INTRODUCTION

BACKGROUND

What is MID-LIFT?

TERMS & DEFINITIONS

Using the outline of the original Chevrolet "shoe" tip rocker arm, Harland Sharp set the bottom diameter of a .625" roller to trace along the shoe's contact surface. This had the effect of shifting its "axis" of its critical point of measurement up more than .300". This had the effect of raising the TAIL (or pushrod cup)  too high, as its position was not adjusted for in this error, which was half of the diameter of this roller. That .312" equaled more than a 13 degrees of error, on a radial instrument that would only rotate about 25 degrees for a .600" Valve Lift!

This problem lasted for more than 20 years, and continues to this day, even though most top manufacturers are well aware of the Miller Patent and the consequences for keeping this error on their original designs. These consequences are: (1) additional (and unnecessary) extra crank rotation at all points of valve life to open the valve; (2) excessive side loads to the valve and guide with increased and rapid wear; (3) increased rotational drag on the entire engine by 15 to 40 pounds (or more) of extra torque; (4) increased acceleration of valve spring harmonics, killing springs prematurely and requiring excessive spring pressure to control, thus taking away more horsepower from increased rotational drag; and (5) excessive wear (and drag) on lifter bores from pushrod side loads, as well as wear to pushrod ends.

In more severe "bad geometry" cases, you will see the pushrod literally want to push the side of the cup out of position at full valve lift because it has arced up and "in" toward the adjusting screw (or shaft centerline) from this too high an angle. This is the fundamental mistake that echoes throughout every top rocker arm manufacturer in existence today. Some less than others; all because of this simple mistake in 1958, and the arrogance to keep selling the error.