This manual covers the Yanmar 1GM10(C), 2GM20(F)(C), 3GM30(F)(C), and 3HM35(F)(C) marine diesel engines, designed for reliable marine propulsion. These engines are engineered for robust performance and durability in demanding marine environments. The models incorporate single, twin, and three-cylinder configurations, with specific designations indicating Compact versions (C) and Freshwater cooling systems (F), ensuring adaptability for various vessel requirements. This comprehensive repair, service, and shop manual provides essential information for maintaining and troubleshooting your Yanmar marine diesel engine. It details general information, routine maintenance procedures, engine removal and installation, fuel system, lubrication and cooling systems, and transmission. Additionally, it includes advanced troubleshooting guides and technical specifications, empowering owners and technicians to ensure optimal engine performance and longevity.