Sumitomo Excavators and the Enduring Legacy of Japanese Engineering

[MikePhua]

The Origins of Sumitomo Construction Machinery
Sumitomo Heavy Industries, a core member of the centuries-old Sumitomo Group, began manufacturing construction equipment in the mid-20th century. By the 1960s, the company had entered the hydraulic excavator market, leveraging its expertise in precision machinery and metallurgy. Early models like the LS series were built with mechanical simplicity and durability in mind, often powered by reliable Isuzu diesel engines and featuring robust undercarriages suited for forestry, demolition, and general excavation.
Sumitomo’s excavators gained traction globally, especially in Asia, Australia, and parts of North America. By the 1980s, the LS1600 and LS280 models were widely used in mid-scale construction and land clearing. These machines were known for their straightforward hydraulic systems, mechanical lever controls, and steel track chains that could withstand harsh terrain.
Mechanical Characteristics and Operating Behavior
Sumitomo excavators from the 1970s and 1980s typically featured:

• Operating weight: ~7,500 kg for LS1600
  
• Engine: 4-cylinder Isuzu diesel, naturally aspirated or turbocharged
  
• Hydraulic system: Open-center with gear or piston pumps
  
• Controls: Mechanical levers with pilot assist in later models
  
• Undercarriage: Steel tracks with bolt-on pads
  
• Swing system: Hydraulic motor with planetary reduction
  
• Bucket capacity: ~0.3–0.5 cubic meters depending on configuration
  

Terminology notes:

• Open-center hydraulic system: A design where fluid flows continuously until a valve is actuated, common in older machines.
  
• Planetary reduction: A gear system that multiplies torque while reducing speed, used in swing and travel motors.
  

In Ontario, a contractor used an LS1600 to clear brush and dig trenches on a remote property. Despite its age, the machine performed reliably, with only minor seepage from the boom cylinder and occasional track tension adjustments.
Common Issues and Field Repairs
Older Sumitomo excavators are mechanically sound but require regular attention to seals, hoses, and undercarriage components. Common problems include:

• Hydraulic cylinder seepage due to hardened seals
  
• Track chain stretch and sprocket wear
  
• Swing motor lag from internal leakage
  
• Rough idle from injector imbalance or fuel contamination
  
• Electrical corrosion in starter and alternator circuits
  

Suggested solutions:

• Repack cylinders with OEM seal kits or high-quality aftermarket replacements
  
• Replace sprockets and chains as a set to maintain pitch alignment
  
• Flush hydraulic system and replace filters every 500 hours
  
• Clean fuel tank and lines to prevent injector fouling
  
• Upgrade wiring harness with sealed connectors and heat shrink
  

In South Africa, a vineyard crew rebuilt their LS280’s swing motor after noticing delayed rotation. The internal seals had degraded, allowing pressure loss. After resealing and flushing the system, the swing returned to full responsiveness.
Parts Availability and Restoration Strategy
While Sumitomo excavators are no longer as common in North America, parts remain accessible through specialized suppliers and cross-referencing with Link-Belt and Case models, which Sumitomo manufactured under OEM agreements.
Restoration tips:

• Identify engine model and source parts from Isuzu dealers
  
• Use hydraulic fittings compatible with JIS or BSP threads
  
• Replace track components with aftermarket equivalents from Berco or ITM
  
• Scan manuals for fluid specs and torque values
  
• Document all part numbers and create a service log for future reference
  

Suggested spares to stock:

• Hydraulic seal kits for boom, arm, and bucket cylinders
  
• Track rollers, idlers, and sprockets
  
• Fuel and oil filters
  
• Starter motor and alternator
  
• Electrical connectors and relays
  

In New Zealand, a contractor restored a 1985 LS1600 using salvaged parts from a retired forestry machine. The rebuilt excavator now operates on a small quarry, handling rock and overburden with ease.
Operator Stories and Field Wisdom
In Florida, a demolition crew used a Sumitomo excavator to dismantle a concrete warehouse. The machine’s mechanical controls allowed precise bucket placement, and its steel tracks handled debris without damage. After upgrading the hydraulic pump, cycle times improved noticeably.
In Poland, a snow-clearing team repurposed an LS280 for winter ditch maintenance. By fitting a custom V-shaped bucket and reinforcing the boom, they adapted the machine for seasonal work and extended its service life by over a decade.
Conclusion
Sumitomo excavators represent a blend of Japanese engineering discipline and field-tested durability. Though many models are now considered vintage, their mechanical simplicity and robust design continue to earn respect among operators and restorers. With proper maintenance, thoughtful upgrades, and a steady supply of parts, these machines remain capable of tackling earthmoving tasks with precision and reliability. Whether digging in clay or clearing rubble, a well-kept Sumitomo still holds its own—decades after rolling off the line.