Long blocks are fully assembled engine short blocks, complete with cylinder heads, valve trains, and often the intake and exhaust manifolds. These units replace a severely damaged engine block while retaining ancillary components like the fuel system and wiring harness. Critical features include pre-installed camshafts, valve springs, and rocker arms, ensuring proper valve timing and lift. Long blocks are utilized in a broad range of vehicle applications, offering a cost-effective alternative to a complete engine replacement. They require technicians to transfer existing components, verifying compatibility and proper sealing during installation.