This manual covers the Yanmar QM, GM-HM, 4JH & 4JH2 Series marine diesel engines and transmissions manufactured between 1975 and 1992. These robust internal combustion engines and transmission systems are engineered for reliable marine applications, offering dependable performance for a variety of watercraft. This comprehensive workshop service repair manual provides detailed information to ensure the continued optimal operation of your Yanmar marine propulsion system. The purpose of this English-language manual is to provide owners, mechanics, and technicians with all necessary information for the maintenance and repair of the specified Yanmar engines and transmissions. It includes A-Z repair and service procedures, presented with easy-to-follow, step-by-step instructions and accompanying visuals. By utilizing this guide, users can confidently perform their own servicing and repairs, contributing to cost savings and extended equipment life.