This workshop repair manual covers Mercury Mercruiser #4 MCM sterndrive engines, model range 120-260. These inboard/outboard (I/O) engines are known for their robust engineering and reliable performance in marine applications. The MCM series, encompassing models from 120 to 260 horsepower, offers a versatile power solution for a variety of watercraft. This manual provides comprehensive information to ensure the optimal operation and longevity of your Mercruiser propulsion system. The purpose of this English-language manual is to serve as a definitive guide for owners, technicians, and mechanics. It details essential maintenance procedures, troubleshooting techniques, and repair instructions for critical components including the drive unit, transom plate assembly, power trim, and power steering systems. Included are general information sections, diagnostic procedures, and important service bulletins, all designed to facilitate efficient and accurate upkeep of your Mercruiser engine.