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Part of the Hitachi Repair Manuals.
Need the factory answer for your Hitachi EX120 hydraulic excavator? All 984 pages of this Hitachi EX120 service manual PDF dig into the real machine: hydraulic pump device, control valve, swing device, travel device, undercarriage, and a full engine section. You get complete wiring diagrams, hydraulic schematics with full circuit routing, exploded views for every major assembly, and a heavy troubleshooting section built for chasing real faults. Set pilot valve primary pressure at 40 kgf/cm2 (3900 kPa) and confirm the solenoid relief valve cracks above 38 kgf/cm2 (3700 kPa) before you blame the pump. No more diagnosing a dead swing circuit with a gauge and a guess. Bookmarked with a live text layer; pull it up on your tablet, search the spec, and get wrenching.
What's Inside This Hitachi EX120 Manual
| System | Pages | Key Topics |
|---|---|---|
| How to Use | 1-11 | Section & Group Contents, Introduction, This Manual, Safety Informations |
| Specifications | 12-41 | General Specifications, Components Specifications, Torque References, Others, Conversion Table |
| General | 42-85 | Introduction, Hydraulic System, Electric System, Maintenance |
| Superstructure | 86-391 | Hydraulic Pump Device, Control Valve, Swing Device, Pilot Valve, Mode Selection Cylinder |
| Undercarriage | 392-541 | Travel Device, Center Joint |
| Front-End Attachment | 542-589 | Hydraulic Cylinder, Pin & Bushing, Point & Side Cutter |
| Hydraulic System | 590-641 | Main Hydraulic Circuit, Pilot Circuit, Single Operation, Combined Operation, Extra Control Circuit, Hydraulic Circuit |
| Electrical System | 642-703 | Safety Precautions, Specifications, Construction & Function, Circuit Operations, Maintenance |
| Troubleshooting | 704-812 | Introduction, Diagnose Malfunctions, Excavator Performance Test, Components Performance Standard, Electrical System Test |
| Engine | 813-984 | General Information, Maintenance, Engine Disassembly, Inspection & Repair, Engine Assembly, Lubricating System, Cooling System, Fuel System, Turbo Charger, Engine Electricals, Troubleshooting, Special Tool List |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Engine weight (4BD1T) | 340 kg | p. 822 |
| Engine oil capacity | 13 L | p. 822 |
| Coolant capacity (Engine only) | 8.5 L | p. 822 |
| Valve clearance (Inlet/Exhaust) | 0.4 mm | p. 20 |
| Injection pressure | 185 kgf/cm2 | p. 20 |
| Pilot pump rated pressure | 40 kgf/cm2 | p. 23 |
| Swing motor output torque | 389 N.m | p. 24 |
| Travel reduction device lubrication oil capacity | 3.5 L | p. 410 |
| Track link tightening torque | 45 kgf.m | p. 454 |
| Battery capacity | 65AH x 2 | p. 19 |
Hitachi EX120 Common Problems This Manual Covers
Hitachi EX120 stalls and dies the moment hydraulic control lever is engaged
Check voltage at the brake solenoid valve with the key on; you should read 28V per the diagnostic chart on page 751. Test the DC 24V coil for continuity and inspect harness connectors for corrosion or shorted pins. Replace the solenoid if it fails to actuate anywhere in the 23V to 32V operating range.
Manual Section: Electric System Malfunctions p. 751Hydraulic system won't build pressure and travel feels weak on both tracks
Test pump control pressure at full lever stroke; the EX120 spec is 6.1±0.5 kg/cm², listed on page 717. Verify main pump pressure rises to relief at 325 kg/cm² and the pilot pump holds 40 kgf/cm². If control pressure fails to drop to normal, inspect the pump regulator before pulling the pump.
Manual Section: Hydraulic System MalfunctionsNo swing motion or swing feels weak and jerky through full rotation
Measure pilot valve primary pressure; you need 40 kgf/cm² (3900 kPa) to stroke the swing spool, spec on page 26. Check oil level in the 150 liter hydraulic tank, then inspect the make-up circuit that prevents swing motor cavitation, covered on page 51. Replace the pilot filter element and torque it to 2 to 5 kgf.m.
Manual Section: Hydraulic System MalfunctionsEngine cranks but won't start, or starter motor turns over slowly in cold weather
Verify both 65AH batteries pass a load test before condemning the starter; clean and tighten cable connections while you are there. Confirm fuel reaches the injection pump, bleed the system, and drain any water from the fuel filter. If cranking sounds healthy but it still won't fire, check valve clearance at 0.4 mm cold.
Manual Section: Engine Hard StartingEngine lacks power under load with black smoke when digging or traveling
Inspect the air cleaner element first; a clogged filter starves the turbo and kills power fast. Check valve clearance and reset inlet and exhaust to 0.4 mm per the spec table on page 20. Test injection nozzles at 185 kgf/cm2 opening pressure and rule out a restricted fuel filter before blaming the injection pump.
Manual Section: Engine Insufficient Power p. 20Frequently Asked Questions
How do I adjust the Hitachi EX120 auto-idle speed?
To adjust the auto-idle speed, first loosen the auto-idle lever adjuster bolt. Then, turn the throttle lever to FULL, ensuring the governor lever contacts the stopper L. Finally, adjust the clearance between the top of the mini cylinder and the adjuster bolt using a thickness gauge. For the EX120, the auto-idle cylinder clearance (CA mm) should be 1.0 mm and the E mode cylinder clearance (CE mm) should be 4.0 mm. p. 703
What are the torque specifications for the Hitachi EX120 pump displacement solenoids?
The manual provides a torque specification for the screw used during the assembly of the solenoid valve, which controls pump displacement. When installing screw (20) during solenoid valve assembly, apply locktight and tighten to a torque of 3 kg.m (21.70 ft.lbs). p. 386
What does the Hitachi EX120 error code indicate if the pump swash plate is stuck?
The manual does not specify an error code for a stuck pump swash plate. However, the troubleshooting section for 'Front speed is slow' indicates that if the 'Pump swash plate does not tilt to maximum angle unless SC pressure is less than 10 kgf/cm2', it is a diagnostic condition that needs to be addressed. p. 717
How do I reset the Hitachi EX120 hydraulic pressure after solenoid repair?
The manual does not describe a specific 'reset' procedure for hydraulic pressure after solenoid repair. However, if pressure issues arise, adjustment procedures for various relief valves are detailed. For instance, the pilot relief valve can be adjusted by adding or removing shims to increase or decrease the pressure setting, as outlined on page 780. p. 780
What are the replacement specifications for the Solenoid (brake/hydraulic actuation) on the Hitachi EX120?
The manual provides general specifications for the solenoid valve used in hydraulic actuation. The solenoid valve is identified as model DV-04-H3, operates at DC 24V, and has a weight of 4 kg. p. 28
What do I get after purchasing this Hitachi EX120 manual?
Instant PDF download. You get the full 984-page searchable Service Manual immediately after payment. Open it on your laptop, tablet, or phone right in the shop.
Can I print this manual?
Zero restrictions. The PDF is DRM-free. Print whatever sections you need to take out to the shop. Standard letter or A4 paper works.
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