This operation manual covers the Yanmar 4BY and 6BY marine diesel engines, designed for reliable marine propulsion. These engines represent robust engineering, built to provide dependable performance in demanding marine environments. Their diesel fuel type ensures efficient operation, making them a suitable choice for various marine applications requiring consistent power output. This manual provides comprehensive guidance for the operation and maintenance of your Yanmar marine diesel engine. It includes essential information on engine operation, periodic maintenance procedures, troubleshooting, and long-term storage. Detailed specifications and safety guidelines are also provided to assist owners and technicians in ensuring the longevity and optimal performance of the Yanmar 4BY and 6BY models.