This manual covers the YANMAR 4BY/6BY Marine Engine, an internal combustion engine designed for marine propulsion. These engines are engineered for reliability and performance, offering robust solutions for various marine applications. This comprehensive workshop repair manual provides in-depth information to ensure optimal operation and longevity of your marine propulsion system. The purpose of this manual is to provide detailed guidance for all aspects of service, repair, and maintenance for the YANMAR 4BY/6BY Marine Engine. It includes routine maintenance procedures, troubleshooting, technical specifications, and step-by-step repair instructions, supplemented with clear diagrams and wiring schematics. This resource is invaluable for owners and technicians seeking to understand, maintain, and repair their engines efficiently, potentially saving significant costs on professional services.