Restoring and Maintaining a 1985 Komatsu D31A-17 Dozer

[MikePhua]

A Compact Dozer with Enduring Utility
The Komatsu D31A-17, introduced in the early 1980s, is a compact crawler dozer designed for grading, land clearing, and light construction. With an operating weight around 16,000 lbs and a 4-cylinder diesel engine producing approximately 65 horsepower, the D31A-17 was built for maneuverability and reliability. Its six-way blade and hydrostatic transmission made it a versatile choice for contractors and landowners alike. Komatsu’s Series 17 machines were known for their robust undercarriage and straightforward mechanical systems, which contributed to their long service life.
Hydraulic Control Valve Leaks and Diagnosis
One common issue in aging D31A-17 units is a slow hydraulic leak beneath the blade control lever—specifically when operating the side-to-side tilt function. This leak typically originates from the blade control valve, also referred to as the six-way valve. The leak may only produce a few drops during operation, but over time it can attract grime and obscure the source.
Key symptoms include:

• Fluid dripping from the base of the control lever
  
• Accumulated dirt and oil around the valve housing
  
• No leak during idle or other blade movements
  

Terminology Clarification

• Six-Way Blade: A dozer blade that can move up/down, tilt left/right, and angle left/right.
  
• Blade Control Valve: A hydraulic valve assembly that directs fluid to the blade cylinders based on operator input.
  
• Cylinder/Piston Housing: The casing around the hydraulic actuator that moves the blade.
  
• Hydraulic Drip: A minor leak that occurs only during specific valve actuation, often due to worn seals.
  

Repair Considerations and Practical Advice
For machines used lightly—such as for trail maintenance or personal land clearing—a minor leak may not justify immediate repair. However, if the leak worsens or affects blade responsiveness, addressing it becomes necessary. Repairing the blade control valve involves:

• Removing the console cover to access the valve body
  
• Cleaning the area thoroughly to identify the leak source
  
• Replacing O-rings or spool seals within the valve
  
• Inspecting the lever linkage for wear or misalignment
  

Seal kits for the Series 17 control valves are still available through Komatsu parts dealers or aftermarket suppliers. When replacing seals, use hydraulic-rated grease and torque fasteners to spec. If the valve body is cracked or pitted, replacement may be more cost-effective than rebuilding.
Finding Manuals and Technical Support
Operators seeking service manuals for the D31A-17 often turn to online marketplaces. European sellers frequently list Series 17 manuals on auction platforms, and setting up alerts can help locate them. Manuals provide exploded diagrams, torque specs, and hydraulic schematics essential for valve repair and general maintenance.
Preventive Measures and Long-Term Care

• Keep the control valve area clean to monitor leaks
  
• Use ISO 46 hydraulic oil and change every 500 hours
  
• Inspect blade cylinder seals annually
  
• Grease all blade pivot points monthly
  
• Store the machine under cover to reduce moisture intrusion
  

In one restoration story, a landowner in New York acquired a well-maintained 1985 D31A-17 with only minor hydraulic seepage. After cleaning the valve and replacing two O-rings, the leak stopped entirely. The machine has since been used for trail grading and snow clearing with no further issues.
Conclusion
The Komatsu D31A-17 remains a capable and dependable dozer decades after its release. While small hydraulic leaks around the blade control valve are common in older units, they can be managed or repaired with basic tools and seal kits. With proper care, this compact crawler continues to serve as a practical solution for light-duty earthmoving and land management.