This manual covers the YANMAR 3YM30, 3YM20, and 2YM15 marine diesel engines. These engines are engineered for reliability and performance in marine applications, featuring vertical, water-cooled, 4-cycle configurations with naturally aspirated aspiration. The 3YM30 boasts a displacement of 1.115 liters, the 3YM20 offers 0.854 liters, and the 2YM15 has a displacement of 0.570 liters. Their robust construction and efficient design make them suitable for a wide range of marine vessels. This comprehensive Workshop Service & Repair Manual, along with an included Operating Manual, provides detailed technical information essential for maintaining and repairing your YANMAR engine. It covers a broad spectrum of topics, including general information, engine components, fuel and lubrication systems, cooling, electrical systems, and troubleshooting. With step-by-step instructions, detailed illustrations, and diagrams, this manual is an invaluable resource for do-it-yourself owners and experienced mechanics alike, ensuring optimal performance and longevity of your marine diesel engine.