This manual covers the 3JH3E, 3JH3BE, 3JH3CE, 4JH3E, 4JH3BE, and 4JH3CE marine diesel engines. These engines are designed for reliable marine propulsion, offering efficient operation and robust performance for a variety of maritime applications. The JH3 Series is recognized for its engineering quality and durability, ensuring dependable power for your vessel. This comprehensive repair, service, and shop manual provides essential information for maintaining and repairing your marine engine. It details general information, routine maintenance procedures, engine removal and installation, fuel systems, lubrication and cooling systems, engine specifications, transmission, drive chains, sprockets, steering systems, shocks, body work, intake and exhaust systems, and electrical systems. Advanced troubleshooting guidance is also included to assist owners and technicians in diagnosing and resolving issues effectively.