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The Hitachi EX100-2 and Its Place in Excavator History
The Hitachi EX100-2 was part of a pivotal generation of Japanese-built excavators that helped define the global mid-size market in the 1990s. With an operating weight of roughly 10 metric tons and a proven Isuzu diesel engine, the EX100-2 offered a balance of power, reliability, and serviceability. Hitachi Construction Machinery, founded in 1970, had by then become a major player in the earthmoving sector, with the EX series gaining traction across Europe, Asia, and North America.
The EX100-2 featured a hydraulic system built around pilot controls and a variable displacement pump, making it responsive and efficient for trenching, grading, and demolition work. However, as machines aged and parts availability shifted, many owners opted to retrofit or convert the hydraulic system—especially when dealing with solenoid failures or outdated control logic.
Hydraulic Conversion Kits and Common Pitfalls
Retrofitting the EX100-2 with a hydraulic conversion kit is often done to bypass aging electronics or simplify control systems. These kits typically involve rerouting pilot lines, replacing solenoids with manual valves, or modifying the pump control logic. While the concept is straightforward, execution can be fraught with challenges.
One recurring issue involves incorrect hose routing at the pump solenoids. If the two control lines are reversed, the machine may start but bog down under load and only perform a single function—such as boom lift or bucket curl—while ignoring other commands.
Symptoms of incorrect routing:
Understanding Solenoid-Controlled Pump Logic
The EX100-2 uses solenoids mounted on top of the hydraulic pump to regulate swash plate angle and flow output. These solenoids receive electrical signals from the controller based on joystick input. When retrofitting, these solenoids are often bypassed or replaced with manual valves.
Key concepts:
Diagnosing Single-Function Behavior
When an excavator only performs one hydraulic function, the issue often lies in:
Pump Load Sensing and Engine Bogging
Engine bogging during hydraulic operation typically points to excessive load demand or poor flow modulation. In the EX100-2, the pump is load-sensing, meaning it adjusts output based on demand from the control valves. If the load-sensing line is blocked or misrouted, the pump may default to maximum displacement, overwhelming the engine.
Solutions include:
Field Anecdotes and Lessons Learned
A fleet manager in Ireland shared that his EX100-2 retrofit worked flawlessly after he reversed the solenoid hoses and added a manual override valve. He emphasized the importance of tracing each line individually and not relying solely on diagrams, which may vary by region or production year.
Another owner in Canada noted that his machine refused to operate after a conversion until he discovered a blocked pilot line caused by a crushed fitting under the cab floor—damaged during transport.
Conclusion
Retrofitting the hydraulic system on a Hitachi EX100-2 can breathe new life into an aging machine, but it requires careful attention to hose routing, solenoid logic, and pressure feedback. When the machine runs but only performs a single function—or bogs under load—the issue is often a misrouted pilot line or a misinterpreted control signal. With methodical diagnostics and a willingness to trace every connection, operators can restore full functionality and keep this classic excavator working for years to come. The EX100-2 may be decades old, but with the right hydraulic tweaks, it still has plenty of digging left to do.
The Hitachi EX100-2 was part of a pivotal generation of Japanese-built excavators that helped define the global mid-size market in the 1990s. With an operating weight of roughly 10 metric tons and a proven Isuzu diesel engine, the EX100-2 offered a balance of power, reliability, and serviceability. Hitachi Construction Machinery, founded in 1970, had by then become a major player in the earthmoving sector, with the EX series gaining traction across Europe, Asia, and North America.
The EX100-2 featured a hydraulic system built around pilot controls and a variable displacement pump, making it responsive and efficient for trenching, grading, and demolition work. However, as machines aged and parts availability shifted, many owners opted to retrofit or convert the hydraulic system—especially when dealing with solenoid failures or outdated control logic.
Hydraulic Conversion Kits and Common Pitfalls
Retrofitting the EX100-2 with a hydraulic conversion kit is often done to bypass aging electronics or simplify control systems. These kits typically involve rerouting pilot lines, replacing solenoids with manual valves, or modifying the pump control logic. While the concept is straightforward, execution can be fraught with challenges.
One recurring issue involves incorrect hose routing at the pump solenoids. If the two control lines are reversed, the machine may start but bog down under load and only perform a single function—such as boom lift or bucket curl—while ignoring other commands.
Symptoms of incorrect routing:
- Engine bogs when attempting multi-function operation
- Only one hydraulic function responds
- No movement when hoses are connected per diagram
- Machine runs normally when hoses are swapped, but behavior is inconsistent
Understanding Solenoid-Controlled Pump Logic
The EX100-2 uses solenoids mounted on top of the hydraulic pump to regulate swash plate angle and flow output. These solenoids receive electrical signals from the controller based on joystick input. When retrofitting, these solenoids are often bypassed or replaced with manual valves.
Key concepts:
- Swash plate angle determines pump displacement
- Pilot pressure modulates valve spool movement
- Solenoids act as on/off gates for hydraulic signal routing
- Incorrect hose placement can cause the pump to default to low flow or stall under load
Diagnosing Single-Function Behavior
When an excavator only performs one hydraulic function, the issue often lies in:
- Pilot signal routing
- Pressure compensation logic
- Flow priority valve settings
- Internal pump control spool sticking
- Verify hose routing against factory and conversion diagrams
- Check pilot pressure at each control valve using a gauge
- Inspect solenoid connectors for corrosion or voltage drop
- Confirm that the pump control spool moves freely under pilot pressure
Pump Load Sensing and Engine Bogging
Engine bogging during hydraulic operation typically points to excessive load demand or poor flow modulation. In the EX100-2, the pump is load-sensing, meaning it adjusts output based on demand from the control valves. If the load-sensing line is blocked or misrouted, the pump may default to maximum displacement, overwhelming the engine.
Solutions include:
- Installing a pressure relief valve in the pilot circuit
- Verifying load-sensing line continuity and pressure
- Cleaning or replacing the pump control spool
- Adjusting engine throttle linkage for better response
Field Anecdotes and Lessons Learned
A fleet manager in Ireland shared that his EX100-2 retrofit worked flawlessly after he reversed the solenoid hoses and added a manual override valve. He emphasized the importance of tracing each line individually and not relying solely on diagrams, which may vary by region or production year.
Another owner in Canada noted that his machine refused to operate after a conversion until he discovered a blocked pilot line caused by a crushed fitting under the cab floor—damaged during transport.
Conclusion
Retrofitting the hydraulic system on a Hitachi EX100-2 can breathe new life into an aging machine, but it requires careful attention to hose routing, solenoid logic, and pressure feedback. When the machine runs but only performs a single function—or bogs under load—the issue is often a misrouted pilot line or a misinterpreted control signal. With methodical diagnostics and a willingness to trace every connection, operators can restore full functionality and keep this classic excavator working for years to come. The EX100-2 may be decades old, but with the right hydraulic tweaks, it still has plenty of digging left to do.
