Valve Train Geometry
Valve Train geometry is
when the rocker arm tip
moves from the intake
side of the valve stem
tip, across the center
of the tip (at
approximately mid lift),
to the exhaust side of
the valve stem tip (at
full lift) and back.
(SEE Diagram A)
Measuring Pushrods:
Pushrods lengths are
measured starting at
0.140 gauge diameter,
which means if you start
at the center of the
ball end and measure
0.070 in each direction
(totaling .0140) then
wherever this distance
intersects with the
radius of the pushrod is
where the measurement is
actually started. (SEE
Diagram B) The rate of
the radius will affect
the overall actual
length of the pushrod.
The reason for choosing
this measuring standard
is that some
manufactures have larger
or smaller holes with
different chamfers, and
these factors will
change the measured
length.
Two pushrods with the
same actual 0.140 gauge
diameter lengths but
manufactured by
different vendors may
show different lengths.
How to verify
your required pushrod
length
Before starting it is
important that you make
sure that the lifters
you are going to use for
determining pushrod
length are pumped up.
Start out using an
adjustable pushrod that
has a length close to
the size you think you
are going to need. Next
bring your number one
cylinder to TDC (Top
Dead Center), install
the adjustable pushrod,
while making sure that
the tip of the rocker is
riding in the center of
the valve stem tip take
up all the slack between
the pushrod and the
rocker tip, you will now
be @ 0 lash or very
close. Once you have
done this adjust the
preload on the lifter
(hydraulic) to the
amount that you want to
run making sure that the
rocker tip ends up
staying in the center of
the valves tip. If not
you may need to remove
the preload, slightly
lengthen the pushrod and
repeat the process until
you have the rocker tip
is riding in the center
of the valves tip with
the amount of preload
you are wanting to run.
Once this is achieved
remove the pushrod
carefully so that you do
not alter the length you
have & take an overall
measurement.
