History Of MID-LIFT

INTRODUCTION

BACKGROUND

TERMS & DEFINITIONS

What is MID-LIFT®?

DESIGN and INSTALLATION. These two simple perspectives of rocker arm function must be understood separately. Because you can have one and not the other. If the "design geometry" isn't correct, then your "installed geometry" can only be set for the lesser of two evils, either setting the pivot points for a MID-LIFT relationship on the "valve" side of the rocker arm, or the "push rod" side of the rocker. Not both. On a stud mounted system, this is done by changing the pushrod length. On a stand (shaft) system, this is done by adjusting the stand's height.

From the above two perspectives we establish that there are TWO kinds of geometry:

The first is: "Design Geometry™."

The second is: "Installed Geometry™."

Understanding the difference between DESIGN and INSTALLED geometry is one good example; and it is not only critical in choosing the right parts for your engine, but also installing them correctly.

All Over-Head Valve (OHV) engines have pushrods that link the cam and tappet information to the rocker arm. The rocker arm pivots about an axis upon the cylinder head, being pushed up by the pushrod, so that the opposite end of the rocker arm pushes down upon the tip of the valve. This is really "engines 101" -- but it's worth placing in perspective for our novice readers. As stated elsewhere, there are two other perspectives that need to be understood, in addition to what we call "design geometry" and "installed geometry." These other two perspectives refer to the differences in operating characteristics of the components we just spoke of. The "cam" is a rotating device, with an eccentric lobe to it, that allows anything sitting upon it to be pushed up as it rotates. This is an over simplification that is really very precise and exact in its operating characteristics. But this basic fact is true. The component that rides upon it is known as a "tappet" or "lifter" or "cam follower," depending on who's talking. Each term have their roots in the American language of engine talk, but the part is the same. Riding upon the cam follower, is the pushrod. Then the rocker arm, and finally the "valve" of our "valve train." Everything, except the cam and the rocker arm, are linear in their operating characteristics. They basically follow an in-line path. But the cam and the rocker arm are "radial" and rotate about an axis. Actually, the rocker arm doesn't rotate, it reciprocates (stops and reverses itself); but none-the-less it follows around an axis, and this has mechanical characteristics that must be understood to design and install it properly on the engine with these linear components.

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MILLER MID-LIFT
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