This manual covers the Westerbeke M12--M35 Series marine engines, designed for marine power generation. This series includes models such as the M-12, M2-12, M3-20, M4-30, M-18, M25, M25XP, and M35. These engines are engineered for reliability and performance in demanding marine environments, providing consistent power output for various onboard systems. The Westerbeke M12--M35 Series Factory Service Manual provides comprehensive guidance for maintenance, service, diagnosis, and repair. It includes detailed information on specifications, preventive maintenance, construction and function, lubrication, cooling, fuel systems, electrical systems, disassembly and reassembly, the dynamo and regulator, and troubleshooting. With step-by-step instructions and detailed diagrams, this manual is an essential resource for owners and technicians to ensure the optimal performance and longevity of their Westerbeke marine engines.