This manual covers the YANMAR YM Series marine engines, including the 3YM30, 3YM20, 2YM15, and 3YM models. These engines are designed as vertical, water-cooled, 4-cycle, naturally aspirated diesel units, offering reliable performance for marine applications. The YM Series is engineered for durability and efficiency, providing a robust power solution for various vessel types. This comprehensive workshop and operating manual provides essential repair and service information for YANMAR YM Series engines. It details maintenance procedures, troubleshooting guides, and technical specifications, including engine types and displacements for specific models. The manual is designed to assist both DIY enthusiasts and professional mechanics in maintaining the optimal performance and longevity of these marine engines.