This manual covers the Yanmar GM/HM Series Marine Diesel Engines, including models 1GM10, 2GM20, 3GM30, 3HM35, and their 'F' and 'C' variants. These engines are known for their robust construction and reliability, designed for marine applications where dependable power is essential. Whether configured as single, two, or three-cylinder units, and utilizing direct sea-water or fresh-water cooling systems, these engines represent quality engineering for demanding maritime environments. This comprehensive Factory Service/Repair/Workshop Manual provides detailed information essential for the maintenance and repair of your Yanmar marine diesel engine. It includes in-depth coverage of maintenance procedures, repair instructions, diagnostic troubleshooting, and exploded diagrams. Specific sections address the fuel system, lubrication system, electrical system, reduction reversing gear, and remote control system. This manual is an indispensable resource for owners, mechanics, and technicians to ensure the optimal performance and longevity of their Yanmar engines.