This manual covers the Yanmar 4-6BY Series marine engines, including models 4BY-150/150Z, 4BY-180/180Z, 6BY-220/220Z, and 6BY-260/260Z. These engines are engineered for reliable marine propulsion, embodying Yanmar's commitment to quality and performance in demanding maritime environments. Their robust design and advanced engineering ensure efficient operation and longevity for a wide range of marine applications. The Yanmar 4-6BY Series Service Repair Manual provides comprehensive guidance for maintaining and repairing these marine engines. It details essential procedures for periodic maintenance, engine service, and specific systems such as fuel, cooling, lubrication, and turbocharging. The manual also covers starter motor, alternator, and electrical/ECU service, along with detailed troubleshooting information, empowering owners and technicians to keep their Yanmar engines operating at peak performance.