This service repair manual covers the Yanmar 2QM20(H) and 3QM30(H) marine diesel engines. These engines are designed for marine propulsion, featuring a water-cooled, direct injection internal combustion system. The 2QM20(H) is a 2-cylinder engine with 0.855 L displacement, producing 20 HP at 2800 RPM, while the 3QM30(H) is a 3-cylinder engine with 1.283 L displacement, producing 30 HP at 2800 RPM. These engines are engineered for reliability and performance in marine applications. This manual provides comprehensive guidance for the maintenance and repair of your Yanmar marine diesel engine. It includes detailed procedures for servicing, recommended oil types such as SAE 10W-30 API CD, and oil capacities for both models. Owners, mechanics, and technicians will find essential information on troubleshooting, technical specifications, and safety guidelines to ensure optimal engine performance and longevity. Refer to this manual for recommended service intervals and other critical operational details.