Free Guide to Measuring Pushrod Length for Engines

Understanding Pushrod Length and Why It Matters

Pushrods are cylindrical metal components that transfer motion from a camshaft to the rocker arms in an engine's valve train. In overhead valve (OHV) engines, pushrods play a critical role in opening and closing the engine's intake and exhaust valves at precisely the right moments during the combustion cycle. The length of these pushrods directly affects how well your engine functions, making accurate measurement essential for anyone rebuilding or modifying an engine.

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When a pushrod is the wrong length, several problems can occur. If a pushrod is too long, it can cause excessive valve lash—the gap between the rocker arm and valve stem. This creates a knocking sound and prevents valves from closing completely, leading to poor compression and power loss. If a pushrod is too short, it creates the opposite problem: the rocker arm may not fully open the valve, restricting airflow into and out of the cylinders. Both scenarios reduce engine performance, increase fuel consumption, and can cause premature wear on valve train components.

Pushrod length varies significantly depending on the engine type, manufacturer, and specific application. A small-block Chevrolet 350 engine typically uses 7.800-inch pushrods, while a big-block Chevrolet 454 may require 8.120-inch pushrods. Ford engines, Mopar engines, and other manufacturers each have their own specifications. Some performance modifications, such as installing different cylinder head castings or a taller intake manifold, may require custom pushrod lengths.

Understanding your engine's pushrod length requirements prevents costly mistakes during engine assembly. Incorrect pushrods can cause valve damage, reduce power output, and create expensive problems that only become apparent during engine startup or operation.

Practical Takeaway: Before measuring or selecting pushrods, locate your engine's original specification sheet. This documents the correct pushrod length for your specific engine configuration and serves as a reference point for all measurements.

Tools and Materials You'll Need for Accurate Measurement

Measuring pushrod length accurately requires specific tools. While the process isn't complicated, using the right equipment ensures your measurements are reliable. The primary tool you'll need is a quality ruler or measuring tape marked in increments of at least 1/16 inch. Many engine builders prefer dial calipers or digital calipers, which provide measurements to the nearest 1/32 inch or even smaller increments. A steel ruler at least 12 inches long works well for basic measurements, though precision measuring tools deliver better accuracy.

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Beyond measuring devices, you'll need access to your engine's cylinder head and block. If you're measuring an existing pushrod, you can measure it directly. If you're determining what length you need, you'll need to measure the distance from the pushrod seat on the block to the pushrod hole on the cylinder head. This requires the block and head to be properly positioned and aligned as they would be during normal engine assembly.

A straight edge—a perfectly flat metal bar or ruler—helps ensure accurate measurements between the block and head. The straight edge prevents measurement errors caused by curved or uneven surfaces. A small level helps confirm that components are properly aligned during measurement, ensuring the distance between mounting points is truly vertical.

When measuring existing pushrods, place them on a flat surface such as a machinist's layout table or flat workbench. Avoid measuring on soft surfaces that might compress under the pushrod's weight. For new pushrod selection, having your engine's service manual or specification sheet available helps confirm the measurement requirements for your specific engine.

A notebook for recording measurements prevents confusion when you have multiple measurements to track. Document the pushrod size, which cylinders the pushrods came from, and any notes about their condition. This information becomes valuable if you need to reference measurements later or if you're working with multiple engine configurations.

Practical Takeaway: Invest in a quality dial caliper (typically $15-40) rather than relying solely on a ruler. The improved precision pays dividends in pushrod selection accuracy and prevents problems that would cost far more to fix later.

Measuring Existing Pushrods in Your Engine

If you're removing pushrods from an existing engine for measurement or replacement, the process is straightforward. First, remove the valve cover from the cylinder head. This exposes the rocker arms and the tops of the pushrods. Carefully remove the rocker arm bolts or studs—typically three to five bolts per rocker arm. Document which rocker arms came from which cylinders to maintain organization, as different cylinders may sometimes use different pushrod lengths if the head or block has been modified.

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Once the rocker arms are removed, the pushrods can be lifted out of their bores. Handle them carefully to avoid bending them, as bent pushrods will produce inaccurate measurements. Place each pushrod on a clean, flat surface. A piece of glass or a machinist's layout table works well. Never measure a pushrod while it's sitting on a soft surface like a workbench covered with cloth, as the surface may compress slightly and affect accuracy.

Measure the entire length of the pushrod from one end to the other using your dial calipers or measuring tape. For calipers, place one tip at the very end of the pushrod and close the caliper until it contacts the opposite end. Read the measurement carefully. If using a ruler, align one end of the pushrod with the zero mark and note where the opposite end aligns on the ruler. Record the measurement in writing, including the decimal places.

Repeat this process for all pushrods in the engine. In a typical small-block Chevrolet engine with eight cylinders, you'll have eight pushrods to measure. Document which pushrod came from which cylinder position. If all pushrods measure the same, your engine is using a single pushrod length. If measurements vary, different cylinders may have different-length pushrods due to previous modifications or manufacturing variations.

Examine the physical condition of your pushrods as you remove them. Look for bending, scoring, or wear on the ball ends (the rounded ends that contact the rocker arm and lifter). Damaged pushrods should be replaced, even if their length is correct. A bent pushrod cannot be accurately measured and will cause valve train problems.

Practical Takeaway: Keep all eight pushrods from your engine organized and labeled (intake side versus exhaust side, cylinder numbers) so you can reference measurements for replacement ordering. If you're keeping original pushrods, photograph them in place before removal to document their positions.

The Pushrod Length Calculation Method

If you're building an engine from scratch or replacing pushrods in a significantly modified engine, you may need to calculate the correct pushrod length rather than simply matching existing pieces. This calculation accounts for variations in block deck height, head casting thickness, lifter type, rocker arm style, and stud or bolt positioning. While engine machine shops typically handle complex calculations for heavily modified engines, understanding the basic method helps you follow the process and verify results.

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The fundamental principle involves measuring the distance from the pushrod seat location on the lifter to the pushrod hole location in the rocker arm. This distance, combined with accounting for the contact points where the pushrod ball ends meet these components, determines the required pushrod length. To perform this measurement, you must have the cylinder block with installed lifters and the cylinder head positioned exactly as they would be during normal engine assembly, with proper gasket thickness between them.

Begin by measuring from the top of the lifter (where the pushrod's ball end contacts it) to the rocker arm pivot point (often called the rocker arm stud). Measure straight up in a vertical line. Next, measure from the rocker arm pivot point to the center of the valve stem (where the rocker arm's opposite end contacts the valve). Add these two measurements together. The result should closely match your engine's specified pushrod length.

Different lifter types—solid lifters versus hydraulic lifters—sometimes affect this calculation because they have different heights. Similarly, different rocker arm styles (stamped steel versus forged aluminum, different pivot designs) may require slight adjustments. This is why precision measurement and documentation matter: variations of even 0.050 inch can affect valve lash and engine performance.

Many engine builders use a different practical method: the trial-and-error approach using adjustable pushrods or pushrod length gauges. These tools allow you to temporarily install a pushrod of adjustable length while