This manual covers the Yanmar 1GM10, 2GM20, 3GM30, and 3HM35 diesel engines. These engines are known for their robust construction and reliable performance, making them suitable for a variety of marine applications. The Yanmar series offers a range of power outputs, from the 1GM10 with approximately 7.7 kW (10.5 PS) to the 3HM35 with approximately 22.1 kW (30 PS), and varying displacements to suit different vessel requirements. Their engineering prioritizes durability and efficiency, ensuring dependable operation in demanding environments. The purpose of this Service Repair Manual is to provide comprehensive guidance for the maintenance, repair, and technical understanding of these Yanmar engines. It details operating instructions, engine specifications including cooling systems, fuel, intake, exhaust, lubrication, and electrical systems. Furthermore, it covers the reduction and reversing gear transmission, remote control systems, and includes procedures for disassembly and reassembly. This manual is an essential resource for owners, mechanics, and technicians seeking to maintain optimal performance and longevity of their Yanmar engines.