This service repair workshop manual covers the YANMAR 4BY-150 and 4BY-180 marine diesel engines. These robust 4-cylinder internal combustion engines are designed for marine propulsion, offering reliable performance with power outputs of 150 HP and 180 HP respectively. Engineered for demanding marine environments, these YANMAR engines are built to deliver consistent power and efficiency for a wide range of watercraft. This comprehensive manual provides detailed, step-by-step instructions for all repairs, servicing, and troubleshooting procedures. It includes hundreds of detailed photos, diagrams, and exploded views to assist owners, mechanics, and technicians in maintaining and repairing their YANMAR engines. The manual is designed to offer full coverage without limitations, ensuring that all aspects of engine maintenance and repair are thoroughly addressed.