Resolving Stiff Track Lever Movement on the Komatsu PC20-6

[MikePhua]

The PC20-6 and Its Compact Excavator Heritage
The Komatsu PC20-6 is a compact hydraulic excavator introduced in the late 1980s, designed for urban trenching, landscaping, and utility work. With an operating weight around 2,000 kg and powered by a Komatsu 3D82E diesel engine producing approximately 22 horsepower, the PC20-6 was part of Komatsu’s push into the mini-excavator market. Its mechanical simplicity, narrow footprint, and responsive controls made it a favorite among small contractors and rental fleets.
Komatsu, founded in 1921, has built a reputation for durable earthmoving equipment. The PC-series excavators have sold in the tens of thousands globally, with the PC20-6 remaining in service across Asia, Europe, and North America. Despite its age, the machine’s mechanical control system allows for field repairs without complex electronics—though wear and stiffness in control linkages can emerge over time.
Track Lever Function and Hydraulic Control
The PC20-6 uses dual travel levers to control the left and right tracks independently. These levers are mechanically linked to pilot valves that direct hydraulic flow to the travel motors. When the operator pushes a lever forward or backward, the corresponding valve opens, allowing pressurized fluid to drive the track in the desired direction.
Key components include:

• Mechanical linkage rods and pivot joints
  
• Pilot control valves mounted beneath the operator platform
  
• Return springs and detents for neutral positioning
  
• Hydraulic hoses and fittings leading to travel motors
  

Smooth lever movement is essential for precise tracking, turning, and maneuvering in confined spaces. Stiffness or resistance in one lever—typically the right-hand side—can indicate mechanical binding, contamination, or internal valve wear.
Common Causes of Lever Stiffness
Stiff movement in the right-hand track lever may result from:

• Corroded or dry pivot joints in the linkage assembly
  
• Bent or misaligned control rods
  
• Debris or rust buildup around the valve housing
  
• Worn bushings or seized bearings
  
• Internal contamination in the pilot valve
  
• Hydraulic fluid degradation or air entrapment
  

A technician in Osaka reported that a PC20-6 in his fleet developed stiffness in the right lever after prolonged storage in a humid yard. Upon inspection, the pivot shaft had seized due to rust, and the linkage rod was slightly bent from a previous impact.
Inspection and Diagnosis Strategy
To isolate the problem:

• Remove the operator platform to expose the linkage assembly
  
• Inspect all pivot points for free movement and lubrication
  
• Check for rod alignment and signs of bending or abrasion
  
• Disconnect the linkage from the valve and test lever movement independently
  
• Inspect the pilot valve for internal resistance or contamination
  
• Verify hydraulic fluid level and condition
  

If the lever moves freely when disconnected from the valve, the issue lies within the valve body or hydraulic circuit. If stiffness remains, mechanical binding is the likely cause.
Repair and Lubrication Procedure
For mechanical linkage issues:

• Clean all pivot joints with solvent and compressed air
  
• Apply high-pressure grease to bushings and shafts
  
• Replace worn bearings or nylon washers
  
• Realign bent rods using a press or replace if deformed
  
• Install new return springs if tension is uneven
  

For pilot valve issues:

• Remove valve and disassemble carefully
  
• Inspect spool and bore for scoring or debris
  
• Clean with lint-free cloth and hydraulic-safe solvent
  
• Replace O-rings and seals with OEM-grade components
  
• Reassemble and torque to spec
  

Use ISO 46 hydraulic fluid or Komatsu-approved equivalent. Bleed air from the system after reassembly to ensure smooth operation.
Preventive Measures and Long-Term Care
To prevent future stiffness:

• Lubricate control linkages every 250 hours
  
• Store machine under cover to reduce moisture exposure
  
• Inspect valve seals annually
  
• Flush hydraulic fluid every 1,000 hours or biannually
  
• Avoid excessive force on levers during operation
  

Operators should report any change in lever feel immediately. Early intervention prevents wear from escalating into valve damage or control failure.
Conclusion
Stiff movement in the right-hand track lever of a Komatsu PC20-6 is typically caused by mechanical binding or pilot valve contamination. With proper inspection, lubrication, and part replacement, the issue can be resolved without extensive downtime. These compact excavators, though aging, remain reliable workhorses when maintained with care—proving that mechanical simplicity still has a place in modern job sites.