This manual covers the David Brown AD4 25 Engine, a robust and reliable power unit designed for demanding applications. Engineered with precision and built for durability, the AD4 25 Engine is known for its efficient performance and straightforward operation. Its construction emphasizes longevity, making it a trusted choice for various industrial and agricultural uses where consistent power delivery is paramount. The purpose of this workshop service manual is to provide comprehensive guidance for the maintenance, repair, and troubleshooting of the David Brown AD4 25 Engine. It details essential procedures, technical specifications, and diagnostic information necessary for technicians to ensure optimal performance and extend the service life of the engine. Owners and mechanics will find this manual an indispensable resource for understanding the engine's systems and performing necessary upkeep.