This manual covers the Yanmar 1GM10 C, 2GM20 F C, 3GM30 F C, and 3HM35 F C marine diesel engines. These engines are engineered for reliable propulsion in a variety of marine vessels. Their robust design and diesel power deliver dependable performance for boating enthusiasts and professionals alike. This comprehensive document serves as a Repair Manual, Owner's Manual, and Parts Catalog. It details routine maintenance, engine specifications, fuel and lubrication systems, electrical systems, and advanced troubleshooting. This manual is designed to assist owners, mechanics, and technicians in effectively maintaining, repairing, and understanding their Yanmar marine diesel engines.