Diagnosing and Resolving Jerky Track Movement in the Kobelco SK120-5

[MikePhua]

Introduction
The Kobelco SK120-5, a mid-sized hydraulic crawler excavator, is renowned for its performance and reliability in various construction and excavation tasks. However, like any complex machinery, it can experience operational issues. One such issue reported by operators is jerky track movement, particularly noticeable after the machine has warmed up. This article delves into potential causes of this problem and offers insights into diagnosis and resolution.
Understanding the Problem
Operators have observed that one of the tracks on the SK120-5 exhibits jerky movement in one direction after the machine reaches operating temperature. This jerking is less pronounced when the control is eased forward but becomes more noticeable under normal operation. Interestingly, the issue often resolves temporarily when the control is abruptly engaged, suggesting a possible hydraulic or mechanical anomaly.
Potential Causes

1. Hydraulic System Contamination
   Contaminants such as dirt, debris, or degraded hydraulic fluid can obstruct the flow of hydraulic oil, leading to erratic movement of the track. The absence of visible oil leaks does not rule out internal contamination.
   
2. Final Drive Motor Issues
   The final drive motor, responsible for transmitting power to the tracks, can develop faults over time. Symptoms of a failing final drive include unusual noises, reduced power, and jerky movements.
   
3. Control Valve Malfunctions
   The travel control valve regulates the flow of hydraulic fluid to the track motors. A malfunctioning valve can cause uneven distribution of power, resulting in jerky track movement.
   
4. Undercarriage Wear
   Excessive wear in components such as sprockets, rollers, or track links can increase friction, leading to jerky movements. Regular inspection of the undercarriage is essential to identify and address such issues.
   

Diagnostic Steps
To accurately diagnose the cause of jerky track movement, consider the following steps:

• Inspect Hydraulic Fluid Quality: Check the hydraulic fluid for signs of contamination or degradation. Replace the fluid if necessary and ensure the system is properly filtered.
  
• Examine Final Drive Motor: Listen for unusual noises when the track is operated off the ground. Any abnormal sounds may indicate internal damage or wear.
  
• Test Control Valve Operation: Operate the travel controls and observe the response. Irregular movements or delayed reactions can point to valve issues.
  
• Assess Undercarriage Condition: Inspect the undercarriage for signs of wear or damage. Pay close attention to sprockets, rollers, and track links for any irregularities.
  

Conclusion
Jerky track movement in the Kobelco SK120-5 can stem from various hydraulic or mechanical issues. By systematically diagnosing potential causes and addressing them promptly, operators can restore the machine's performance and prevent further complications. Regular maintenance and vigilant monitoring are key to ensuring the longevity and reliability of the SK120-5.