Diagnosing Starting Issues on the Kobelco SK35-2 Mini Excavator

[MikePhua]

The Kobelco SK35-2 and Its Compact Utility Legacy
The Kobelco SK35-2 is a compact mini excavator developed in the late 1990s as part of Kobelco’s push into the global light equipment market. With an operating weight of approximately 3,500 kg and a dig depth of over 3 meters, the SK35-2 was designed for urban construction, landscaping, and utility trenching. Powered by a small diesel engine—typically a Yanmar or Mitsubishi unit depending on market—it balances fuel efficiency with hydraulic responsiveness.
Kobelco, a division of Kobe Steel Ltd., has been producing excavators since the 1930s and is known for its innovation in hydraulic systems and emissions control. The SK series has sold tens of thousands of units globally, with the SK35-2 remaining a workhorse in rental fleets and small contractor operations.
Terminology Notes

• Glow Plug: A heating element in diesel engines that pre-warms the combustion chamber for cold starts.
  
• Starter Solenoid: An electromagnetic switch that activates the starter motor when the ignition key is turned.
  
• Fuel Cutoff Solenoid: A valve that controls fuel flow to the injection pump, often energized during engine start.
  
• Cranking Voltage: The voltage available to the starter motor during engine turnover, typically above 10.5V under load.
  

Common Starting Symptoms and Initial Observations
Operators of the SK35-2 have reported a range of starting issues, including:

• Engine cranks but fails to fire
  
• Starter clicks but does not engage
  
• No response when key is turned
  
• Starts intermittently, especially in cold weather
  
• Requires manual override or bypass to start
  

In one case in British Columbia, a landscaper noted that his SK35-2 would only start after tapping the starter with a wrench. Eventually, the starter solenoid was found to be corroded internally, causing intermittent contact.
Electrical System Checks and Battery Health
Starting issues often begin with the electrical system. Recommended steps:

• Measure battery voltage at rest (should be 12.6V or higher)
  
• Check cranking voltage during start attempt (should not drop below 10.5V)
  
• Inspect battery terminals for corrosion or loose connections
  
• Test starter solenoid for continuity and voltage drop
  
• Verify ground strap integrity between engine block and frame
  

A technician in Ohio found that a weak ground strap caused voltage drop during cranking, preventing the starter from engaging fully. Replacing the strap restored reliable starts.
Glow Plug and Cold Start Circuit Diagnosis
In colder climates, glow plug performance is critical. The SK35-2 typically uses a timed glow plug circuit activated by the key switch. To test:

• Measure voltage at glow plug terminal during preheat cycle
  
• Check glow plug resistance (typically 0.6–1.2 ohms)
  
• Inspect relay and timer module for proper function
  
• Listen for audible click when glow plug relay activates
  

In a winter job in Maine, an SK35-2 failed to start below freezing. The glow plug relay was found to be stuck open, preventing preheat. Replacing the relay resolved the issue.
Fuel System Integrity and Solenoid Function
Diesel engines require clean, pressurized fuel delivery. Key checks:

• Inspect fuel lines for air leaks or cracks
  
• Prime fuel system manually if equipped with hand pump
  
• Test fuel cutoff solenoid for voltage and actuation
  
• Check return line for unrestricted flow
  

A contractor in Texas discovered that his SK35-2’s fuel cutoff solenoid was receiving only 9V due to a worn ignition switch. The low voltage prevented full actuation, starving the engine of fuel during cranking.
Starter Motor and Mechanical Engagement
If the starter motor fails to engage or spins weakly:

• Bench test starter for torque and current draw
  
• Inspect pinion gear and flywheel teeth for wear
  
• Check solenoid plunger for sticking or misalignment
  
• Replace brushes and clean commutator if worn
  

In a repair shop in Melbourne, a rebuilt starter was installed on an SK35-2 but failed to crank. The solenoid plunger was misaligned during assembly, causing binding. Realignment restored function.
Bypass Techniques and Emergency Start Options
In field conditions, technicians may use bypass methods:

• Jump starter solenoid directly with insulated screwdriver
  
• Apply 12V to fuel solenoid manually to verify actuation
  
• Use remote starter switch to isolate ignition circuit
  

These methods should only be used for diagnosis and not as permanent solutions. A fleet manager in Alberta trained his crew to use a bypass switch during emergencies but mandated full repair within 24 hours.
Preventive Maintenance and Long-Term Reliability
To avoid future starting issues:

• Replace glow plugs every 1,000 hours or as needed
  
• Clean battery terminals quarterly
  
• Inspect starter wiring harness annually
  
• Use fuel additives in winter to prevent gelling
  
• Log start attempts and failures for trend analysis
  

A rental company in Florida implemented a start log system for their mini excavators. Machines with more than three failed starts in a week were flagged for inspection. This reduced no-start incidents by 60% over six months.
Final Thoughts
Starting issues on the Kobelco SK35-2 are often a blend of electrical, fuel, and mechanical factors. With methodical testing and attention to voltage, solenoid function, and fuel delivery, most problems can be resolved without major teardown. In compact excavators, reliability starts with the first turn of the key—and understanding the system behind it is the key to uptime.