Getting Started with a Mitsubishi MS120/8 Excavator and Kawasaki MX80CA Swing Motor

[MikePhua]

The Mitsubishi MS120/8 and Its Mechanical Heritage
The Mitsubishi MS120/8 excavator is a mid-sized machine from a manufacturer that once played a significant role in Japan’s heavy equipment industry. Mitsubishi Heavy Industries, with roots tracing back to the 19th century, produced a range of construction equipment before gradually shifting focus toward aerospace, shipbuilding, and energy sectors. The MS120/8 was part of a generation of excavators built for durability and simplicity, often found in forestry, roadwork, and utility trenching.
Though no longer in production, the MS120/8 remains in service across Asia, Europe, and North America, especially in rural or independent operations. Its mechanical systems are straightforward, but documentation can be scarce, especially for imported or gray-market units.
Terminology Annotation
- Swing Motor: A hydraulic motor that powers the rotation of the upper structure of the excavator.
- Axial Piston Motor: A type of hydraulic motor where pistons move parallel to the drive shaft, offering high torque and efficiency.
- Gear Oil: A high-viscosity lubricant used in gearboxes and swing drives to reduce wear and dissipate heat.
- Dipstick Level: The marked range on a dipstick indicating proper fluid volume.
- Shop Manual: A technical document detailing service procedures, specifications, and diagrams for a specific machine.
Locating Technical Documentation
Finding a shop manual for the MS120/8 can be challenging due to its age and limited distribution. Many manuals are no longer in print or are held by regional dealers who serviced Mitsubishi equipment decades ago. However, several strategies can help:

• Visit local heavy equipment dealers and ask to view archived manuals; many will copy relevant pages
  
• Search for manuals from similar Mitsubishi models with shared components
  
• Contact salvage yards or auction houses that specialize in Japanese imports
  
• Join regional equipment forums or social media groups focused on vintage machinery
  
• Look for manuals in multiple languages, especially Japanese or Spanish, and use translation tools
  

Operators have reported success by identifying shared engine models—such as Mitsubishi S6S or S4E—and sourcing engine-specific manuals that include hydraulic and electrical schematics.
Understanding the Kawasaki MX80CA Swing Motor
The swing motor on the MS120/8 is a Kawasaki MX80CA-11A-01/220, an axial piston motor commonly used in excavators of this size. The nameplate also references a component number C852-50000, which may correspond to a specific application or mounting configuration.
When the swing motor is low on fluid, the recommended lubricant is typically 80W-90 gear oil. This is a standard choice for swing drives across many brands, including Komatsu, Hitachi, and Kobelco. The oil should be filled to the dipstick line or sight glass, depending on the motor’s design.
If the fluid level drops repeatedly, it may indicate:

• A failed shaft seal allowing oil to leak into the swing bearing tub
  
• A cracked housing or loose drain plug
  
• Internal wear causing pressure loss and overheating
  

In such cases, the motor may need to be removed and rebuilt. Rebuilding an axial piston motor involves replacing seals, inspecting pistons and swash plates, and verifying tolerances. This should be done by a qualified hydraulic technician with access to Kawasaki service specifications.
Field Advice and Practical Tips
Operators with experience on the MS120 series note that the machine is slow but strong. Its hydraulic system is simple, and the swing motor, while not fast, is reliable when maintained properly. The bucket pins are 55 mm—smaller than modern standards—which can make sourcing attachments more difficult.
One technician in Ireland recalled putting thousands of hours on an MS120 with direct mechanical linkages from the control levers. He emphasized that oil is the cheapest insurance for these machines and that regular top-offs and inspections go a long way.
Another operator in Spain observed a fleet of MS120s still working in rural infrastructure projects, a testament to their longevity and mechanical resilience.
Recommendations for New Owners
For those new to excavator ownership, especially with older machines:

• Keep a logbook of fluid changes, inspections, and repairs
  
• Use high-quality gear oil and hydraulic fluid from reputable brands
  
• Inspect seals and hoses monthly for signs of wear or leakage
  
• Learn basic hydraulic principles to understand system behavior
  
• Build relationships with local mechanics and parts suppliers
  
• Carry spare filters, O-rings, and common fittings on-site
  

Even without a full manual, many service tasks can be performed with careful observation and mechanical intuition. The MS120/8 is forgiving in many ways, and its systems are accessible compared to newer, electronically controlled models.
Conclusion
Owning a Mitsubishi MS120/8 excavator with a Kawasaki MX80CA swing motor is a journey into the world of legacy machinery. While documentation may be scarce, the machine’s design favors simplicity and durability. With the right oil, a bit of detective work, and a willingness to learn, even a first-time operator can keep this classic digger running strong. In heavy equipment, knowledge grows with every bolt turned—and every drop of oil poured with purpose.