This workshop service manual provides comprehensive information for the David Brown AD4-25 and CAD4-30 Diesel Engines. These engines are known for their robust construction and reliable performance, making them suitable for a variety of demanding applications. This manual details the engineering and design principles that contribute to their durability and efficiency, ensuring users can understand and leverage the full capabilities of these power units. The purpose of this manual is to serve as a definitive guide for the maintenance, repair, and servicing of the David Brown AD4-25 and CAD4-30 Diesel Engines. It covers essential procedures, technical specifications, and diagnostic troubleshooting steps. By following the detailed instructions within this document, owners, technicians, and mechanics can effectively maintain the operational integrity and longevity of their engines, ensuring optimal performance and minimizing downtime.