Page 3 - Along the Way December 2020
P. 3
FORMANCE PUSHROD TECHNOLOGY
BY MIKE MAVRIGIAN
ABOVE: A straight pushrod tends to exhibit directional deformation at the center area, as shown I this 5/16” example (with highest deflection in red).
BELOW: Adding mass to the lifter end, as shown in this example of COMP’s adjustable pushrods, decreases directional deformation substantially.
(Illustrations courtesy COMP Cams)
looser than normal just to allow for the one of two shims, and top sections are upper pushrod tip can aid in providing
valves seats to settle. available in 0.200” increments for course additional high-lift clearance. Some
adjustment. According to COMP, the builders prefer to convert to a ball-cup
The new XD-A shim adjustable XD-A pushrods provide a 90% Increase at the rocker tip (obviously requiring
pushrod system incorporates a new in bending stiffness comparing the 5/16- adjustable ball-stud rockers) in order
patent pending system to give the 7/16 XD-A to a standard 5/16 x 0.080” to retain more oil at the pushrod upper
accuracy and durability of direct OHC wall pushrod. tip during high engine speeds. Cup
pill under bucket style adjustments inside style pushrods can be formed into the
a slide-together multi-piece pushrod A discussion of pushrod ball tips is in pushrod, or as inserts, sometimes with
design. Simply remove the pushrod and order. While 180-degree ball ends have the insert featuring bronze or a copper
change shims to set the required lash or been the norm, with a move to higher alloy for extreme RPM levels. Adjuster
preload. Shims are currently available valve lift, interference at the rocker balls always need to be harder than the
in 0.004” increments and can easily be arm may occur. A more generous tip cup material. Cup-equipped pushrods
sanded in a figure 8 pattern for extremely radius (210 degree offered by Trend, often feature a somewhat shallow radius
fine adjustment. for example) can provide additional to benefit rocker arm clearance. The
operational clearance at the rocker range of available pushrod tip materials,
Applications include any pushrod pushrod cup under more severe rocker profiles and radii is extensive to suit a
operated engine, and especially relevant arm angle. The extended tip radius variety of applications, including both
in GM Gen III through Gen V small provides a bit of under-ball contact to oil-through and solid designs for street
block V8’s, including LS1, LS3, LS7 and accommodate severe arm angle during through all types of racing applications.
new LT engines, with their low mass full-lift transition. For rockers that For example, according to Trend,
rocker arms and light valvetrain. One feature adjustable ball-tipped studs, applications for Top Fuel and Funny
set of Pushrods can be adjusted over a a relatively shallow cup radius at the
0.232” range in 0.004” increments using
72 JULY-SEPT 2018 engine professional
BY MIKE MAVRIGIAN
ABOVE: A straight pushrod tends to exhibit directional deformation at the center area, as shown I this 5/16” example (with highest deflection in red).
BELOW: Adding mass to the lifter end, as shown in this example of COMP’s adjustable pushrods, decreases directional deformation substantially.
(Illustrations courtesy COMP Cams)
looser than normal just to allow for the one of two shims, and top sections are upper pushrod tip can aid in providing
valves seats to settle. available in 0.200” increments for course additional high-lift clearance. Some
adjustment. According to COMP, the builders prefer to convert to a ball-cup
The new XD-A shim adjustable XD-A pushrods provide a 90% Increase at the rocker tip (obviously requiring
pushrod system incorporates a new in bending stiffness comparing the 5/16- adjustable ball-stud rockers) in order
patent pending system to give the 7/16 XD-A to a standard 5/16 x 0.080” to retain more oil at the pushrod upper
accuracy and durability of direct OHC wall pushrod. tip during high engine speeds. Cup
pill under bucket style adjustments inside style pushrods can be formed into the
a slide-together multi-piece pushrod A discussion of pushrod ball tips is in pushrod, or as inserts, sometimes with
design. Simply remove the pushrod and order. While 180-degree ball ends have the insert featuring bronze or a copper
change shims to set the required lash or been the norm, with a move to higher alloy for extreme RPM levels. Adjuster
preload. Shims are currently available valve lift, interference at the rocker balls always need to be harder than the
in 0.004” increments and can easily be arm may occur. A more generous tip cup material. Cup-equipped pushrods
sanded in a figure 8 pattern for extremely radius (210 degree offered by Trend, often feature a somewhat shallow radius
fine adjustment. for example) can provide additional to benefit rocker arm clearance. The
operational clearance at the rocker range of available pushrod tip materials,
Applications include any pushrod pushrod cup under more severe rocker profiles and radii is extensive to suit a
operated engine, and especially relevant arm angle. The extended tip radius variety of applications, including both
in GM Gen III through Gen V small provides a bit of under-ball contact to oil-through and solid designs for street
block V8’s, including LS1, LS3, LS7 and accommodate severe arm angle during through all types of racing applications.
new LT engines, with their low mass full-lift transition. For rockers that For example, according to Trend,
rocker arms and light valvetrain. One feature adjustable ball-tipped studs, applications for Top Fuel and Funny
set of Pushrods can be adjusted over a a relatively shallow cup radius at the
0.232” range in 0.004” increments using
72 JULY-SEPT 2018 engine professional
