This manual covers the Komatsu 4D98, 4D106, and S4D106 series engines, also cross-referenced with Yanmar models 4TNE94, 4TNE98, 4TNE106, and 4TNE106T. These 4-cylinder internal combustion engines are designed for a variety of applications requiring reliable power. The series includes naturally aspirated and turbocharged variants, with displacement varying by specific model. This shop manual provides comprehensive information for the repair, overhaul, and fault finding of these robust Komatsu engines. The purpose of this English-language shop manual is to guide owners, mechanics, and technicians through the maintenance and repair processes. It details all necessary specifications and tolerances, explains component functions, and offers step-by-step instructions for correct and efficient repairs, aiming to save time and avoid errors. The manual features high-quality diagrams, pictures, and illustrations to facilitate understanding and ensure accurate execution of all procedures.