Hitachi EX120 & EX120-2 Excavator 1986–1994 Technical Manual (P/N T105-01-01-002)

• Built for owners and workshops servicing the 1986–1994 Hitachi EX120 and Hitachi EX120-2 series excavators with Isuzu 4BD1T powerplants
• Official Hitachi technical publication code 105T-01-01, detailing operational principles and hydraulic systems
• Contains 56 individual section drawings, 12 hydraulic flow schematic diagrams, and 8 system-level pressure regulation charts
• Documented maintenance specifications for hydraulic fluid, engine oil, coolant, and gear oil change intervals
• This technical manual provides the operational framework for the 12N serial number range, distinguishing the EX120-2 build from the earlier EX120 iterations
• Breaks down component logic for the accumulator, center joint, swing bearing, travel motor, shockless valve, proportional solenoid valve, and unloading valve
• Features system metrics covering interchangeability, lifting capacities, working ranges, parking brakes, travel reduction devices, pilot pumps, make-up valves, and DP-sensors

Structural and System Documentation

The 1986–1994 Hitachi EX120 service manual documentation covers the primary machine systems through an extensive set of technical diagrams. Initial sections detail the general configuration of the excavator, identifying components of the front-end attachment, upperstructure, and undercarriage. Subsequent chapters outline the principles of the hydraulic systems, including the main pump assembly, pilot device, and control valves. Electrical and mechanical sensing components, such as the N-sensor, P-sensor, and A-sensor, are presented with cross-sectional views and signal flow logic for the controller. Before loosening any pressurized line for a repair, technicians must verify the machine is parked on a level surface, the bucket is grounded, and all hydraulic pressure is fully relieved to prevent severe fluid injection injuries.

Control valves are analyzed in detail, with chapters dedicated to the variable pressure compensated valve (VPCV) for both motor and cylinder circuits. Additional sections explore the operational principles of the surge relief valve, swing dampener valve, and the anti-cavitation functions inherent to the swing device. Documentation concludes with a breakdown of pilot piping, including the warm-up circuit and shuttle valve logic, providing a clear reference for the interplay between the pilot hydraulic lines and the main machine functions. This PDF outlines step-by-step procedures for adjusting the auxiliary spool speed and safely verifying accumulator nitrogen gas levels, allowing independent shops to complete specialized component tests that typically require an expensive dealer service call.

Specifications and Operational Data

Technical specifications are categorized by system to assist with identification and maintenance planning. Fluid capacities are explicitly documented for the hydraulic tank, engine crankcase, and swing/travel reduction gears to ensure correct replenishment. Torque values for system relief and pilot pressure adjustments are listed, supporting the accurate tuning of hydraulic delivery. The cooling system capacity for the 1986–1994 Hitachi EX120 is 16.4 liters. Track shoe width for the 1986–1994 Hitachi EX120 is listed at 500 mm as a standard configuration. Hydraulic suction filter maintenance is described as being required during every major hydraulic oil replacement cycle. By translating sensor signal logic into traceable diagnostic paths, technicians can accurately evaluate differential pressure outputs and isolate flow restrictions during troubleshooting, avoiding the trial-and-error replacement of expensive main pumps.

An official 451-page Hitachi technical manual (P/N 105T-01-01) covering the 1986–1994 Hitachi EX120 and EX120-2, documenting hydraulic operational principles, system layout, and component-level specifications for the 12N-series excavator build.

Isolate complex hydraulic faults and minimize machine downtime with this exact factory specification reference.