The YANMAR 3YM20 is a robust marine diesel engine designed for reliable performance in maritime applications. This naturally aspirated, 3-cylinder engine displaces 1.266 liters and delivers 20 horsepower (14.7 kW). It offers both direct freshwater and raw water cooling options, ensuring efficient operation across various marine environments. Engineered for durability and consistent power output, the 3YM20 is a trusted choice for boat owners and operators seeking dependable propulsion. This Full Service Repair Manual provides comprehensive guidance for the YANMAR 3YM20 marine diesel engine. It covers essential maintenance procedures, including oil and filter changes, as well as detailed diagnostic, rebuilding, refurbishing, and restoration procedures. The manual includes technical specifications, troubleshooting guides, and detailed illustrations, drawings, and wiring diagrams to assist owners, mechanics, and technicians in maintaining and repairing the engine. This English language manual is designed to facilitate proper upkeep and ensure the longevity of your YANMAR 3YM20.