This manual covers the David Brown AD4-25 Diesel Engine, a robust and reliable power unit designed for demanding applications. Engineered for durability and efficient operation, the AD4-25 is known for its consistent performance and straightforward design, making it a trusted choice for various industrial and agricultural uses. Its construction emphasizes longevity and ease of maintenance, ensuring dependable service throughout its operational life. The purpose of this comprehensive workshop service manual is to provide detailed information for the maintenance, repair, and troubleshooting of the David Brown AD4-25 Diesel Engine. It includes essential technical specifications, step-by-step repair procedures, diagnostic guidance, and safety precautions. This manual serves as an indispensable resource for owners, technicians, and mechanics, enabling them to effectively maintain the engine's optimal performance and longevity.