The
other companies designed their rocker arms in a "closed valve" state, with
regard to only fitting the head,
not
the engine, thus disregarding the pushrod's influence with the valve. What Jim
Miller did that was novel, was to design the rocker arm's tangent points when BOTH the valve and the
cam were in the MID-LIFT position simultaneously. This
influenced all of the critical dimensions and equally divided the rocker arm's
circular motion (arc) on BOTH sides, which Jim emphasized was critical to not
only minimizing
back-and-forth sweep atop the valve, but providing the maximum information of
the cam dynamics to the rocker arm with the ultimate least amount of wasted motion.
This additional motion, found in all previous rocker manufacturers, required the
crank to turn additional degrees of rotation to effect the same amount of cam
lift "at the rocker arm."
The obvious side effects that
inherently go with this over-arcing (or under-arcing) motion are varying degrees
of additional and unnecessary friction and heat, imposed on the valve stem,
valve guide, valve tip and even the pushrod ends. In more extreme misalignments
the tappet body in the block is forced against the bore wall with increased
pressure imposed from a pushrod moving in and out way more than it needed,
whipping into excessive (and unnecessary) harmonics that are on the receiving
end of increased spring pressures multiplied by the rocker's ratio. But in 1973,
no one, looked at these factors being caused by "geometry," they were summarily
dismissed as symptoms to increased valve lifts, valve springs and cam rates;
when in fact -- it was this bad geometry that exaggerated the need for these
increased valve train changes, because that information was being lost in the
translation.
Jim Miller's MID-LIFT principle of design set in stone a
formula that would apply to any valve lift,
provided the engine builder set the "installed geometry" for the net valve lift
of the engine, a mandatory task with any rocker. Finally, a standard! And in
1974, the phrase Jim kept using was coined: "Mid-Lift" becoming the terminology
to a Patent application in 1978, that was filed in 1980 and issued in 1982.
The
MID-LIFT Patent: #4,365,785.
As much as some would like to say
this was common knowledge in Europe, or anywhere else at some other time in
history before 1973, or that the MID-LIFT solution was used or thought of before
(as some blogs have suggested), IT WASN'T. And that is why, the MID-LIFT Patent
was issued, which included International searches to qualify.
How
could this be, how could an industry of multi-million dollar cam companies make
such an oversight? When you're 20 years old, it's hard to appreciate the value
of such a discovery, especially if you don't know how it was missed. Finding the
answer to this confounding question became necessary. Within a year the answer
would be known.
In 1958, Harland Sharp, an
avid automotive enthusiast and hard working, innovative machinist, took a
standard OEM stamped steel "shoe" type rocker arm and laid it on its side to
trace its silhouette on a piece of paper. Knowing he wanted to place a roller
tip on the end, he traced a roughly .600" diameter roller, placing the bottom of
the roller's diameter on the same horizon as the shoe's contact pad of the
original rocker arm. This was the mistake. He marked a center to this circle for
the location of the roller pin, then using a scribe, he transferred his
silhouette to a block of aluminum where he proceeded to machine his roller tip
rocker body. Several years later, Harvey Crane asked Harland to make roller
rocker arms for his company: CRANE CAMS. However, within a short period of time,
Crane's excellent national marketing outstripped Harland's production
capability, forcing CRANE to use other sources, eventually making them in-house.
Having already established an identity with Harland's roller rocker arms, CRANE
simply kept the same design basics which Sharp had been using, and the mistake
was copied. During the 1960's, several of today's top cam companies began making
their own line of rocker arms, and although many would no doubt argue that their
design was unique to their own ideas, the fact of the matter is: that same
mistake appears to have been copied throughout the industry... and except for
some copy-cats pretending they have a "better geometry," it continues to
this day. True story!
^
