This manual covers Yanmar GM Series and HM Series diesel inboard engines, specifically the 1, 2, and 3-cylinder models, produced between 1980 and 2009. These engines, including generations like the 1GM, 2GM, and 3GM series, are known for their robust construction and reliability in marine applications. Designed for dependable performance, these Yanmar engines offer efficient power for a variety of vessels, emphasizing enduring quality and operational excellence. This comprehensive shop manual provides essential information for the operation, maintenance, and repair of your Yanmar engine. It details general information, troubleshooting procedures for common issues such as starting, charging, fuel, cooling, and exhaust problems, as well as lubrication, maintenance schedules, tune-up procedures, and layup instructions. The manual also includes specific guidance on fuel injection, cooling, electrical systems, and the KM and KBW series transmissions, along with wiring diagrams, ensuring that owners and technicians have the resources needed to keep these engines running optimally.