Hitachi EX120 Turntable and Ball Bearing Replacement: A Comprehensive Guide

[MikePhua]

When it comes to maintaining and repairing construction machinery, the components that see the most wear and tear are often those that endure constant movement, pressure, and friction. One such component is the turntable and its ball bearings, a crucial part of tracked excavators like the Hitachi EX120. Over time, these parts can suffer from wear, causing issues such as excessive noise, decreased maneuverability, and even mechanical failure. This guide will dive into the process of replacing the turntable and ball bearings on the Hitachi EX120, offering a detailed, step-by-step approach to ensure optimal performance and reliability.
Understanding the Turntable and Ball Bearings
Before delving into the replacement process, it’s important to understand the role these components play in the overall operation of the excavator.
The turntable is the rotating platform that supports the upper structure of the excavator, including the cab, arm, and bucket. It allows for 360-degree rotation, enabling the excavator to perform a wide range of tasks without having to reposition the entire vehicle. This movement is powered by the hydraulic system, which drives the gears connected to the turntable.
Ball bearings, on the other hand, reduce friction between the turntable and the undercarriage, enabling smooth rotation. These bearings are designed to withstand both radial and axial loads, but over time, they can degrade due to exposure to dirt, debris, and the sheer forces generated during operation.
Signs That Turntable Bearings Need Replacement
There are several signs that indicate the turntable bearings on your Hitachi EX120 may need to be replaced. These include:

1. Excessive Noise – A grinding or squeaking noise coming from the turntable area is often the first sign that the bearings are worn.
   
2. Jerky Rotation – If the turntable’s rotation becomes uneven or jerky, it may indicate that the bearings are damaged or failing.
   
3. Increased Play – Any noticeable movement or play in the turntable when it’s supposed to be stationary suggests bearing wear.
   
4. Leaks – Hydraulic fluid leaks from the turntable assembly can also point to bearing or seal failure, as they often work together to keep the system sealed and functioning properly.
   

Step-by-Step Guide to Replacing the Turntable and Ball Bearings
Replacing the turntable and ball bearings is a complex process that requires patience, attention to detail, and the right tools. Below is a step-by-step guide to help you through the process:
1. Preparing for the Job
Before starting the replacement, ensure you have the following tools and equipment:

• Hydraulic jack and support stands
  
• Socket set and wrenches
  
• Torque wrench
  
• Pry bars
  
• New turntable ball bearings
  
• New seals (if required)
  
• Grease for lubrication
  
• Safety gloves and goggles
  

Once you have all the tools ready, park the excavator on a flat surface and ensure the engine is turned off and the hydraulic pressure is relieved. Safety should always be the first priority, so make sure to wear the necessary protective equipment.
2. Lifting the Excavator
Using the hydraulic jack, lift the excavator slightly off the ground to allow for easy access to the turntable assembly. Ensure the excavator is securely supported using jack stands to prevent any accidents during the repair.
3. Removing the Turntable
The next step is to remove the turntable. Depending on your specific model, the turntable may be secured with a series of bolts or fasteners. Use your socket set and wrenches to remove these bolts carefully. It’s important to keep track of the bolts and their locations for reassembly. Once all bolts are removed, you may need to use a pry bar to gently lift the turntable off the undercarriage.
4. Inspecting the Ball Bearings and Turntable
With the turntable removed, inspect the ball bearings for signs of wear. Look for any visible cracks, discoloration, or missing balls, all of which are signs that the bearings need to be replaced. You should also check the raceways for any grooves or scoring. If the bearings show significant signs of wear, it’s best to replace them entirely.
Inspect the turntable for any damage or excessive wear as well. If the turntable surface is damaged, it may need to be resurfaced or replaced.
5. Installing New Bearings
Before installing the new ball bearings, clean the bearing seats on both the turntable and the undercarriage thoroughly. Any dirt or debris can cause premature wear or improper seating. Apply a thin layer of grease to the bearing seats to ensure smooth installation.
Place the new ball bearings carefully into their designated spots. It’s essential to ensure that the bearings are seated correctly to prevent uneven wear or damage.
6. Reassembling the Turntable
Once the new bearings are in place, carefully lower the turntable back into position on the undercarriage. Align the bolt holes and reinstall the bolts that hold the turntable in place. It’s crucial to tighten these bolts in a cross-pattern to ensure even pressure distribution. Use a torque wrench to tighten the bolts to the manufacturer’s specifications.
7. Testing the Excavator
Once everything is reassembled, perform a thorough check to ensure everything is secure. Start the excavator and test the turntable’s movement. Listen for any unusual noises and check for smooth, even rotation. If the movement is jerky or the bearings are still noisy, you may need to disassemble the turntable again and inspect the installation.
8. Final Adjustments
If necessary, make any final adjustments to the turntable assembly. This could involve checking the tightness of the bolts, ensuring that the hydraulic lines are properly connected, and checking for any leaks.
The Importance of Regular Maintenance
Replacing the turntable and ball bearings on your Hitachi EX120 is a critical maintenance task that can greatly extend the life of your machine. Regular inspections and prompt replacement of worn parts can prevent costly repairs and keep your excavator running smoothly.
It’s also important to lubricate the turntable bearings regularly to reduce friction and wear. In particularly dusty or muddy environments, consider using high-quality seals and greases to protect the bearings from contaminants.
Conclusion
The turntable and ball bearings on the Hitachi EX120 are essential components for ensuring the smooth operation of the excavator. By following the steps outlined above and performing regular maintenance, you can keep your machine in top working condition, avoiding costly downtime and repairs. Remember that proper care and attention to detail will not only improve performance but also enhance the longevity of your equipment.