Komatsu D20 and D21 Undercarriage Parts Availability and Restoration Insights

[MikePhua]

The Komatsu D20 and D21 Dozer Lineage
The Komatsu D20 and D21 compact crawler dozers were introduced in the 1980s as part of Komatsu’s strategy to offer maneuverable, lightweight machines for grading, land clearing, and small-scale construction. Built in Japan and exported globally, these models became popular in Southeast Asia, North America, and Australia due to their reliability, ease of transport, and mechanical simplicity.
The D20 typically featured a 40 HP Komatsu diesel engine, while the D21 offered slightly more power and a wider blade. Both models used a direct mechanical transmission, lever-operated steering clutches, and a rigid undercarriage with sealed track chains. Their compact size made them ideal for vineyard work, trail maintenance, and residential site prep.
By the late 1990s, production slowed as newer hydrostatic models entered the market. However, the D20 and D21 remain in use today, especially among owner-operators and restoration enthusiasts.
Undercarriage Components and Wear Patterns
The undercarriage of the D20/D21 includes:

• Track chains (sealed or dry type)
  
• Track rollers (single or double flange)
  
• Carrier rollers
  
• Idlers and recoil springs
  
• Sprockets
  
• Track shoes (bolt-on or welded)
  

Common wear issues:

• Sprocket teeth rounding due to chain stretch
  
• Roller bearing failure from lack of lubrication
  
• Track shoe cracking from impact or fatigue
  
• Idler seal leakage and spring collapse
  
• Chain pin and bushing wear leading to pitch elongation
  

A forestry operator in Oregon reported that his D21 began tracking unevenly. Inspection revealed a seized carrier roller and a worn sprocket. Replacing both restored alignment and reduced vibration during grading.
Sourcing New and Used Parts
Finding parts for legacy Komatsu dozers can be challenging but not impossible. Options include:

• Authorized Komatsu dealers with legacy inventory
  
• Aftermarket suppliers specializing in vintage equipment
  
• Salvage yards and dismantlers with donor machines
  
• Online marketplaces and auction platforms
  
• Custom fabrication for hard-to-find components
  

Recommended sourcing strategy:

• Identify part numbers using the original service manual
  
• Verify compatibility across D20, D21, and D21A variants
  
• Inspect used parts for wear limits and structural integrity
  
• Prioritize OEM or high-quality aftermarket brands for critical components
  
• Consider bulk purchases to reduce shipping costs
  

A contractor in Queensland sourced a full undercarriage kit for his D20 from a dismantler in New Zealand. The kit included track chains, rollers, and sprockets—all refurbished and pressure-tested. The rebuild extended the machine’s life by over 2,000 hours.
Restoration Tips and Upgrade Paths
When restoring a D20 or D21:

• Replace all undercarriage components at once to ensure even wear
  
• Use sealed and lubricated chains if available—they reduce maintenance
  
• Upgrade to polyurethane track pads for reduced ground disturbance
  
• Install greaseable rollers and idlers for longer service intervals
  
• Reinforce blade mounts and pivot bushings during teardown
  

Some owners retrofit LED lighting, canopy frames, and hydraulic blade tilt kits to modernize their machines. In one case, a vineyard operator in California added a GPS receiver and slope sensor to his D21 for precision grading between rows.
Preventive Maintenance and Service Intervals
To extend undercarriage life:

• Inspect track tension weekly and adjust as needed
  
• Clean undercarriage daily in muddy or sandy conditions
  
• Grease rollers and idlers every 50 hours
  
• Monitor sprocket wear and replace before tooth tips round
  
• Check track shoe bolts for tightness monthly
  
• Drain and refill final drives annually
  

Using high-quality gear oil and keeping the machine stored under cover can significantly reduce corrosion and seal degradation.
Conclusion
The Komatsu D20 and D21 dozers remain valuable tools for compact earthmoving tasks, especially when properly maintained and restored. While undercarriage parts may be harder to source than for newer models, a combination of dealer support, aftermarket suppliers, and salvage networks keeps these machines alive. With thoughtful upgrades and disciplined service, the D20/D21 can continue to grade, push, and clear with the same tenacity they were built for decades ago.