Komatsu PC50 Track Adjuster Reseal Procedure and Wear Diagnosis

[MikePhua]

The PC50 and Komatsu’s Compact Excavator Lineage
The Komatsu PC50 is part of Komatsu’s compact excavator family, designed for urban construction, landscaping, and utility trenching. With an operating weight around 5 metric tons and a hydraulic system tuned for precision and responsiveness, the PC50 blends power with maneuverability. Its undercarriage features a conventional track tensioning system using a grease-filled hydraulic adjuster, which maintains proper track sag and prevents derailment during operation.
Komatsu, founded in 1921 in Japan, has become one of the world’s leading manufacturers of construction and mining equipment. The PC series has sold in the tens of thousands globally, with the PC50 earning a reputation for reliability in tight quarters and challenging terrain.
Terminology Annotation:

• Track Adjuster: A hydraulic mechanism that maintains proper tension in the excavator’s track chain.
  
• Grease-Filled Adjuster: A piston assembly pressurized by grease to extend and retract the idler position.
  
• Track Sag: The vertical distance between the track and the top of the carrier roller, used to measure tension.
  

Symptoms of Adjuster Seal Failure
When the track adjuster begins to leak or lose pressure, operators may notice:

• Excessive track sag or slack
  
• Grease leaking from the adjuster housing
  
• Idler retracting during operation
  
• Difficulty maintaining alignment on slopes
  
• Visible contamination around the seal area
  

In one trenching job in Queensland, a PC50 began derailing during turns. Inspection revealed a failed adjuster seal that allowed grease to escape and the idler to retract under load. After resealing the adjuster and refilling the grease chamber, the issue was resolved.
Disassembly and Inspection Procedure
Resealing the track adjuster requires careful disassembly and cleaning. Steps include:

• Safely lifting the machine and relieving track tension by removing grease from the adjuster fitting
  
• Removing the track chain from the idler to expose the adjuster assembly
  
• Unbolting the adjuster cylinder from the frame
  
• Extracting the piston and inspecting for scoring, pitting, or rust
  
• Cleaning the bore and replacing seals, wipers, and O-rings
  

Recommendations:

• Use OEM seal kits matched to the adjuster model
  
• Inspect the piston rod for straightness and surface finish
  
• Replace any damaged bushings or wear rings
  
• Lubricate seals with compatible grease before reassembly
  

Terminology Annotation:

• Piston Rod: The shaft that moves within the adjuster cylinder to push the idler forward.
  
• Wiper Seal: A seal that prevents dirt and debris from entering the cylinder during extension.
  
• Wear Ring: A sacrificial component that prevents metal-to-metal contact between piston and bore.
  

In one municipal fleet in Michigan, a technician found that the piston rod had developed a slight bend from repeated impacts. After machining the rod and installing new seals, the adjuster held pressure and restored track alignment.
Grease Refill and Tensioning Strategy
After resealing, the adjuster must be refilled and tensioned properly:

• Inject grease through the fill fitting using a high-pressure gun
  
• Monitor idler movement until correct sag is achieved (typically 1–2 inches)
  
• Cycle the track forward and backward to settle the chain
  
• Recheck sag and adjust as needed
  

Tips:

• Use lithium-based grease rated for high pressure
  
• Avoid over-tensioning, which can accelerate undercarriage wear
  
• Check for leaks around the seal area during refill
  
• Document tension settings for future reference
  

Terminology Annotation:

• Fill Fitting: A threaded port used to inject grease into the adjuster chamber.
  
• Lithium-Based Grease: A common multipurpose grease with good water resistance and pressure tolerance.
  
• Undercarriage Wear: Degradation of track components due to friction, misalignment, or over-tensioning.
  

In one excavation firm in Nevada, switching to a synthetic grease with higher temperature tolerance reduced seal failures during summer operations.
Preventative Maintenance and Inspection Intervals
To extend adjuster life and prevent seal failure:

• Inspect track sag weekly and adjust as needed
  
• Clean grease fittings monthly to prevent contamination
  
• Replace seals every 2,000 hours or during undercarriage overhaul
  
• Monitor for unusual track noise or derailment tendencies
  

In one forestry loader in Oregon, implementing a quarterly undercarriage inspection program reduced adjuster failures by 70% and extended track life by 30%.
Conclusion
Resealing the track adjuster on a Komatsu PC50 is a practical repair that restores tension integrity and prevents derailment. With proper disassembly, seal replacement, and grease management, the adjuster can perform reliably across thousands of operating hours. In compact excavators, track tension is more than a setting—it’s a safeguard against downtime, wear, and misalignment. When the adjuster holds, the machine moves with confidence.