This service repair workshop manual covers Yanmar marine diesel engines, including models 1GM10, 2GM20, 3GM30, 3HM35, and their 'F' and 'C' variants. These engines are engineered for reliable marine propulsion, offering robust performance for a variety of maritime applications. The manual is designed to provide comprehensive information for maintaining and repairing these essential marine power units, ensuring their continued operational efficiency and longevity. The scope of this English-language manual is extensive, detailing procedures for general maintenance, basic engine overhauls, and specific systems such as fuel, governor, intake, exhaust, lubrication, and both direct sea-water and fresh-water cooling systems. It includes instructions for reduction and reversing gears, remote control systems, and electrical components, alongside disassembly and reassembly guides. With hundreds of photos, illustrations, and step-by-step instructions, this manual serves as an indispensable resource for both do-it-yourself owners and experienced mechanics seeking to understand and service their Yanmar marine diesel engines.