3-piece design:
Before diving into the reasons for our focus on modular pushrods, it's essential to understand the role of a pushrod. Simply put, pushrods channel energy from the lifter to the rocker arm. If mismatched, they can cause engine failures due to inappropriate valve timing and lift. The right pushrod ensures maximum horsepower and increased valve train durability.
Choosing the right pushrod involves considering its length, diameter, wall thickness, materials, heat treatment, and end configurations tailored to the specific engine. Though it might seem straightforward, several factors come into play. That's why we specialize in crafting custom modular pushrods:
Compatibility & Diversity: The ends of the pushrod need to work seamlessly with other components. This demands materials that double as bearings while being highly impact-resistant. Additionally, it paves the way for a vast range of tip designs.
Flexibility & Performance: Modular pushrods grant the liberty to select distinct tapers for clearance. Alterations in wall thickness, diameter, and tube taper influence the pushrod's natural frequency.
Material & Durability: The pushrod's column, distinct from its ends, should possess the strength to endure the rigors of high engine speeds and cylinder pressures. By opting for a different material from the pushrod end, we can freely choose the heat treatment. Typically, we use the robust 4130/4135 tubing. For our Series 2 & 4, we apply the MeloniteTM process for wear resistance and durability. In our Series 5, a special heat treatment elevates the material's Rockwell hardness increasing its resilience. We also have a variant made of heat-treated solid bar S-7 tool steel, the same as high-quality chisels and hammers, perfect for extreme scenarios.
The only way to not compromise in these three arias is to make a modular pushrod, Optimizing the tips and center section so that each can do its job as well as possible.
Tip selection
Selecting the right pushrod tip is straightforward but crucial. An incorrect choice can lead to pushrod failure. There are three main factors to consider: shape and size, material of the tip, and the requirement for oil transfer.
Shape and Size: The shape and size of the pushrod tip are largely determined by the rocker arm and lifter. For example, if your rocker arm has a 5/16” diameter cup, you'll need a pushrod with a 5/16” diameter ball to match. With certain tips, like the 5/16 ball tip, extended length tips are available, which are beneficial for clearance issues, particularly in applications with offset lifters.
Material Matters: The tip material can be customized for your specific needs, often on the rocker arm side of the pushrod. Our standard material is 8620-bearing steel, but it's recommended to upgrade to tool steel if your rocker arm has a tool steel cup. This is crucial because in a ball and cup bearing interface, the ball should not be softer than the cup. A softer ball can wear unevenly and eventually fail. Conversely, a harder ball ensures the cup wears into a more rounded shape, improving the bearing surface over time. You may also choose to upgrade the tip material if additional strength, survice life or heat resistance is necessary.
Oiling Through the Pushrod: To determine if you need a thru-oiling pushrod, check if your previous pushrod has a hole running through its length. In a valve train system, each bearing segment needs lubrication, either by splash feed or direct pressure feed. In a pressure-fed system, oil is typically fed into the lifter or the rocker arm stand, and passageways in each component disperse the oil around the valvetrain. The thru-oiling pushrod is essential for transferring oil from the lifter to the rocker arm or vice versa.
Tube selection
Choosing the right center section of a pushrod involves understanding four crucial aspects: diameter, surface treatment, wall thickness, and heat treatment. The first two aspects are typically influenced by your cylinder head and rocker arm design, while the latter two hinge on the performance demands placed on the pushrod.
Diameter and Surface Treatment: When using a guide plate in your valvetrain system, it's essential that the pushrod's diameter matches the specifications of the guide plate. Additionally, the pushrod should have a hardened surface to prevent damage or wear from the guide plate. This surface treatment should not be confused with the core heat treatment process to be discussed later. In systems without a guide plate, surface hardness becomes no longer critical, and the pushrod's diameter is often constrained by the dimensions of the cylinder head’s pushrod port hole or lifter body. Keep in mind that the permissible diameter might vary from cylinder to cylinder, and a pushrod that fits at base circle might encounter issues at different points in the lift cycle. While specifics on pushrod diameter can be found in the Strength, Frequency, and Weight sections, a general recommendation is to opt for the largest diameter feasible for your setup, Leaving at least .030” clearance between the pushrod and its closest interference point.
Wall Thickness and Heat Treatment: These factors largely depend on the load experienced by the pushrod. In scenarios where the pushrod is subject to higher loads – such as from boost, nitrous, increased rocker arm ratios, or higher spring pressures – enhancing wall thickness and improving heat treatment quality can be beneficial. The interplay between these two aspects and the overall strength of the pushrod is elaborated in the "Strength" section of this page.
Length
For complete instructions on selecting the right pushrod length, our “Determine Diameter & Length” page has all the details you need. A detail often not considered is the impact of the flat ends on the pushrod. These ends can slightly alter the effective length of the pushrod. This detail is important because there isn't a standard size for these flat ends across the industry. Even if two pushrods from different manufacturers seem the same length, they might not function identically due to this variation. Typically, the difference is small, usually less than 0.010 inches, but it's worth noting.
