This service repair manual covers the Hyundai Mitsubishi S4S and S6S engines, specifically designed for use in Hyundai Excavator 16 to 18 Ton 7 Series and Hyundai Forklifts HDF35-70 7 Series equipment. These engines are recognized for their robust engineering and reliable performance, making them a cornerstone for demanding industrial applications. This manual provides comprehensive information to ensure these vital components operate at peak efficiency throughout their service life. The purpose of this English-language manual is to serve as an authoritative guide for maintaining and repairing the specified Hyundai Mitsubishi engines. It details critical procedures including disassembly of main engine parts, fuel system, lubrication system, cooling system, inlet and exhaust system, and electrical system overhauls. Furthermore, it includes troubleshooting procedures, assembly instructions, wiring diagrams, electrical and hydraulic diagrams, schemes, and step-by-step operations with real photo illustrations, empowering owners, mechanics, and technicians with the knowledge needed for effective service.