This repair manual covers Yanmar marine diesel engines, specifically models 3JH4E, 4JH4AE, 4JH4-TE, and 4JH4-HTE. These internal combustion engines are engineered for reliable performance in marine applications. This manual provides comprehensive guidance for the repair and maintenance of all versions of these specified models, ensuring optimal functionality and longevity for your vessel's power plant. The purpose of this manual is to serve as a definitive resource for owners, technicians, and mechanics. It details essential maintenance procedures, including routine servicing, engine removal and installation, and specific system upkeep for fuel, lubrication, cooling, transmission, steering, and electrical systems. Furthermore, it offers advanced troubleshooting guidance and technical specifications, empowering users to effectively maintain and repair their Yanmar marine engines.