To ensure you choose the correct length, using one of our pushrod length checking tools is the best approach. These tools are precisely calibrated to mimic the final fit of our pushrods, giving you an accurate measurement.
Taper
Tapering a pushrod is not a standard requirement and should generally be avoided unless necessary. In high horsepower engines, if you find that a larger pushrod can fit everywhere except one or two narrow areas, tapering the pushrod at these specific sections could be beneficial.
To get the best tapered pushrod it is crucial not to simply reduce the diameter at these narrow points. Instead, the pushrod should be gradually tapered from one or both ends. This method helps avoid any sudden changes in diameter, which could lead to stress concentration points. Such points are problematic because they can significantly increase the risk of the pushrod fracturing under stress.
Strength
As the load on a pushrod increases, it will compress more until it reaches a certain load level. At this point, the pushrod begins to bend, forming a C or S shape. Once bending starts, a small additional load can cause significant compression. It's crucial to consider the pushrod's strength both before and after this bending, or buckling, occurs.
Pre-Buckling Strength: The strength of the pushrod before it buckles depends roughly equivalently on its length, cross-sectional area, and the material's inherent stiffness. Often, the length of the pushrod is a fixed parameter, so the focus shifts to the material and cross-sectional area for added strength. Enhancing the cross-sectional area can be achieved in two ways: by increasing the outer diameter of the pushrod tube or by thickening its walls. We use pre-hardened seamless 4135 chromoly tubing for most of our pushrods due to its exceptional material characteristics. For further improvement, we can re-heat-treat the tube to increase stiffness. In extreme cases, we offer pushrod center sections made from solid tool steel rod, undergoing a multi-stage heat treatment for maximum.
Post-Buckling Strength: The strength of the pushrod after buckling relates to the load level at which buckling begins. Increasing this critical buckling load is key to enhancing post-buckling strength. This improvement is approached similarly to pre-buckling strength enhancement, but each aspect of the pushrod has a different importance. The critical buckling load is influenced in the following way: approximately one part material, two parts length, and four parts outer diameter. The impact of wall thickness is variable but is almost always less significant than the outer diameter.
For standard applications, we recommend selecting the largest diameter pushrod that fits your setup, as it offers the most significant benefits. Depending on your specific needs, upgrading the heat treatment or wall thickness might be the next step. For high RPM engines, better heat treatment is advisable, while in other scenarios, a thicker wall may be more beneficial. In very high-performance applications or where only long, slender pushrods can be accommodated, we suggest a heat-treated, heavy-wall pushrod.
Weight
The importance of pushrod weight in a valvetrain system is often over emphasized, however it is essential to understand its impact. The weight, or more accurately, the mass of the pushrod, plays a role in how the valvetrain behaves during each valve opening event. This process involves the valvetrain being pushed in two directions before coming to a stop: first by the lifter to open, then by the valve spring to close, and finally, it's slowed down by the lifter again. The force required by the spring and lifter is partly dependent on the pushrod's mass. Increased mass means the spring and lifter need to exert more effort to move the valvetrain.
The lifter usually manages to provide the necessary force to open the valve, but the spring's capacity to push is limited. A key question in managing valvetrain mass is whether the spring can close the valve quickly enough during operation. At a certain RPM, the inertia may become too great for the valve spring, causing the lifter to lose contact with the camshaft, leading to reduced component life and power loss. If this issue occurs within your engine's intended RPM range, lightening the valvetrain or even better using a stiffer spring would be beneficial. However, if it happens outside the intended RPM range, pushrod weight is less critical compared to stiffness.
Understanding pushrod weight also involves recognizing how different components influence the overall affective mass of the valvetrain. There are three main categories: the pushrod side, the rocker arm, and the valve side. The valve and its components directly affect the mass seen by the spring. The influence of the rocker arm on valvetrain mass is detailed on our rocker arm technical information page. Lastly, the pushrod and lifter have a lesser impact on the affective mass due to their slower movement, influenced by the rocker arm ratio. The relationship between pushrod and valve mass involves dividing the pushrod mass by the square of the rocker arm ratio, indicating that higher rocker arm ratios diminish the significance of pushrod weight.
Some may argue that heavier pushrods increase component wear due to higher forces. While this can be true, it's important to note that lighter pushrods are often weaker, leading to more flex and higher impact loads at each bearing surface, which can cause significantly more wear.
Frequency
Every part of the valvetrain, including the pushrod, has a natural frequency. When a component is exposed to vibrations matching this frequency, it vibrates intensely. In the valvetrain, this intense vibration can lead to valve float or even damage parts of the valvetrain. The most effective strategy to prevent this for the pushrod is to increase its natural frequency as much as possible. This way, the engine's RPMs stay well below the pushrod's natural frequency, reducing the risk of these harmful intense vibrations.
To elevate the natural frequency of a pushrod, its stiffness needs to be enhanced. Shorter pushrods with larger diameters and hardened materials exhibit the highest natural frequencies. By focusing on these characteristics, the pushrod can be optimized to perform efficiently and safely at higher engine speeds, protecting against vibration-induced damage.
