be experienced on the stud and there will be wear on the end of the valve stem, the push rod end which contacts the rocker arm and the valve guide.

(P55)