Kobelco SK220 (Mk III) Excavator: Insights, Common Hydraulic Issues & User Feedback

[MikePhua]

Overview of the SK220 Mk III
The Kobelco SK220 Mk III is a mid‑sized crawler excavator introduced in the early 1990s, part of the SK200/SK220 Mark III series. It features a 4‑cylinder Mitsubishi 6D15 turbocharged diesel engine (not Volvo), delivering dependable performance in excavation and earthmoving roles . Designed with robust build quality and Kawasaki hydraulic pumps, it catered to both private ownership and small fleet use globally.

Typical Hydraulic Performance Concerns
A recurring issue reported by field operators is weak boom and stick performance, particularly when operating while the tracks are engaged. In some cases, moving the machine forward or steering at the same time noticeably improves hydraulic responsiveness. This suggests a potential imbalance or inefficiency in the hydraulic pump or control valve regimes .
One seasoned technician traced such symptoms to the dual-pump configuration: one pump dedicated to travel, the other to attachments. If the attachment pump slips or the regulator spool binds, you’ll have poor lift/arm performance unless travel engages that second pump temporarily—creating a curious "power only when moving" behavior .

Fault Diagnosis and Field Inspection Tips

• Check for pump regulator binding: The regulator should maintain minimal preload via a small internal spring. A sloppy or free-floating actuating lever indicates contamination or internal wear.
  
• Inspect the pump’s displacement piston yoke: Over time, thread loosening can reduce stroke capacity. Carefully applying a tiny drop of blue Loctite to stabilize the threads (avoiding contamination into the pump) can restore displacement.
  
• Avoid full pump teardown unless confirmed faulty: Many problems stem from regulator binding or minor misadjustments—full rebuilds are rarely needed initially.
  
• Track RPM testing: With each track raised, count revolutions while free-wheeling. Significant divergence indicates motor or final-drive issues—not just hydraulic pump failure .
  

Real-World Troubleshooting Summary
List of Recommended Initial Checks

• Observe whether attachment performance improves when machine is in motion.
  
• Free-wheel each track and compare revolutions to detect travel motor issues.
  
• Disassemble regulator (with caution) to check internal spring tension and movement.
  
• Inspect and secure the displacement piston threads; avoid overt tightening.
  
• Clean surrounding hydraulics and regulator to remove internal debris before concluding.
  

Technical Glossary

• Dual Pump System: In SK220 Mk III, attachments and travel use separate pumps fed from a shared reservoir.
  
• Regulator (Displacement Control Assembly): Hydraulic component that sets pump output pressure via small preload spring.
  
• Displacement Piston Yoke: Connects regulator to swash plate; vital for stroke control. May loosen over time.
  
• Independent Travel Function: Feature allowing travel motor to operate separately from attachments.
  

Case Anecdotes from Owners

• A Tasmanian user initially suspected engine deceit due to poor boom force. On inspection, the displacement yoke had lost preload. A minor adjustment restored full hydraulic force without replacing the pump .
  
• Another owner noted the machine handled rockbreaking well—despite undercarriage wear—until combined lift and track movement triggered better performance. This pointed again to pump regulator thematics, rather than engine performance .
  

Preventive Measures & Maintenance Advice

• Change hydraulic fluid and filters regularly to prevent debris jams inside displacement regulators.
  
• Inspect regulator spring tension annually, especially if attachment operation feels sluggish.
  
• Check and secure piston yoke threads during routine service intervals.
  
• Monitor travel motor RPM balance via idle wheels for early signs of travel motor fatigue.
  

Conclusion: Smart Diagnostics Avoid Costly Pump Rebuilds
Although the Kobelco SK220 Mk III may appear underpowered hydraulically, many performance issues originate from dual-pump design quirks and regulator displacement problems, not engine failure. By methodically diagnosing regulator spring preload, yoke tension, and RPM balance, operators can often restore full hydraulic functionality without draining major expense on pump replacement.
Experienced operators and technicians emphasize understanding how the attachment and travel systems interact—especially under load—to unearth performance quirks rooted in OEM design rather than abuse. For buyers and owners, that awareness can make the difference between a good deal on a fairly priced machine and an unexpected hydraulic overhaul.