This workshop repair manual covers the YANMAR 4BY 150 and 4BY 180 marine engines. These 4-cylinder diesel internal combustion engines are engineered for marine propulsion, offering robust performance and reliability. The YANMAR brand is recognized for its commitment to quality, ensuring these engines are built to withstand the demanding conditions of marine environments. This manual provides comprehensive information for owners and technicians alike. The purpose of this English-language manual is to offer detailed guidance on the maintenance and repair of your YANMAR marine engine. It encompasses all areas of repair, routine maintenance, and servicing jobs, presented with step-by-step instructions and accompanying pictures. Included are essential wiring diagrams to aid in diagnostics and repairs. This resource is designed to help you effectively maintain and service your engine, ensuring its optimal performance and longevity.