This manual covers the Yanmar 6SY Series Marine Diesel Engine, specifically models 6SY720 and 6SY655. Designed for marine propulsion, these engines represent Yanmar's commitment to engineering quality and reliability. The 6SY Series is built to deliver robust performance and dependable operation in demanding marine environments, ensuring efficient power for a wide range of vessels. This English-language Operation Manual provides comprehensive guidance for the Yanmar 6SY Series Marine Diesel Engine. It details essential information regarding operation, maintenance, inspection, handling precautions, and periodic maintenance procedures. The manual also includes guidance on long-term storage. This resource is designed to assist owners, technicians, and mechanics in ensuring the optimal performance, longevity, and safe operation of their Yanmar marine diesel engines.