This manual covers Volvo Penta diesel marine engines, specifically the MD21A, MD32A, AQD21A, and AQD32A models from 1975. These engines are known for their robust diesel power and reliability in marine applications. The MD21A and AQD21A models feature 2.1-liter, 4-cylinder configurations, while the MD32A and AQD32A models offer 3.2-liter, 6-cylinder powerplants. Both raw water and freshwater cooling systems were available, depending on the specific configuration. These engines are designed for demanding marine use, providing dependable propulsion. This Service Repair Manual provides comprehensive guidance for the maintenance and repair of your Volvo Penta marine diesel engines. It includes detailed information on routine maintenance procedures, such as recommended oil change intervals and fuel type specifications. The manual also offers valuable troubleshooting assistance and step-by-step overhaul instructions, supported by exploded view illustrations to aid in identification and assembly. This resource is essential for owners, mechanics, and technicians seeking to ensure the optimal performance and longevity of these engines.