Valve rotation can be accomplished if the rocker only hits the edge of the valve. The rocker tip will try and pull the valve stem with it, thus turning it.
Think of a lawn mower self propel unit that uses two wheels, the smaller drive wheel with a horizontal axle runs on a larger driven wheel with vertical axle. By moving the small wheel closer or farther from center, the larger wheel spins faster or slower. Now change the smaller wheel to rocker tip, in its full range of motion, it follows a arc, which is just a small piece of a circle, so unless the rocker is right over the center , it going to rotate the stem.
Its true can can alter the start stop points of the arc, but the differences would be hardly measurable. The side to side (level) far out weighs the starting/ending points. The rocker ratio is set by location of the pushrod and the pushrod length only changes the length of the arc. A proper designed and ground rocker, will only use a small portion of the valve stem with a low lift camshaft, not even half the stem width. If you find a valve stem with a wear line across the face, you can bet the rocker is worn since the valve quit rotating.
Joe
Last edited by Joe H; 01/20/2012 4:41 PM.
