This Service Repair Workshop Manual covers Komatsu diesel engines from the 110 Series, specifically models equipped with the S6D110-1 and SA6D110-1 engines. These engines are integral to various Komatsu equipment, including the WA350-1, EG150-3, EG150S-3, D66S-1, W120-2, W120-3, WA380-1, WA400-1, WA420-1, and EC210Z-1. This manual is designed for serial numbers 10001 and up, providing comprehensive technical information for these robust and reliable machines. The purpose of this manual is to serve as a definitive guide for the maintenance, repair, and technical understanding of the specified Komatsu engines. It details engine structure and function across various systems, including intake and exhaust, engine body, lubrication, fuel, cooling, and electrical systems. Furthermore, it provides essential troubleshooting guidance, maintenance standards for inspection, and step-by-step procedures for parts replacement, including specific components like valve seat inserts and crankshaft gears. Engine performance curves and weight tables are also included to support in-depth analysis and service.