The YANMAR JH4 Series Marine Diesel Engine, encompassing models 3JH4E, 4JH4AE, 4JH4-TE, and 4JH4-HTE, represents a robust and reliable solution for marine propulsion. Engineered for durability and performance, these diesel engines offer a range of power outputs from 27.6 kW to 55.2 kW, suitable for various vessel types. Their design emphasizes efficient operation, utilizing direct injection fuel systems and water-cooled indirect cooling with heat exchangers to ensure optimal thermal management. The series includes naturally aspirated, turbocharged, and turbocharged and intercooled variants, providing flexibility for different operational demands. This Service Shop Repair Manual provides comprehensive guidance for the maintenance and repair of the YANMAR JH4 Series Marine Diesel Engines. It covers essential procedures including lubrication, filter replacement, and impeller servicing, detailing recommended intervals and capacities. Technical specifications, such as engine displacement and power output, are clearly outlined for each model. Furthermore, the manual offers insights into troubleshooting and repair, equipping owners, mechanics, and technicians with the necessary information to ensure the continued optimal performance and longevity of their YANMAR marine diesel engines.