This manual covers the Westerbeke 20B TWO and 30B THREE marine diesel engines. These 4-cycle, water-cooled engines are designed for marine propulsion. The 20B TWO features a 0.635L 2-cylinder vertical configuration, while the 30B THREE offers a 0.952L 3-cylinder vertical setup. Both models utilize a fuel injection pump and injection nozzle system, a glow plug and starter system for ignition, and an alternator system for charging. Westerbeke engines are engineered for reliability and performance in demanding marine environments. This comprehensive Service Repair Manual, Operator Manual, and Parts Catalogue provides detailed information to ensure proper operation and maintenance of your Westerbeke engine. It includes step-by-step procedures for engine overhaul, disassembly, and specific component repairs such as the cylinder head, gearcase, timing gears, piston, connecting rod, and governor system. The manual also contains troubleshooting guides, technical specifications including tightening torques, and exploded views with diagrams and pictures. This resource is essential for owners, mechanics, and technicians seeking to maintain, repair, and optimize the performance of their Westerbeke 20B TWO or 30B THREE marine diesel engines.