This repair manual covers Yanmar GM/HM Series marine diesel engines, including models 1GM, 1GM10, 2GM, 2GM20, 2GM20F, 2GMF, 3GM, 3GM30, 3GM30F, 3GMD, 3GMF, 3HM, 3HM35, 3HM35F, and 3HMF. These engines are designed for marine applications and feature 1, 2, and 3-cylinder configurations. The Yanmar brand is known for its engineering quality and reliability, making these engines a trusted choice for various boating needs. This comprehensive guide ensures you have all the necessary information to maintain and operate your Yanmar marine diesel engine effectively. The purpose of this English-language repair manual is to provide detailed instructions for performing repairs, identifying parts, and conducting routine maintenance on the specified Yanmar marine diesel engines. It covers a wide range of topics, including general information, routine maintenance, engine removal and installation, fuel systems, lubrication and cooling systems, engine specifications, transmission, drive chains and sprockets, steering systems, shocks, body work, intake and exhaust systems, electrical systems, and advanced troubleshooting. This manual is an essential resource for owners, mechanics, and technicians seeking to ensure the optimal performance and longevity of their Yanmar engines.