Kobelco SK120: A Reliable Mid-Size Excavator with Staying Power

[MikePhua]

Introduction to the SK120
The Kobelco SK120 is a well-regarded mid-size excavator with a reputation for reliability, simplicity, and surprising power for its size. Manufactured during the late 1980s through the early 2000s, the SK120 has proven to be a strong performer in light-to-medium construction, drainage, forestry, and utility work. Despite its age, many units are still operating around the world, especially in owner-operator and rural fleets.
Its compact profile, straightforward design, and long service life have made it a favorite among seasoned operators who appreciate machines that don’t require complex electronics to get the job done.
Performance and Capabilities
Weighing approximately 12 metric tons (26,000 lbs) and powered by a 4-cylinder Isuzu diesel engine generating around 85–90 horsepower, the SK120 is capable of lifting, digging, and trenching with surprising agility. Its hydraulic performance is often praised for smooth and responsive operation.
Users often report that it "just works"—a notable strength when compared to more recent models which may be hobbled by electronic diagnostics or complex emissions systems. In remote locations or with limited access to service techs, simplicity is gold.
An Australian excavation contractor once remarked, “The SK120 may not be flashy, but it’ll outlast anything with a screen. When you're a hundred kilometers from the nearest town, that matters.”
Common Issues and How to Address Them
Like all machines, the SK120 is not without its quirks:

• Hydraulic Drift or Weakness: Over time, older units may suffer from hydraulic cylinder bypass or main control valve leakage, leading to slow or "soft" movements. Rebuilding cylinders or resealing the valve block typically restores performance.
  
• Throttle Control Malfunctions: On units with electronic stepper motors, throttle problems are not uncommon. When the system fails, operators often retrofit a mechanical throttle cable as a cost-effective workaround.
  
• Underrated Undercarriage Wear: Although the SK120 is known for its strong swing and digging capability, its undercarriage—if neglected—can lead to track tension issues or accelerated wear. Regular inspection of rollers, sprockets, and idlers is essential.
  

A notable case in British Columbia involved an SK120 used for slope stabilization. After over 12,000 hours, the machine began showing hydraulic fatigue. Yet, instead of retiring it, the owner spent $5,000 on a full reseal and continued working with it on light-duty tasks. “It still digs cleaner than some new machines,” he said.
Gray Market Variants
Several versions of the SK120 were imported from Japan as gray market machines. These versions sometimes lack English labeling or differ slightly in cab controls and safety features. While perfectly serviceable, parts availability can vary, and wiring diagrams may not match North American manuals. Buyers of such models should be prepared for creative solutions when troubleshooting.
Why It Remains a Favorite

• Simplicity: No complex electronics, minimal sensors, and a mechanical fuel injection system that is easy to service.
  
• Longevity: Many operators report 10,000+ hours of use with only standard maintenance and periodic resealing.
  
• Fuel Economy: Even by modern standards, the SK120 is a fuel-sipping workhorse, making it ideal for low-overhead operations.
  
• Good Visibility and Operator Comfort: While not luxurious, the cab offers good sightlines and decent space for its era.
  

As one retired operator from Iowa quipped, “If the SK120 had a face, it would have wrinkles and scars—but it’d still be grinning while it digs.”
In Retrospect
The Kobelco SK120 has quietly earned its place in heavy equipment history not because it led with innovation, but because it delivered honest, reliable work over decades. In an age of planned obsolescence and over-engineered machinery, the SK120 is a testament to the enduring value of simplicity.
Whether you're grading a driveway, trenching a sewer line, or clearing brush, if you find a well-maintained SK120, chances are it’ll still get the job done—and ask for little in return.