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Column strength, in engineering terms, refers to the ability of a structural element to withstand compressive forces without buckling. For pushrods, which essentially work in compression during engine operation, high column strength is vital. This strength ensures that the pushrods maintain their structural integrity and dimensional stability under the varying loads experienced during engine cycles. Insufficient column strength can lead to bending or buckling of the pushrod, which in turn can cause loss of power from reduced valve lift, and in extreme cases engine damage.

When considering pushrod column strength there are two main things we want to ask. First how strong does my pushrod need to be? And second, What factors can we change to make the pushrod column stronger.

This first question is a hard one to answer as their isn’t a clear marker to know when your pushrod is “strong enough”. There are however a few major factors that increase the need for a stronger pushrod, being: spring pressure, rocker arm ratio, the aggressiveness of the camshaft, and the pushrod angle. The spring pressure refers to the force exerted by the valve springs. Higher spring pressure demands more strength from the pushrod to resist the forces trying to compress it. This is amplified by the rocker arm as its ratio multiplies the spring force being channeled through it. Furthermore, the aggressiveness of the camshaft, in conjunction with the RPM increase the dynamic loads on the pushrod. lastly and often not considered, the pushrod angle. Increasing the angle of the pushrod increases the amount of load that the pushrod has to support. This is because the pushrod can only push along its axis so if the lifter isn’t in line with the pushrod it also has to add a sideways force to make it so that it pushes directly up the pushrod.

To address the second question regarding enhancing pushrod column strength, several factors can be modified, including diameter, wall thickness, heat treatment, and taper. When narrowing down which factors to use, you will generally want to first select the largest diameter pushrod that fits. Then, increase the wall thickness until you believe the pushrod has adequate strength. If you still do not think the pushrod is strong enough with the thickest wall, we can perform an additional heat treatment on the tube to increase its strength. If more strength is needed and the diameter of your pushrod is limited at one or both ends, we can taper the pushrod, reducing the outer diameter only where necessary. As a last resort, and if you do not require through-oiling in your pushrod, we can upgrade the material of the pushrod to S-7 tool steel, providing ultimate rigidity and impact resistance.

Pushrod Deflection & COmpression diagrams

Note: In this simplified illustration, you can see that pushrod deflection and compression can cause reduced net valve lift, the result of a foreshortened pushrod. Valve timing (duration and timing) can also be affected by inadequate pushrod stiffness.

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