Hitachi EX120-5 Excavator: Common Issues and Troubleshooting

[MikePhua]

The Hitachi EX120-5 excavator, a mid-sized machine introduced in the late 1990s, has been a reliable workhorse for various construction and excavation projects. However, like any piece of heavy machinery, it is susceptible to certain issues that can affect its performance. Understanding these common problems and their solutions can help operators and technicians maintain the machine's efficiency and longevity.
Hydraulic System Issues
One of the most frequently reported problems with the EX120-5 involves the hydraulic system. Operators have noted instances where the machine exhibits jittery movements or reduced power, particularly when the hydraulic system is under load. This can often be attributed to several factors:

• Air in the Hydraulic System: Air pockets can form in the hydraulic lines, leading to erratic movements and a loss of power. Bleeding the system to remove trapped air can resolve this issue.
  
• Contaminated Hydraulic Fluid: Dirt or debris in the hydraulic fluid can cause blockages and wear on components. Regularly changing the hydraulic fluid and replacing filters can prevent this problem.
  
• Worn Hydraulic Pump Seals: Over time, seals can degrade, leading to leaks and reduced pressure. Inspecting and replacing worn seals can restore proper function.
  
• Clogged Filters: Filters that are blocked can impede fluid flow, causing system inefficiencies. Ensuring filters are clean and replaced as needed is crucial.
  

Electrical System Challenges
Electrical issues can also affect the EX120-5's performance. One common symptom is the engine starting at full throttle and not idling correctly. This may be due to:

• Throttle Control Calibration: The throttle control system may require recalibration. Performing a "learn" procedure can help the system recognize the correct idle settings.
  
• Faulty Ignition Switch: A malfunctioning ignition switch can cause erratic engine behavior. Replacing the switch can resolve this issue.
  
• Wiring Issues: Loose or corroded connections can lead to inconsistent electrical signals. Inspecting and repairing wiring connections can improve performance.
  

Cooling System Overheating
Overheating is another concern, especially when the air conditioning is in use. Possible causes include:

• Clogged Radiator: Debris can accumulate in the radiator, reducing airflow and cooling efficiency. Cleaning the radiator can alleviate this problem.
  
• Inadequate Hydraulic Oil: Using non-recommended hydraulic oils can lead to overheating. It's essential to use the manufacturer's specified oil to maintain optimal temperature levels.
  

Travel Motor Performance
Uneven travel motor performance, such as one side moving slower than the other, can be caused by:

• Internal Motor Wear: Worn components within the travel motor can reduce efficiency. Inspecting and replacing worn parts can restore balance.
  
• Valve Spool Issues: Contaminated or sticking valve spools can affect motor performance. Cleaning or replacing the valve spools can resolve this issue.
  

Maintenance Recommendations
To prevent these issues and ensure the longevity of the Hitachi EX120-5 excavator:

• Regular Inspections: Conduct thorough checks of hydraulic, electrical, and cooling systems.
  
• Timely Replacements: Replace filters, seals, and fluids as per the manufacturer's maintenance schedule.
  
• Use Recommended Parts: Always use parts and fluids specified by Hitachi to maintain compatibility and performance.
  
• Professional Servicing: Engage qualified technicians for complex repairs and calibrations.
  

By addressing these common issues proactively, operators can ensure that their Hitachi EX120-5 excavator continues to perform efficiently and reliably on the job site.