INSTALLED Geometry™,
is the art of adjusting the rocker's axis below the roller tip
centerline, exactly HALF of whatever the NET valve lift is. Here is the
illustration that Jim Miller published in magazines several years before
he used it in the 1988 Lunati catalog, where it remained for 12
years. With the valve closed, the two key measurements to the upper LEFT take reference from the valve spring
retainer and together create a "STACK
HEIGHT" which
is then measured in comparison to the trunnion's centerline
to establish the "ROCKER HEIGHT".
When set properly, this height will be HALF of
your NET Valve Lift, as measured in the CLOSED VALVE position.
By using the VALVE
SPRING RETAINER as a reference plane, you can run a machinist ruler (or
similarly accurate tool) along the side of the trunnion, to find the
trunnion's axis. Whatever your NET valve lift is, then HALF of that
should be the amount which the trunnion sits below the ROLLER PIN'S
AXIS. By measuring the amount which the valve tip extends above the
retainer's top, then dividing the Roller in half and adding it to this,
you get the
STACK
HEIGHT (the height of the roller pin axis above the
retainer). As shown in the illustration above, the
ROCKER HEIGHT is the
SUM of the stack height and whatever the dimension of the trunnion's
axis is above, or below, the retainer's top plane. PLEASE NOTE: This
illustration makes a reference to the TIP HEIGHT, showing it (logically)
above the valve spring retainer. But this term is a specific dimension
used in another way. (See:
DEFINITIONS
or Valve TIP
HEIGHT)
On STAND MOUNTED
SYSTEMS (also known as "shaft systems"), the same reference between
the SHAFT Centerline and the ROLLER TIP Centerline is relevant. But with
differing valve lifts between the Intake and Exhaust valves of designs
with a common shaft for two or more rocker arms, individually moving the
rocker height for setting as shown above is not possible, but it is
still necessary to avoid wasted motion with one rocker arm or the other.
So what do you do? See:
VALVE TIP ADJUSTMENT. For another method we use on stand systems,
with clear illustrations you can ZOOM in on, click below:
