Komatsu PC75 Undercarriage Rollers Inspection and Replacement Guide

[MikePhua]

The PC75 and Komatsu’s Compact Excavator Lineage
The Komatsu PC75 is a mid-sized compact excavator designed for urban construction, utility trenching, and light demolition. Introduced as part of Komatsu’s PC series, the PC75 blends the maneuverability of a mini excavator with the digging power of a full-size machine. With an operating weight around 7.5 metric tons and a dig depth exceeding 4.5 meters, it became a popular choice for contractors needing versatility in confined spaces.
Komatsu, founded in Japan in 1921, has built a reputation for durable hydraulic systems and robust undercarriage engineering. The PC75 was widely distributed across Asia, Europe, and North America, and many units remain in active service or restoration.
Undercarriage Rollers and Their Role
The undercarriage of the PC75 includes track rollers, carrier rollers, idlers, sprockets, and track chains. Track rollers—also known as bottom rollers—support the weight of the machine and guide the track as it moves along the ground. Carrier rollers—top rollers—support the upper portion of the track and maintain tension.
Typical roller configuration:

• 5 to 6 bottom rollers per side
  
• 1 to 2 carrier rollers per side
  
• Sealed and lubricated for long service life
  
• Mounted to track frame via bolt-on brackets
  

Rollers are critical for maintaining track alignment, reducing vibration, and distributing weight evenly. Worn or seized rollers can lead to track derailment, uneven wear, and increased fuel consumption.
Common Roller Issues and Symptoms
As the PC75 ages, its rollers may exhibit several failure modes:

• Seized rollers due to bearing failure
  
• Leaking seals and loss of lubrication
  
• Flat spots from prolonged stationary loads
  
• Excessive play or wobble during travel
  
• Uneven track tension or misalignment
  

Operators may notice increased noise, vibration, or difficulty tracking straight. In one case, a contractor in Queensland reported that his PC75 veered left during travel. Inspection revealed two seized rollers on the right side, causing drag and imbalance.
Inspection and Diagnosis Procedure
Routine undercarriage inspection should include:

• Visual check for oil leaks around roller seals
  
• Manual rotation test to detect stiffness or grinding
  
• Measurement of roller diameter and wear pattern
  
• Check for lateral movement or loose mounting bolts
  
• Comparison of roller height to adjacent units
  

Use a pry bar to test roller play and a caliper to measure wear. If a roller fails to rotate freely or shows signs of seal failure, replacement is recommended.
Replacement Strategy and Sourcing
When replacing rollers on the PC75:

• Use OEM or high-quality aftermarket rollers with sealed bearings
  
• Replace in pairs to maintain balance and wear consistency
  
• Torque mounting bolts to factory spec (typically 120–150 ft-lbs)
  
• Clean mounting surfaces and apply anti-seize compound
  
• Inspect adjacent components (track links, idlers) for collateral wear
  

Some restorers opt to replace all bottom rollers during undercarriage overhaul, especially if the machine operates in abrasive terrain. A fleet manager in Alberta reported improved fuel efficiency and smoother travel after full roller replacement on three PC75 units.
Carrier Rollers and Load Distribution
Carrier rollers support the top of the track and help maintain proper tension. Though they wear more slowly than bottom rollers, they can still seize or flatten over time.
Carrier roller service tips:

• Inspect for seal leakage and bearing noise
  
• Replace if flat spots or excessive play are present
  
• Use thread locker on mounting bolts to prevent loosening
  
• Grease pivot points if applicable (some models are sealed-for-life)
  

In one restoration project, a PC75 used for slope grading showed excessive track sag. Replacing worn carrier rollers restored proper tension and reduced track slap during travel.
Preventive Maintenance and Operating Tips
To extend roller life:

• Clean undercarriage daily, especially in mud or gravel
  
• Avoid sharp turns on hard surfaces
  
• Maintain proper track tension (check weekly)
  
• Grease pivot points and inspect seals quarterly
  
• Rotate machine position during long idle periods to prevent flat spots
  

Use of rubber track pads can reduce vibration and wear on rollers, especially in urban environments.
Field Stories and Practical Solutions
In 2022, a utility crew in Ohio noticed excessive vibration during trenching. After inspecting the PC75’s undercarriage, they found two bottom rollers had seized and one carrier roller had collapsed. Replacing all three restored smooth operation and reduced operator fatigue.
Another example comes from a vineyard in California, where a PC75 was used for irrigation trenching. The machine began pulling to one side. A quick inspection revealed uneven roller wear due to constant turning in tight rows. The team replaced the affected rollers and began alternating turn direction to balance wear.
Conclusion and Recommendations
Rollers are a vital part of the Komatsu PC75’s undercarriage system. Their condition directly affects tracking, fuel efficiency, and operator comfort. With regular inspection and timely replacement, the machine can maintain peak performance across a wide range of terrain.
Recommendations include:

• Inspect rollers monthly and replace any seized or leaking units
  
• Use OEM or high-quality aftermarket parts for durability
  
• Replace in pairs to maintain balance
  
• Monitor track tension and adjust as needed
  
• Document roller replacements and service intervals
  

With proper care, the PC75 remains a reliable and agile excavator—capable of navigating tight spaces and tough ground with the smoothness and precision Komatsu is known for.