With
the valve spring and all the measuring lines removed, we can see the
real line that is important. The WHITE LINE running between
the trunnion (or shaft) center and the roller pin axis is what we've
always referred to as the "motion line." This line is what you are
really adjusting the angle of when raising and lowering the rocker
body in relation to the valve tip. What is important to see here, is
the 11-1/3° angle between the STUD and the VALVE. As the two white
arrows depict, the more you increase the valve tip height (upward),
the shorter the distance between the stud and valve becomes, so the
more the rocker arm's roller will move across the top of the valve
when sitting in the closed valve position as shown here. What is important
is the angle of this motion line when the valve is
closed. But we measure this by "height." If you follow the bad
advice of those who tell you that correct geometry is placing the
roller in the middle of the valve, then this angle changes based on
varying valve tip and rocker design combinations that are impossible
for any component manufacturer to predict or control, unless they
make everything.
It makes no difference where the roller
is sitting atop the valve, as long as its foot print of motion stays
on top of the valve. What matters is the "angle of motion" as the
rocker moves this MOTION LINE (rocker loads) from closed valve, to
mid-lift, to full-lift. As long as the angle when closed begins with
half of the angle of motion (i.e., 12° to MID-LIFT for 24° of
full motion), then these loads will balance in a straight down
direction upon the valve, and NOT be over-arcing and shoving the
valve against the guide, causing excessive friction, heat, wear
and horsepower loss. (See:
DEFINITIONS
or Valve TIP
HEIGHT)
