This service manual covers the John Deere 120 Excavator. Engineered for demanding work, the John Deere 120 Excavator is recognized for its robust construction and reliable performance, making it a valuable asset for various excavation tasks. Its design prioritizes efficiency and durability, ensuring consistent operation in challenging environments. This comprehensive manual provides detailed guidance for operating, maintaining, diagnosing, and repairing the John Deere 120 Excavator. It includes essential information such as general specifications, safety precautions, fuel and lubricant recommendations, and operational checkout procedures. Furthermore, it delves into the intricacies of the engine, electrical system, power train, and hydraulic system, offering theory of operation, diagnostic information, adjustments, and test procedures to assist owners and technicians in keeping the equipment in optimal condition.