Troubleshooting a Hitachi 120-2 Excavator That Won’t Swing

[MikePhua]

Introduction: Common Problems with Excavators and the Importance of Swing Mechanisms
Excavators, such as the Hitachi 120-2, are essential machines in construction and excavation projects. One of the most important functions of an excavator is its ability to swing the upper structure, or the house, relative to the undercarriage. This movement is crucial for digging, lifting, and positioning materials. A problem with the swing mechanism can severely hinder the performance of an excavator, and one of the more common issues faced by operators is when the machine won’t swing.
If your Hitachi 120-2 excavator is failing to swing, it’s essential to troubleshoot the issue quickly to minimize downtime. In this article, we’ll walk through the common causes of a non-functioning swing mechanism and provide actionable solutions.
Understanding the Swing Mechanism and Its Importance
The swing mechanism in an excavator allows the upper part of the machine (the house) to rotate around the base. This movement is powered by a hydraulic motor and gear system. The swing mechanism is critical for a range of tasks, including:

• Digging along a trench or pit without needing to reposition the machine.
  
• Lifting and placing materials with precision.
  
• Performing tasks that require continuous rotation, such as loading trucks or positioning attachments.
  

When the swing stops working, it significantly affects the machine's efficiency, leading to delays and increased operational costs. Therefore, understanding the root causes of a failed swing is crucial for maintaining the machine’s productivity.
Common Causes of Swing Failure in Hitachi 120-2 Excavators

1. Low Hydraulic Fluid Levels
   One of the first things to check when the swing isn’t working is the hydraulic fluid level. Hydraulic fluid is the lifeblood of the swing system, providing the necessary pressure to power the swing motor. If the fluid level is low due to leaks or insufficient maintenance, the swing mechanism may stop working.
   • How to Check: The hydraulic fluid level should be checked regularly, as part of the excavator’s overall maintenance schedule. Low levels can be topped up with the appropriate type of hydraulic fluid, which should be specified in the operator’s manual.
     
   • Leaks: If the fluid is low, inspect the hydraulic hoses and connections around the swing motor and pump. Look for signs of leaks, which could lead to loss of hydraulic pressure. If any leaks are found, they should be repaired immediately.
     
2. Faulty Swing Motor
   The swing motor is responsible for powering the rotation of the excavator’s upper house. If the swing motor fails or becomes damaged, it can prevent the swing from functioning.
   • Symptoms of a Faulty Motor: If the motor is malfunctioning, you might notice unusual noises, such as grinding or whining sounds, coming from the swing area. Additionally, you may experience intermittent swinging or a complete failure to rotate the upper structure.
     
   • What to Do: If you suspect the motor is faulty, the motor should be tested and, if necessary, replaced or repaired by a professional technician. It’s critical to use the correct replacement parts specified for your machine to ensure optimal performance.
     
3. Swing Hydraulic Valve Issues
   The swing hydraulic valve controls the flow of fluid to the swing motor. If the valve becomes blocked or malfunctioning, it can prevent the swing from working properly. The valve may also be affected by dirt, debris, or internal wear.
   • Signs of Valve Problems: If the valve is malfunctioning, you may notice erratic swinging or no movement at all. In some cases, the swing may start and stop intermittently.
     
   • Solution: Inspect the valve for blockages or damage. If debris is found, the valve should be cleaned thoroughly. If the valve is worn out or damaged, it may need to be replaced to restore the swing function.
     
4. Faulty Swing Gearbox or Swing Bearing
   The swing mechanism also includes a gearbox and bearing system that supports the rotation of the upper house. Over time, the gearbox or bearings may wear out, leading to issues with the swing function.
   • Symptoms: If the gearbox or bearings are worn, you may notice abnormal sounds, such as clicking or grinding, during swinging. In some cases, the upper house may feel loose or wobble when attempting to swing.
     
   • What to Do: If you suspect an issue with the swing gearbox or bearings, it’s important to inspect the components thoroughly. If wear or damage is found, these parts should be replaced. Regular lubrication of the bearings can help reduce wear and extend their lifespan.
     
5. Electrical or Sensor Problems
   Modern excavators, like the Hitachi 120-2, are equipped with sensors and electrical systems that control various functions, including the swing. A malfunctioning sensor or electrical connection can lead to swing failure.
   • Signs of Electrical Issues: If the excavator’s electrical system is at fault, you may see warning lights on the dashboard or experience erratic behavior in the swing function. The swing may not respond at all or may behave unpredictably.
     
   • Solution: Check the electrical connections related to the swing motor and sensors. Inspect for loose connections, corrosion, or damaged wires. If the problem persists, a diagnostic scan of the machine’s electronic system can help identify faulty sensors or wiring issues.
     

How to Troubleshoot and Fix the Swing Mechanism

1. Check Fluid Levels:
   Start by inspecting the hydraulic fluid levels. Top up the fluid if necessary and check for leaks. Ensuring that the hydraulic system is properly filled and sealed is often the easiest and quickest fix for swing-related issues.
   
2. Inspect the Swing Motor:
   If the fluid levels are correct and the swing still doesn’t work, examine the swing motor for signs of failure. This may require removing panels and visually inspecting the motor for leaks or wear. If the motor is damaged, it may need to be rebuilt or replaced.
   
3. Test the Swing Valve:
   Check the hydraulic valve for any blockages or damage. If the valve is clogged, clean it and ensure there is no debris obstructing the fluid flow. If the valve is defective, it will need to be replaced.
   
4. Examine the Gearbox and Bearings:
   Listen for abnormal sounds from the gearbox or bearings. If any damage or excessive wear is noticed, these components should be replaced to restore proper swing function.
   
5. Check Electrical and Sensor Systems:
   If none of the mechanical or hydraulic issues seem to be the cause, turn to the electrical system. Inspect sensors and wiring connected to the swing motor. A diagnostic tool can help pinpoint electrical issues that may be affecting the swing function.
   

Real-World Example: Common Issue on a Construction Site
In a real-world scenario, a construction company in Nevada experienced a non-functioning swing on their Hitachi 120-2 excavator. After performing basic checks on fluid levels and finding no obvious issues, the technician discovered that a clogged swing valve was the culprit. After clearing the valve, the excavator’s swing returned to full functionality, allowing the crew to resume operations without significant delays.
This example highlights the importance of a thorough troubleshooting process. By addressing even the smallest issue, such as a blocked valve, operators can often restore function without resorting to expensive repairs.
Conclusion: Keeping Your Hitachi 120-2 in Optimal Condition
A non-functioning swing mechanism on your Hitachi 120-2 excavator can be caused by a variety of issues, including low hydraulic fluid, a faulty swing motor, hydraulic valve problems, worn gearbox or bearings, or electrical system malfunctions. Regular maintenance, including fluid checks, lubrication, and sensor inspections, is essential for keeping the swing mechanism operating smoothly.
By systematically troubleshooting the issue and addressing the root cause, you can quickly restore the swing function and keep your machine running efficiently. If the problem persists despite these checks, consulting a professional technician is advisable to ensure long-term reliability and minimize downtime.