Hitachi EX120 Swing Bearing Bolt Maintenance

[MikePhua]

The Hitachi EX120 is a powerful and widely used model of hydraulic excavators. It’s known for its reliability, performance, and ability to handle various tasks, from digging to lifting and earthmoving. One crucial component that ensures the efficient operation of the EX120 is its swing bearing, which allows the upper structure of the excavator to rotate. However, over time, like all mechanical parts, the swing bearing bolts can experience wear and tear. Ensuring the swing bearing bolts are in good condition and properly maintained is essential for preventing costly repairs and extending the machine's life. This article explores the significance of the swing bearing bolts, common issues associated with them, and tips for maintaining and replacing them when necessary.
What is the Swing Bearing on the Hitachi EX120?
The swing bearing, also known as the slew ring or turntable bearing, is a critical component of any tracked excavator, including the Hitachi EX120. It allows the upper portion of the excavator, including the cab, arm, and bucket, to rotate smoothly around the base. The swing bearing is composed of several elements: the raceway, the gear teeth, and the rolling elements (such as steel balls or rollers).
As the excavator operates, the swing bearing experiences constant rotational forces and heavy loads, especially when lifting or swinging the boom under load. These stresses can lead to wear, which, if not addressed, can cause the swing bearing to fail, resulting in costly downtime and repairs.
Swing Bearing Bolts and Their Importance
The swing bearing is held in place by a set of bolts that secure it to the machine’s undercarriage. These bolts play a critical role in ensuring the stability and integrity of the swing bearing. Over time, due to continuous motion, vibration, and load-bearing stress, these bolts can become loose or damaged. If left unchecked, the loose or damaged bolts can lead to excessive wear on the swing bearing, improper alignment, and even catastrophic failure of the bearing itself.
Regular inspection and proper torqueing of these bolts are essential for maintaining the performance and longevity of the swing bearing. Additionally, ensuring the bolts are in good condition can prevent more significant issues, such as frame or structural damage.
Common Problems with Swing Bearing Bolts

1. Loose Bolts
   One of the most common issues with the swing bearing bolts on the Hitachi EX120 is loosening. Due to the repetitive stress and vibration from the excavator’s movement, the bolts may gradually loosen over time. If not noticed early, this can result in excessive play in the swing bearing, leading to more serious damage and premature failure.
   
2. Bolt Damage and Wear
   The swing bearing bolts themselves can experience wear over time due to the constant forces applied to them. This can lead to cracked or worn bolts, which might not provide adequate holding strength. Over time, this can lead to improper operation of the swing bearing, making it harder to rotate the upper structure or causing irregular movements.
   
3. Corrosion
   Environmental factors, such as moisture, dirt, and chemicals, can lead to corrosion of the swing bearing bolts. Corrosion weakens the bolts, making them more susceptible to failure. In extreme cases, corroded bolts may snap, causing the swing bearing to detach or fail.
   
4. Improper Torqueing
   If the bolts are not torqued correctly during installation or maintenance, they may not perform optimally. Under-torqued bolts can loosen quickly, while over-torqued bolts can stress the threads, leading to early failure. Proper torque specifications should always be followed when working on the swing bearing.
   

How to Maintain and Inspect Swing Bearing Bolts

1. Regular Inspections
   Inspecting the swing bearing bolts regularly is crucial for detecting any issues early. This can include visual checks for signs of wear, cracking, or corrosion. Also, checking for any movement or play in the swing bearing during operation can be an indicator that the bolts are loose or damaged.
   
2. Tightening and Retorquing
   Periodically, it's necessary to check the torque of the swing bearing bolts and retorque them to the manufacturer’s specifications. This is particularly important after the machine has undergone heavy use or been subjected to rough working conditions. Ensure the bolts are tightened in a cross-pattern to achieve even distribution of stress.
   
3. Replacing Worn or Damaged Bolts
   If any bolts are found to be worn, cracked, or corroded, they should be replaced immediately. Continuing to use worn or damaged bolts could lead to further damage to the swing bearing and the machine’s frame. Always use OEM (Original Equipment Manufacturer) bolts for replacements, as these are designed specifically for the Hitachi EX120’s swing bearing.
   
4. Lubrication
   Keeping the swing bearing well-lubricated helps reduce friction and wear. Regularly lubricating the swing bearing can also help extend the life of the bolts by reducing the heat and stress caused by metal-to-metal contact. Check the lubricant level and quality regularly and replace it when necessary.
   
5. Addressing Corrosion
   If you notice signs of corrosion on the swing bearing bolts, it’s essential to address it as soon as possible. Clean the affected areas and apply corrosion-resistant coatings if needed. Regularly inspect the bolts for signs of corrosion and replace any bolts that have suffered significant damage.
   

When to Replace the Swing Bearing Bolts
There are several indicators that it may be time to replace the swing bearing bolts on your Hitachi EX120. These include:

• Visible damage or cracks on the bolts
  
• Loose bolts that cannot be retightened to the correct torque
  
• Excessive corrosion or rust
  
• Increased play or difficulty in rotating the upper structure of the excavator
  

If any of these issues are detected, it's crucial to stop using the machine until the bolts are replaced. Failure to address these issues can result in severe damage to the swing bearing, increased downtime, and costly repairs.
Conclusion
Maintaining the swing bearing bolts on your Hitachi EX120 is critical for ensuring the efficiency and longevity of your excavator. Regular inspection, proper torqueing, and replacing damaged bolts are key practices to prevent premature wear and prevent costly failures. While the swing bearing is built to withstand significant stress and load, the bolts that secure it are equally important. By staying on top of maintenance, you can extend the life of your machine, reduce downtime, and keep operations running smoothly.
Maintaining the swing bearing bolts not only protects the machine's functionality but also contributes to operator safety. Any issues with the swing bearing bolts should not be ignored, as they can lead to bigger and more costly repairs down the line. Keep your Hitachi EX120 in top condition by staying vigilant with its maintenance.