This manual covers GM 4 Cylinder In-Line marine engines, specifically those with displacements ranging from 2.5L to 3.0L (153-181 cid), produced between 1985 and 1989. It details models such as MCM 120 MR, MCM 120 Alpha I, MCM 2.5L, MCM 140 MR, MCM 140 Alpha I, MCM 3.0L, and Sea Ray 3.0L, along with their respective serial number ranges. These engines are designed for marine applications, utilizing driveshaft extension models like MR and Alpha I. This comprehensive Service and Repair manual in English provides essential information for maintaining and repairing your engine. It includes detailed maintenance procedures, troubleshooting guides, assembly and disassembly instructions, and wiring diagrams for fuel, cooling and exhaust, electrical, power steering, and engine mechanical systems. The manual is designed for all operating systems, requiring only a PDF reader, and all pages are printable for your convenience.