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 marine propulsion, offering robust performance and durability for a wide range of watercraft. Their design emphasizes efficiency and longevity, making them a trusted choice for maritime applications where dependable power is essential. This comprehensive workshop repair and service manual provides detailed information for maintaining and repairing your YANMAR marine diesel engine. It includes general information, specifications, lubrication details, periodic maintenance procedures, engine servicing, disassembly and reassembly instructions, and troubleshooting guidance. With numerous illustrations and diagrams, this manual is an indispensable resource for owners, mechanics, and technicians to ensure optimal performance and longevity of the engine.