1986-1994 Hitachi EX120 & EX120-2 Excavator Technical Manual

Technical Scope and Coverage for the 1986–1994 Hitachi EX120 & EX120-2

• 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
• Downloads to your account within seconds of checkout
• Indexed PDF search covers every chapter and appendix
• 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.

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.

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.

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.

An official 451-page Hitachi technical manual 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.

Document Reference: 105T-01-01