This service repair manual covers Mercury Mercruiser #3 Marine Engines produced between 1978 and 1984. These robust engines, based on GM engine blocks with Mercury Marine additions and marinization, are available in Inline 4-Cylinder, Inline 6-Cylinder, and V-8 Cylinder configurations. The manual details a wide array of specific engine models, including MCM 120, MCM 140, MCM 165, MCM 470, MCM 485, MCM 898, MCM 228, MCM 260, MCM 330, MCM 400 Cyclone, MCM 440 Cyclone, MCM 460 Cyclone, and various Turbo models, alongside their associated Velvet Drive and Mercury Marine transmissions. It also addresses different cooling systems, fuel systems including various carburetor types, exhaust components, and drive systems. This comprehensive English-language manual provides essential information for the maintenance and repair of your Mercury Mercruiser engine. It includes detailed tear-down and rebuild procedures, maintenance schedules, troubleshooting guides for common issues, torque specifications, and complete wiring schematics. With over 1000 pages of step-by-step instructions, part diagrams, and detailed illustrations, this manual is an indispensable resource for owners, mechanics, and technicians seeking to ensure the optimal performance and longevity of their marine engines. The manual is searchable, bookmarked, and printable, offering convenient access to critical technical data.