This manual covers the Yanmar 4BY-150, 4BY-180, 6BY-220, and 6BY-260 marine engines. These internal combustion diesel engines are engineered for reliable marine propulsion, offering robust performance across various applications. Their design emphasizes durability and efficiency, making them a trusted choice for demanding maritime environments. The purpose of this English-language service repair manual is to provide comprehensive guidance for the maintenance and repair of your Yanmar marine engine. It details essential procedures, technical specifications, and troubleshooting steps to ensure optimal performance and longevity. By following the instructions within this manual, owners and technicians can effectively maintain and service these engines.