This Service and Repair Manual covers Komatsu Diesel Engines, specifically the 3D82AE, 3D84E, 3D88E, 4D88E, 4D98E, 4D106, S4D84E, S4D98E, and S4D106 series. These engines are integral to a range of heavy equipment, including excavators, wheeled excavators, and log loaders. Komatsu engines are engineered for robust performance and reliability in demanding operational environments, ensuring consistent power and efficiency for critical tasks. This manual provides comprehensive documentation for these diesel engines, supporting their continued optimal function. This manual serves as an essential resource for maintaining and repairing the specified Komatsu diesel engines. It details a wide array of procedures, including general information, inspection and adjustment, troubleshooting, and in-depth disassembly, inspection, and reassembly of engine components. Coverage extends to critical systems such as lubrication, cooling, and fuel injection, as well as the turbocharger, starting motor, and alternator. Technical specifications, service standards, tightening torques, and various diagrams, including wiring, electrical, and hydraulic diagrams, are also provided. The manual is presented in English and features searchable text and bookmarked sections for ease of use by owners, mechanics, and technicians.