This manual covers the Yanmar 4BY and 6BY marine diesel engines, designed for reliable marine propulsion. These engines represent a commitment to robust engineering and performance, ensuring efficient operation for a variety of marine applications. Their construction prioritizes durability and longevity, making them a trusted choice for demanding maritime environments. The purpose of this service repair manual is to provide comprehensive guidance for the maintenance and repair of your Yanmar marine diesel engine. It details essential procedures for engine systems, fuel, cooling, lubrication, turbocharger, starter motor, alternator, and electrical systems. This manual is an indispensable resource for owners, mechanics, and technicians, offering the necessary information to ensure optimal performance, longevity, and safe operation of the Yanmar 4BY and 6BY series engines.