MDI Yutani Excavators and the Challenge of Legacy Support

[MikePhua]

The Rise and Fall of MDI Yutani
MDI Yutani was once a respected name in the excavator industry, known for producing durable machines that served construction and forestry sectors across North America and Asia. The company emerged from a partnership between MDI (Machinery Development International) and Yutani Heavy Industries, a Japanese firm with roots in hydraulic technology and steel fabrication. During the 1980s and early 1990s, MDI Yutani excavators were widely distributed, especially in Canada and parts of the U.S., where their robust frames and reliable hydraulics earned them a loyal following.
However, by the late 1990s, the brand began to fade due to market consolidation, limited parts support, and competition from giants like Komatsu, Caterpillar, and Hitachi. MDI Yutani ceased production, leaving thousands of machines in operation but without a clear supply chain for parts or technical documentation.
Terminology Note

• Boom Cylinder: A hydraulic actuator that raises and lowers the excavator’s boom.
  
• Swing Motor: Drives the upper structure of the excavator to rotate left or right.
  
• Final Drive: The gear assembly that powers the tracks, converting hydraulic pressure into movement.
  
• Pilot Control: A low-pressure hydraulic system that actuates the main control valves.
  

Common Issues with Aging MDI Yutani Machines
Owners of older MDI Yutani excavators often face challenges such as:

• Difficulty sourcing replacement parts for hydraulic pumps, swing motors, and electrical components
  
• Lack of service manuals or wiring diagrams
  
• Uncertainty about fluid specifications and filter compatibility
  
• Inconsistent labeling of model numbers and serial plates
  

One operator in British Columbia shared a story of inheriting a Yutani excavator from his father’s logging operation. The machine ran well but had a leaking boom cylinder. After months of searching, he discovered that the seal kit matched a Komatsu PC200 series, suggesting shared component sourcing during the original manufacturing phase.
Identifying Compatible Parts and Cross-Referencing
Many MDI Yutani excavators were built using components sourced from Japanese suppliers such as Kayaba, Toshiba, and Komatsu. This opens the door to cross-referencing parts with other brands. For example:

• Hydraulic pumps may match early Kayaba or Kawasaki units
  
• Swing motors often resemble those used in Hitachi EX series
  
• Filters can be matched by thread size and micron rating
  
• Electrical connectors may follow JIS standards used in other Japanese machines
  

Recommended steps for identifying compatible parts:

• Locate and photograph all serial plates and casting numbers
  
• Measure thread sizes and port configurations
  
• Compare component shapes and mounting patterns with known models
  
• Consult with hydraulic rebuild shops familiar with Japanese equipment
  

A technician in Oregon rebuilt a Yutani swing motor using seals from a Kobelco SK200, saving over $1,200 compared to custom machining.
Hydraulic System Behavior and Troubleshooting
Older Yutani excavators often exhibit sluggish hydraulic response, especially in cold weather or after long idle periods. This is typically caused by:

• Worn pilot control valves
  
• Contaminated hydraulic fluid
  
• Internal leakage in boom or arm cylinders
  
• Weak charge pressure from the main pump
  

Solutions include:

• Flushing the hydraulic system and replacing with ISO 46 or ISO 68 grade fluid depending on climate
  
• Installing inline filters with magnetic traps to catch metal debris
  
• Replacing pilot lines with modern braided hose to prevent collapse
  
• Testing pump output using flow meters and pressure gauges
  

In a 2022 field test, a rebuilt Yutani excavator showed a 35% improvement in cycle times after replacing the pilot valve block and upgrading the fluid to synthetic blend.
Electrical System Challenges and Workarounds
The electrical systems in MDI Yutani machines are often rudimentary, relying on analog gauges, relays, and simple fuse blocks. Over time, corrosion and vibration degrade connections, leading to intermittent faults.
Common symptoms include:

• Starter not engaging
  
• Gauges reading erratically
  
• Boom or arm functions failing intermittently
  
• Battery drain when machine is off
  

Recommended upgrades:

• Replace fuse blocks with marine-grade sealed units
  
• Install LED indicators to monitor voltage and current draw
  
• Use dielectric grease on all connectors
  
• Add a master disconnect switch to prevent parasitic drain
  

A contractor in Nova Scotia retrofitted his Yutani with a modern relay panel and digital voltmeter, eliminating electrical issues that had plagued the machine for years.
Operator Stories and Field Wisdom
In Alaska, a road-building crew used a Yutani excavator to clear permafrost terrain. Despite its age, the machine performed reliably after the swing motor was rebuilt and the hydraulic fluid upgraded. The operator noted that the machine’s steel was thicker than newer models, helping it resist damage from frozen debris.
Meanwhile, a demolition team in Texas repurposed a Yutani for concrete breaking. They fabricated a custom bracket to mount a hydraulic hammer, using dimensions from a Komatsu PC210. The machine ran for over 1,500 hours before needing final drive service.
Preserving and Restoring Legacy Machines
For those committed to keeping MDI Yutani excavators operational, the following strategies are effective:

• Partner with local hydraulic shops for seal kits and pump rebuilds
  
• Use online forums and salvage yards to locate donor machines
  
• Document all modifications and part numbers for future reference
  
• Consider converting electrical systems to 24V if original components are unavailable
  

A restoration project in Michigan involved repainting and rewiring a Yutani excavator for use in a municipal yard. The team sourced parts from three different brands and created a hybrid machine that continues to serve reliably.
Conclusion
MDI Yutani excavators may no longer be supported by a manufacturer, but their legacy lives on through the ingenuity of operators and technicians who keep them running. With careful cross-referencing, hydraulic expertise, and electrical upgrades, these machines can continue to perform in demanding environments. Their robust design and shared component heritage make them viable candidates for restoration and reuse—proof that even orphaned equipment can find new life with the right approach.