EX120 Swing Motor Intermittent Operation: Causes and Solutions

[MikePhua]

The EX120, a model of excavator from Hitachi, is known for its durability and versatility in various construction and mining applications. However, like all complex machinery, it can face operational issues. One such problem commonly reported by operators is the intermittent function of the swing motor. This issue can affect the performance of the machine, causing frustration and delays in operations. In this article, we will delve into the potential causes of intermittent swing motor issues on the EX120 and provide troubleshooting steps and solutions.
Overview of the Hitachi EX120 Excavator
The Hitachi EX120 is a compact and highly efficient excavator, known for its robust engine performance, advanced hydraulics, and precision control. This excavator is typically used for a wide range of earth-moving tasks, from digging and trenching to lifting and material handling. The EX120 is powered by a high-performance diesel engine that drives its hydraulics, including the swing motor, which is responsible for the rotational movement of the excavator's upper structure.
The swing motor is a vital component, providing the necessary power to rotate the excavator’s upper body (including the boom, bucket, and cabin) around the stationary undercarriage. If the swing motor operates intermittently, it can lead to inefficiencies, slow operation, and even potential damage to the system if not addressed promptly.
Common Causes of Intermittent Swing Motor Operation

1. Hydraulic Fluid Issues
   The swing motor relies on hydraulic power for its operation. If there are issues with the hydraulic fluid, such as low fluid levels, contamination, or improper fluid type, it can lead to intermittent performance. Insufficient fluid can cause the hydraulic pump to struggle, which results in irregular motor function. Contaminated fluid can clog filters or damage internal components, leading to inconsistent behavior.
   
2. Faulty Swing Motor Solenoid
   A malfunctioning solenoid is another common cause of intermittent swing motor operation. The solenoid controls the flow of hydraulic fluid to the swing motor. If the solenoid is faulty, it may fail to deliver the necessary fluid in a consistent manner, causing the motor to operate sporadically. Electrical issues such as poor connections or corrosion in the solenoid wiring can exacerbate this problem.
   
3. Damaged Swing Motor or Drive Gear
   Mechanical wear or damage to the swing motor itself or its associated drive gear can also result in intermittent operation. This issue is typically characterized by unusual noises, erratic movement, or complete failure to rotate the upper structure. Damage to internal gears or bearings within the motor can disrupt the rotation and reduce the efficiency of the swing operation.
   
4. Electrical and Sensor Problems
   The EX120’s swing motor is often controlled by a series of sensors that relay information about the motor’s performance to the machine’s control system. If there is a problem with these sensors, such as a malfunctioning speed sensor or rotational position sensor, it can cause the system to misinterpret the motor’s status, leading to intermittent performance. Wiring issues, faulty connections, or corrosion in the sensor system are common culprits.
   
5. Contamination of the Hydraulic System
   Contaminants like dirt, debris, or moisture can enter the hydraulic system, often through damaged seals or worn-out components. These contaminants can clog filters, block fluid flow, or damage the swing motor’s internal parts, causing it to operate inconsistently. This is a common issue in environments where the excavator is exposed to dust, mud, or other foreign substances.
   

Troubleshooting Intermittent Swing Motor Issues

1. Check Hydraulic Fluid Levels and Quality
   The first step in troubleshooting an intermittent swing motor is to check the hydraulic fluid levels and inspect its quality. Low fluid levels or dirty fluid should be replaced immediately. Ensure that the fluid meets the manufacturer’s specifications. Contaminated fluid can be flushed from the system, and the filters should be replaced to prevent further damage.
   
2. Inspect the Swing Motor Solenoid and Wiring
   If the hydraulic fluid appears to be in good condition, the next step is to inspect the solenoid that controls the hydraulic flow to the swing motor. The solenoid should be tested for proper operation using a multimeter. Additionally, check the wiring and connections for corrosion or loose connections, which can interfere with the solenoid’s performance. Any faulty components should be replaced.
   
3. Examine the Swing Motor and Drive Gear
   If the motor is still exhibiting intermittent behavior, the swing motor and drive gears should be inspected for signs of wear, damage, or lack of lubrication. This may involve removing the motor from the excavator to assess internal components like gears, bearings, and seals. A worn-out motor or gear system may require a full replacement or overhaul.
   
4. Test the Electrical Sensors
   Since the EX120 uses sensors to monitor and control the swing motor, it’s crucial to test these sensors for functionality. Use a diagnostic tool to check the performance of sensors like the swing speed sensor or position sensor. Any faulty sensors should be replaced, and the wiring should be inspected for any breaks or corrosion.
   
5. Check for Contaminants in the Hydraulic System
   If contaminants are suspected in the hydraulic system, it’s essential to conduct a thorough inspection of all seals, hoses, and fittings. Replace any damaged components and clean the system to prevent further contamination. A hydraulic flush may be necessary to remove dirt and debris from the lines and motor.
   

Preventative Measures for Swing Motor Maintenance
To avoid intermittent swing motor issues in the future, regular maintenance of the hydraulic system and swing motor is essential. Operators should follow these guidelines:

1. Routine Fluid Checks and Changes
   Perform regular checks on hydraulic fluid levels and quality. Change the fluid at the manufacturer’s recommended intervals to maintain optimal performance.
   
2. Clean the Hydraulic System
   Regularly clean and inspect the hydraulic system to prevent the buildup of contaminants. Replace filters at recommended intervals and check hoses and seals for leaks or damage.
   
3. Solenoid and Wiring Inspections
   Inspect the solenoids, sensors, and wiring for wear and tear regularly. Corroded or loose connections should be repaired immediately to ensure smooth operation of the swing motor.
   
4. Lubricate Moving Parts
   Ensure that all moving components, including the swing motor gears and bearings, are properly lubricated. This reduces wear and tear and prevents damage to the system.
   
5. Professional Inspections
   Schedule professional inspections of the hydraulic system and swing motor at regular intervals. This can help detect early signs of wear and allow for timely repairs, reducing the likelihood of major failures.
   

Conclusion
Intermittent operation of the swing motor on the Hitachi EX120 excavator can be caused by various factors, including hydraulic issues, faulty solenoids, mechanical damage, and electrical sensor problems. By following a methodical troubleshooting approach, operators can identify the root cause of the issue and implement the appropriate solution. Regular maintenance, including fluid checks, filter replacements, and sensor inspections, can help prevent these problems from arising and ensure the smooth and efficient operation of the excavator.