This repair manual covers Volvo Penta marine engines, specifically models 230, 250, 251-DOHC, AQ131, AQ151, and AQ171. These internal combustion DOHC engines are engineered for reliable marine performance. This comprehensive guide is designed to assist users in maintaining and repairing these robust marine powerplants, ensuring their continued operational efficiency and longevity on the water. The purpose of this English-language repair manual is to provide detailed instructions for routine maintenance, advanced troubleshooting, and component lookup. It covers essential areas such as lubrication and cooling systems, fuel systems, intake and exhaust, electrical systems, transmission, drive chains and sprockets, steering systems, engine removal and installation, and body work. Technical specifications and procedures for shocks are also included, offering a complete resource for owners and technicians to effectively manage and service their Volvo Penta marine engines.