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04EB_16Dakota 4/7/16 11:30 AM Page 1motion from the camshaft’s lobe to
the valve. e pushrod’s length, wall
thickness and end con guration,
along with the material it’s made of,
are all speci c to the application. Like
valve springs, there’s nothing overly
fancy about pushrods, but they are
an essential element of the engine’s
design, reliability and performance.
Pushrods are required to transmit
the reciprocating motion of the valve
lifter to the rocker arm. Both ends
of the pushrod form a connection,
which accommodates the angular
movements of the pushrod in
response to the straight-line motion
of the lifter barrel on one side and the
arc motion of the rocker arm on the
other.
Since the pushrod is part of the
valvetrain, it’s exposed to vibration
and shock from the opening and
closing of the valve against extreme
coil spring pressure. Due to the
energy necessary to open the closed
valve at a fast rate, the pushrod has
to endure excessive force while still
accurately transferring the motion
created by the camshaft pro le.
Today’s pushrods are strengthened
in critical load-bearing areas and
utilize a number of design features in
application-speci c uses such as: one-
piece pushrods made from chrome
moly and tool steel; bronze-insert,
chrome-moly pushrods; double-
tapered, 7/16th pushrods that are
case-hardened; straight, double-taper
or o set-taper con gurations; and
standard and tapered pushrods in
varied wall thicknesses.
Due to di erences in engine
design, pushrods can vary in length.
e pushrod’s length, along with
the rpm potential of the engine, are
critical design factors.
“When rebuilding an engine,
especially if using non-stock parts or
milling the deck or heads, you should
choose a pushrod length that preventsthe rocker arm slot from bottoming
out when either in the closed or open
valve position,” Gathman says. “If
the pushrod is too short, you’ll face
improper valve opening, rocker slot
wear and stud wear. If the pushrod
is too long, you can break the rocker
when it bottoms out in full lift
position.”
If you’re upgrading the camshaft
and springs in your engine, you’ll
want to switch from a stock pushrod
to a hardened pushrod.
“Follow OE recommendations
to start. Higher RPMs and valve
spring loads will need more sti ness
and strength, which means better
materials, larger diameter and
increased wall thickness,” says
Elgin’s Brier Dieckman. “ en, take
into account any changes to the
camshaft or other components.”
When it comes to pushrod
diameter, it’s usually best to use
the biggest diameter you have
clearance for. is gives you added
strength and sti ness. If clearance
is an issue, going to a thickerpushrod wall can help with both as
well, according to Dieckman.
“ e best material is 4130 aircraft-
quality seamless chrome-moly,”
Dieckman says. “ is is available in
our Elgin PRO-STOCK 700 Series
performance pushrods and our
PRO-STOCK one-piece thick-wall
pushrods. Our one-piece pushrods
o er up to 40% greater column
strength and increased sti ness to
virtually eliminate the compression
and de ection that can lead to valve
oat and possibly catastrophic failure.
ese pushrods also are centerless
ground, have fully hard-turned
210-degree radius ends and are black
oxide coated.”Conclusion
Manufacturers are readily available
to ensure you pick the appropriate
parts for your engine every time. Just
keep in mind your application, your
rpm range and horsepower goals. e
valvetrain puzzle falls into place from
there. EB40-43 eb.aug20 Valvetrain.indd 43 8/7/20 8:32 AM
Naresh Jariwala