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Compact Power with a Proven Legacy
The Komatsu D21-6 is part of the D21 series of compact crawler dozers, first introduced in the 1980s and refined through the early 2000s. Designed for small-scale grading, landscaping, and agricultural work, the D21-6 variant features hydrostatic drive, a 4-cylinder diesel engine, and a low-profile design ideal for tight spaces. Komatsu, founded in 1921 in Japan, has long been a global leader in earthmoving equipment, and the D21 series remains one of its most enduring compact dozer platforms.
Core Specifications and Performance
The D21-6 offers a balance of maneuverability and pushing power. Key specs include:
Undercarriage and Wear Components
In one example, a D21-6 was fitted with new sprockets, rollers, and chains, while retaining the original grousers. This setup is common in rebuilds where the track shoes remain structurally sound. The undercarriage is a critical wear zone, and replacing these components can extend service life by thousands of hours.
Operators should inspect:
Cab Design and Operator Comfort
The D21-6 typically features an open ROPS (Roll-Over Protective Structure) with minimal shielding. While this offers excellent visibility, it exposes the operator to weather and debris. Some units are retrofitted with soft cabs or canopy enclosures for winter use. The seat and control layout are simple but functional, with mechanical linkages and analog gauges.
Hydraulic System and Blade Control
The dozer blade is controlled by a single hydraulic lever, offering lift and tilt functions. The system uses a gear pump and open-center valves, making it easy to service and compatible with standard hydraulic fluids. Blade responsiveness is adequate for light grading, though not as refined as larger dozers with multi-function joysticks.
Market Value and Resale Trends
As of 2025, a well-maintained D21-6 with recent undercarriage work and functional hydraulics typically sells for $8,000 to $12,000 USD, depending on location and hours. Machines with documented service history and clean frames command higher prices. The D21 series remains popular among small contractors, farmers, and landowners due to its simplicity and low operating costs.
Common Issues and Maintenance Tips
Conclusion
The Komatsu D21-6 is a compact, reliable dozer with a strong reputation for durability and ease of maintenance. While it lacks the electronic sophistication of newer models, its mechanical simplicity makes it ideal for owner-operators and small-scale earthmoving tasks. With proper care and attention to undercarriage and hydraulic systems, the D21-6 can deliver years of dependable service across a wide range of applications.
The Komatsu D21-6 is part of the D21 series of compact crawler dozers, first introduced in the 1980s and refined through the early 2000s. Designed for small-scale grading, landscaping, and agricultural work, the D21-6 variant features hydrostatic drive, a 4-cylinder diesel engine, and a low-profile design ideal for tight spaces. Komatsu, founded in 1921 in Japan, has long been a global leader in earthmoving equipment, and the D21 series remains one of its most enduring compact dozer platforms.
Core Specifications and Performance
The D21-6 offers a balance of maneuverability and pushing power. Key specs include:
- Engine: Komatsu 4D95S diesel, ~40 hp
- Operating weight: ~8,000 lbs (3,630 kg)
- Blade width: ~6 ft (1.8 m)
- Transmission: Hydrostatic, twin-lever control
- Track type: Steel grousers, with optional rubber pads
Undercarriage and Wear Components
In one example, a D21-6 was fitted with new sprockets, rollers, and chains, while retaining the original grousers. This setup is common in rebuilds where the track shoes remain structurally sound. The undercarriage is a critical wear zone, and replacing these components can extend service life by thousands of hours.
Operators should inspect:
- Track tension and alignment
- Roller wear and seal integrity
- Sprocket tooth profile
- Grouser bolt torque and shoe condition
Cab Design and Operator Comfort
The D21-6 typically features an open ROPS (Roll-Over Protective Structure) with minimal shielding. While this offers excellent visibility, it exposes the operator to weather and debris. Some units are retrofitted with soft cabs or canopy enclosures for winter use. The seat and control layout are simple but functional, with mechanical linkages and analog gauges.
Hydraulic System and Blade Control
The dozer blade is controlled by a single hydraulic lever, offering lift and tilt functions. The system uses a gear pump and open-center valves, making it easy to service and compatible with standard hydraulic fluids. Blade responsiveness is adequate for light grading, though not as refined as larger dozers with multi-function joysticks.
Market Value and Resale Trends
As of 2025, a well-maintained D21-6 with recent undercarriage work and functional hydraulics typically sells for $8,000 to $12,000 USD, depending on location and hours. Machines with documented service history and clean frames command higher prices. The D21 series remains popular among small contractors, farmers, and landowners due to its simplicity and low operating costs.
Common Issues and Maintenance Tips
- Hydrostatic drive: Check for fluid leaks and monitor pump noise. Use Komatsu-specified hydraulic oil for longevity.
- Electrical system: Inspect wiring harnesses for corrosion, especially near the starter and battery terminals.
- Cooling system: Flush radiator every 1,000 hours and inspect hoses for cracking.
- Fuel system: Replace filters regularly and bleed air after service to prevent hard starts.
Conclusion
The Komatsu D21-6 is a compact, reliable dozer with a strong reputation for durability and ease of maintenance. While it lacks the electronic sophistication of newer models, its mechanical simplicity makes it ideal for owner-operators and small-scale earthmoving tasks. With proper care and attention to undercarriage and hydraulic systems, the D21-6 can deliver years of dependable service across a wide range of applications.
