This document provides instructions for removing and installing unit injector sleeves and the unit injector hydraulic pump on Caterpillar C9 engines. The procedures include draining coolant, using various tools to cut threads and remove the sleeves, cleaning parts, applying retaining compound, reinstalling sleeves and O-rings, and reconnecting fuel lines and electrical harnesses when installing the pump. Technicians are advised to keep parts clean and contain fluids properly during the process.