This manual covers the Mitsubishi S4S and S6S diesel engines, which are integral components of specific Hyundai Excavator and Fork Lift series. Engineered for robust performance and reliability, these water-cooled engines are designed to meet the demanding operational requirements of heavy machinery. Their application in Hyundai Excavator models (16-18TON, -7 Series) and Hyundai Fork Lift models (HDF35-70, -7 Series) underscores their suitability for industrial and construction environments. The purpose of this comprehensive English Service Repair Manual is to provide detailed information for the maintenance, repair, and troubleshooting of the Mitsubishi S4S/S6S engines. It includes essential sections on general information, engine parts, fuel, lubrication, cooling, inlet/exhaust, and electrical systems, along with procedures for inspection, adjustment, assembly, disassembly, and performance testing. This manual is an indispensable resource for owners, mechanics, and technicians seeking to ensure the optimal performance and longevity of their equipment.