This document is a workshop manual providing instructions for servicing and repairing Perkins 3012/CV12 12 cylinder diesel engines. It includes specifications, instructions for removing and installing various engine components, and procedures for inspecting, testing, dismantling, and assembling those components. The manual covers the cylinder head assembly, pistons and connecting rods, crankshaft assembly, timing gears, crankcase, camshafts, induction and exhaust systems, and lubrication system.