This manual covers the YANMAR 4BY / 6BY Marine Engine, a line of inboard diesel internal combustion engines designed for marine propulsion. These engines feature a V-type cylinder configuration, with the 4BY model utilizing four cylinders and the 6BY model employing six cylinders. Engineered for reliability and performance in demanding marine environments, the YANMAR 4BY / 6BY series represents a robust solution for boat owners and operators seeking dependable power. The YANMAR 4BY / 6BY Marine Engine Factory Service Repair Workshop Manual provides comprehensive guidance for all aspects of engine maintenance and repair. It includes detailed servicing and repair procedures, a dedicated troubleshooting guide, and is enhanced with hundreds of pages featuring detailed photos, diagrams, and exploded views. This manual is an essential resource for owners, mechanics, and technicians, enabling them to effectively maintain, diagnose, and repair the engine, ensuring its optimal performance and longevity.