Excavators rely on powerful diesel engines to generate the immense force required for heavy-duty earthmoving tasks. Within these engines, push rods play a crucial role in the valve train system, ensuring precise control over intake and exhaust valve operation. Though small in size, these components are fundamental to an engine’s performance, reliability, and longevity.
In this blog, we will explore:
What push rods are and their role in an excavator engine
How they function in the valve train system
The materials used in push rod construction
Common failures and signs of wear
Best practices for maintenance and replacement
What Are Push Rods?
Push rods are slender cylindrical rods that form part of the overhead valve (OHV) system in many diesel-powered excavator engines. They connect the camshaft to the rocker arms, which in turn open and close the engine’s valves.
Push rods function as mechanical linkages, transmitting motion from the camshaft lobes to the valves via the rocker arms. Since diesel excavators often use high-compression engines with strong valve springs, push rods must be highly durable and precisely engineered to withstand the extreme forces within the engine.
The Role of Push Rods in an Excavator Engine
Excavator engines operate using the four-stroke combustion cycle:
Intake Stroke – The intake valve opens, allowing air and fuel to enter the combustion chamber.
Compression Stroke – The intake and exhaust valves close as the piston moves upward, compressing the air-fuel mixture.
Power Stroke – The fuel ignites, creating an explosion that forces the piston downward.
Exhaust Stroke – The exhaust valve opens, allowing burnt gases to escape before the cycle repeats.
Push rods contribute directly to this process by precisely timing valve actuation. Here’s how:
The camshaft rotates, and its lobes push against the lifter (tappet) at the bottom of the push rod.
The push rod transfers this movement upward to the rocker arm.
The rocker arm pivots and pushes the valve downward, opening it.
When the camshaft lobe moves away, the valve spring forces the valve back up, and the push rod returns to its original position.
This synchronized motion ensures efficient air-fuel intake and exhaust gas expulsion, directly affecting engine power, efficiency, and emissions.
Materials and Construction of Push Rods
Since push rods operate under high loads, pressure, and extreme temperatures, manufacturers use materials that provide superior strength, durability, and heat resistance. The most common materials include:
Hardened steel – Offers high tensile strength and wear resistance.
Chromoly steel (Chromium-Molybdenum alloy) – Used in heavy-duty applications for its superior toughness.
Aluminum – Lightweight, but typically used in performance applications rather than in heavy-duty excavators.
Many push rods also feature hollow-core designs to reduce weight while maintaining strength, and some are filled with oil for additional lubrication.
Common Push Rod Failures and Signs of Wear
Push rods are subjected to constant mechanical stress, and over time, they may experience wear or failure. Here are the most common issues:
1. Bent Push Rods
Caused by excessive valve spring pressure, misaligned components, or hydraulic lock due to fuel or coolant entering the combustion chamber.
Symptoms: Ticking noises, loss of power, misfires, or difficulty starting the engine.
2. Worn or Broken Push Rods
Continuous operation in high-load environments may cause wear at the ends where they contact the lifter and rocker arm.
Symptoms: Inconsistent valve movement, knocking sounds, or a loss of engine efficiency.
3. Lifter and Rocker Arm Damage
If a push rod bends or breaks, it can damage the lifter, rocker arm, or even the camshaft.
Symptoms: Excessive valve lash (clearance), rough idling, or engine hesitation.
4. Insufficient Lubrication
Push rods rely on engine oil to reduce friction. Poor lubrication leads to premature wear.
Symptoms: Metal shavings in oil, excessive heat, and noisy operation.
Preventative Maintenance and Best Practices
To extend the life of push rods and prevent costly engine damage, follow these best practices:
1. Regular Valve Adjustments
Diesel engines often require periodic valve lash adjustments to maintain proper clearance.
Improper clearance can cause excessive stress on push rods, leading to premature wear or failure.
2. Use High-Quality Engine Oil
Proper lubrication is critical for push rod longevity. Always use the manufacturer-recommended oil grade.
Change oil and filters at scheduled intervals to prevent contaminants from accelerating wear.
3. Inspect Push Rods During Overhauls
Whenever performing major engine maintenance, remove and inspect push rods for straightness and wear.
If a push rod is bent, cracked, or excessively worn, replace it immediately.
4. Ensure Proper Torque on Fasteners
Rocker arm fasteners must be torqued correctly to avoid uneven push rod movement and premature failure.
5. Monitor Engine Performance
Keep an eye on engine power, fuel efficiency, and unusual noises.
Early detection of ticking or knocking sounds can help prevent a small issue from turning into a major repair.
Replacing a Faulty Push Rod
If an excavator engine experiences push rod failure, follow these steps for safe replacement:
Shut down the engine and allow it to cool.
Remove the valve cover to access the rocker arms and push rods.
Inspect all push rods for straightness and wear. If any are bent or damaged, replace them.
Lubricate the new push rods with engine oil before installation.
Reinstall the rocker arms and adjust valve clearance according to OEM specifications.
Start the engine and check for smooth operation.
Why High-Quality Replacement Push Rods Matter
Not all replacement push rods are created equal. Choosing OEM or high-quality aftermarket parts ensures:
Correct dimensions and material composition
Superior heat and wear resistance
Reliable performance under high loads
For businesses operating excavators, downtime is costly. Investing in quality used OEM push rods from a trusted supplier like Vikfin ensures reliability without the high cost of new parts.
Conclusion
Push rods are an essential part of an excavator engine’s valve train system, enabling smooth and efficient operation. Despite their simple appearance, they play a critical role in engine timing, fuel efficiency, and overall performance.
Regular maintenance, proper lubrication, and early detection of wear can prevent costly failures and extend the life of an engine. For those looking to replace push rods, opting for high-quality used OEM components is a cost-effective and reliable solution.
If you're in need of excavator push rods or other high-quality used OEM parts, Vikfin has you covered—offering durable, tested components at market-beating prices to keep your machines running with minimal downtime.
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