Push Rods

Push rods are key components in the valve train of an internal combustion engine, particularly in engines with an overhead valve (OHV) design. They play a crucial role in transmitting the motion from the camshaft to the rocker arms, which then actuate the valves. Here’s a detailed overview of push rods, their function, construction, and maintenance:

Function of Push Rods

1. Motion Transfer: Push rods transfer the rotational motion of the camshaft (located in the engine block) to the rocker arms (located in the cylinder head). As the camshaft rotates, it pushes against a lifter or tappet, which then moves the push rod. This movement is transmitted to the rocker arm, causing it to open and close the engine’s valves.

2. Valve Operation: By transmitting the camshaft’s motion to the rocker arms, push rods play a crucial role in controlling the timing and movement of the engine’s intake and exhaust valves. Proper operation ensures that the valves open and close at the correct times relative to the pistons' position.

Construction of Push Rods

1. Material: Push rods are typically made from strong, lightweight materials such as steel, aluminum, or composite materials. Steel push rods are common due to their strength and durability. In high-performance engines, lightweight materials like titanium or composite push rods may be used to reduce weight and improve performance.

2. Design: Push rods are usually cylindrical and hollow to reduce weight while maintaining strength. They have a uniform diameter and length to ensure proper fit and function within the engine.

3. Length and Diameter: The length and diameter of the push rod are critical for proper engine operation. They must match the specifications for the engine’s design to ensure correct valve timing and operation.

Types of Push Rod Mechanisms

1. Solid Push Rods: Made from a single piece of material, these push rods are durable and commonly used in many engine designs.

2. Hollow Push Rods: Designed with a hollow interior to reduce weight without compromising strength. These are often used in high-performance or racing engines.

Maintenance and Troubleshooting

1. Inspection: Regularly inspect push rods for signs of wear, bending, or damage. Look for surface imperfections, bending, or cracks that could affect performance.

2. Clearance Adjustment: Ensure proper valve lash (clearance) between the push rod and the rocker arm. Incorrect clearance can lead to poor engine performance, noise, or premature wear.

3. Lubrication: Ensure that the push rods are properly lubricated to reduce friction and wear. This is typically managed by the engine’s oiling system.

4. Replacement: Replace push rods if they are bent, damaged, or if engine performance issues arise. Damaged push rods can cause improper valve operation and lead to engine problems.

Common Issues

1. Bent Push Rods: Push rods can become bent due to excessive stress, incorrect valve timing, or other engine issues. Bent push rods can cause improper valve operation and engine performance problems.

2. Worn or Damaged Push Rods: Wear and tear can lead to surface damage or bending. Worn push rods can cause increased friction and improper valve movement.

3. Incorrect Valve Lash: Incorrect adjustment of valve lash can lead to improper push rod function, causing noise, poor performance, or excessive wear.

4. Push Rod Failure: In severe cases, push rods may break or fail due to excessive stress, poor lubrication, or manufacturing defects. This can lead to significant engine damage.

Conclusion

Push rods are essential components in an OHV engine’s valve train, transferring the camshaft’s motion to the rocker arms and ensuring proper valve operation. Regular inspection, proper maintenance, and timely replacement are crucial to ensuring that push rods continue to function effectively, maintaining optimal engine performance and reliability.