This manual covers the Yanmar 4BY-150, 4BY-150Z, 4BY-180, 4BY-180Z, 6BY-220, 6BY-220Z, 6BY-260, and 6BY-260Z marine diesel engines. These engines, designed for marine propulsion, are engineered for reliability and performance, offering horsepower ranges from 150 HP to 260 HP. This highly detailed factory service repair manual provides comprehensive guidance for maintaining and repairing these powerful diesel engines, ensuring optimal operation for both do-it-yourself enthusiasts and experienced mechanics. The purpose of this English-language service repair workshop manual is to provide essential information for the upkeep and repair of your Yanmar marine diesel engine. It includes detailed sections on safety, general service information, periodic maintenance, and in-depth procedures for the engine, fuel system, cooling system, lubrication, turbocharger, starter motor, alternator, and electrical systems, including ECU. Troubleshooting guidance is also provided to help diagnose and resolve common issues, ensuring your engine remains in peak condition.