This service manual covers Hyundai and Mitsubishi LPG Gas Forklift Trucks, specifically models HLF 15-5, HLF 18-5, HLF 20-5, HLF 25-5, and HLF 30-5, equipped with the 4G63 and 4G64 engine families. These engines, including variants such as 4G63-32HL, 4G64-33H, 4G63, and 4G64, are known for their robust construction and reliable performance in demanding industrial environments. This manual provides comprehensive technical information designed to ensure the continued operational efficiency and longevity of these vital material handling machines. The purpose of this English-language service and repair manual is to provide detailed instructions and specifications for the maintenance, diagnosis, and repair of the 4G63/4G64 LPG gas engines. It includes essential information on general engine specifications, torque values, sealant applications, required tools, and step-by-step procedures for all major engine components. Furthermore, this manual offers troubleshooting guidance to help identify and resolve common issues, making it an indispensable resource for owners, technicians, and mechanics seeking to maintain these Hyundai and Mitsubishi forklift trucks.