This workshop service manual covers the YANMAR BY Series engines, including the 4BY and 6BY models. These engines are engineered for robust performance and reliability, featuring in-line diesel configurations with turbocharging and water-cooling systems. The 4BY models are 1.995L four-cylinder engines, while the 6BY models offer a larger 2.993L displacement in a six-cylinder configuration. Designed for demanding applications, these engines represent a commitment to durable and efficient power. This comprehensive English-language manual provides detailed, step-by-step instructions, accompanied by pictures and diagrams, to assist both do-it-yourself owners and experienced mechanics. It covers a wide range of essential topics, including general maintenance, engine systems, fuel and cooling systems, electrical components, and troubleshooting. The manual is designed to facilitate the proper upkeep and repair of your YANMAR BY Series engine, ensuring its continued optimal operation.