Cylinder Block: The casting that comprises the main structure of an IC (Internal Combustion) engine. The cylinder block is the connecting unit for the cylinder heads, crankshaft, and external assemblies, plus it houses the pistons, camshaft and all other internal engine components. The stability, strength, and precision of the block casting and machining are extremely important in obtaining optimum power and engine life. Cylinder blocks are usually made from a high grade of cast iron.