Page 1 - Along the Way December 2020
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Evolving designs improve valvetrain stability
BY MIKE MAVRIGIAN
Example of a Manton pushrod The heavier (larger diameter) steel pushrods
with tapered ends. The pushrod are favored by many, where the tradeoff
hardened ball end (black tip) in OHV of additional weight vs strength and
engages the rocker. systems rigidity makes sense in order to reduce
The heavier end engages is often the the potential of flex. Pushrod flex induces
the lifter. The tapers provide weak link in frequencies that are transmitted through
added clearance for high-lift a high-revving, the valvetrain. This results in instability
applications. high-lift and high which can cause the rocker tip to
spring pressure oscillate, dancing around the rocker cup
68 JULY-SEPT 2018 engine professional application. The entire or adjuster ball instead of maintaining a
valvetrain is subjected to potential consistent center contact, in addition to
harmonics and valve spring frequencies. cam timing fluctuation.
In an OHV engine, pushrods play a
major role with regard to valve spring Pushrod taper (one end or both)
dynamics, valve stability and valve allows use of a thicker center or lower
bounce. mass for added strength along with
Pushrod stiffness is a critical issue. providing clearance (where needed) for
When pushrods flex under extreme rocker arm, and where required, for lifter
springs loads and high lift conditions, clearance and pushrod-to-head as well.
the flexing can interrupt the transition Elgin’s one-piece tapered-end pushrods
of dynamic force between the lifter and (referred to as swedged ends) feature
valve, to the point where it can result a short taper at each end, providing
in erratic and somewhat late camshaft additional rocker arm and lifter clearance
timing. The quick transition from a no- while maintaining a straight profile along
load (at the base circle lash setting) to the rod body. Increases in intake runner
peak stress approaching full lift, where volume, common in aftermarket cylinder
spring pressures are highest, with more heads, often create pushrod clearance
intense loads at the exhaust pushrod issues, prompting the need for tapered
as higher cylinder pressure must be pushrods where diameter is decreased
overcome. While conventional thinking in the upper body but increased in
routinely dictates that we should attempt the lower section in order to increase
to reduce valvetrain component weight, stability at the lifter end. This allows the
manufacture to maintain a larger body
Evolving designs improve valvetrain stability
BY MIKE MAVRIGIAN
Example of a Manton pushrod The heavier (larger diameter) steel pushrods
with tapered ends. The pushrod are favored by many, where the tradeoff
hardened ball end (black tip) in OHV of additional weight vs strength and
engages the rocker. systems rigidity makes sense in order to reduce
The heavier end engages is often the the potential of flex. Pushrod flex induces
the lifter. The tapers provide weak link in frequencies that are transmitted through
added clearance for high-lift a high-revving, the valvetrain. This results in instability
applications. high-lift and high which can cause the rocker tip to
spring pressure oscillate, dancing around the rocker cup
68 JULY-SEPT 2018 engine professional application. The entire or adjuster ball instead of maintaining a
valvetrain is subjected to potential consistent center contact, in addition to
harmonics and valve spring frequencies. cam timing fluctuation.
In an OHV engine, pushrods play a
major role with regard to valve spring Pushrod taper (one end or both)
dynamics, valve stability and valve allows use of a thicker center or lower
bounce. mass for added strength along with
Pushrod stiffness is a critical issue. providing clearance (where needed) for
When pushrods flex under extreme rocker arm, and where required, for lifter
springs loads and high lift conditions, clearance and pushrod-to-head as well.
the flexing can interrupt the transition Elgin’s one-piece tapered-end pushrods
of dynamic force between the lifter and (referred to as swedged ends) feature
valve, to the point where it can result a short taper at each end, providing
in erratic and somewhat late camshaft additional rocker arm and lifter clearance
timing. The quick transition from a no- while maintaining a straight profile along
load (at the base circle lash setting) to the rod body. Increases in intake runner
peak stress approaching full lift, where volume, common in aftermarket cylinder
spring pressures are highest, with more heads, often create pushrod clearance
intense loads at the exhaust pushrod issues, prompting the need for tapered
as higher cylinder pressure must be pushrods where diameter is decreased
overcome. While conventional thinking in the upper body but increased in
routinely dictates that we should attempt the lower section in order to increase
to reduce valvetrain component weight, stability at the lifter end. This allows the
manufacture to maintain a larger body
