This manual covers Westerbeke Universal marine engines, including models M-12, M2-12, M3-20, M4-30, M-18, M-25, M-25XP, and M-35. Westerbeke has been a leader in marine power since 1898, and these engines are engineered for reliability and performance in marine applications. This document provides comprehensive information for the maintenance, service, diagnosis, and repair of these essential marine power units. The purpose of this factory service/repair/workshop manual is to provide detailed guidance for all aspects of Westerbeke Universal marine engine upkeep. It includes specifications, preventive maintenance schedules, in-depth explanations of construction and function, and detailed procedures for lubrication, cooling, and fuel systems. Furthermore, the manual covers the electrical system, dynamo and regulator, disassembly and reassembly, and troubleshooting, offering step-by-step instructions with highly detailed exploded pictures and diagrams to ensure accurate and efficient service.