This service repair manual covers Mercury MerCruiser marine engines, specifically the GM 4 Cylinder family, including the 2.5L (153 CID) and 3.0L (181 CID) models. These engines are known for their robust design and reliable performance in marine applications. The manual details various series such as MCM 120 MR, MCM 120 ALPHA I, MCM 140 MR, MCM 140 ALPHA I, MCM 2.5L, MCM 3.0L, and SEA RAY 3.0L, applicable to specific serial number ranges. This comprehensive guide provides essential information for maintaining and repairing your Mercury MerCruiser engine. It includes detailed procedures for engine mechanical work, removal and installation, driveshaft extensions, and covers critical systems like starting, ignition, charging, fuel delivery, exhaust manifolds, and power steering. With step-by-step instructions, exploded views, pictures, and diagrams, this manual is an indispensable resource for owners and technicians to ensure optimal engine performance and longevity.