Engine Block

The engine block is the main structural component of an engine. It supports and helps maintain alignment of internal and external components. The engine block consists of a cylinder block and a crankcase. An engine block can be produced as a one-piece or two-piece unit. The cylinder block is the engine component that consists of the cylinder bore, cooling fins on air-cooled engines, and valve train components, depending on the engine design. The cylinder bore is a hole in an engine block that aligns and directs the piston during movement. The bore of an engine is the diameter of the cylinder bore. The stroke of an engine is the linear distance that a piston travels in the cylinder bore from top dead center (TDC) to bottom dead center (BDC).

Top Dead Center (TDC) is the point at which the piston is closest to the cylinder head. Bottom Dead Center (BDC) is the point at which the piston is farthest from the cylinder head. Displacement (swept volume) is the volume that a piston displaces in an engine when it travels from TDC to BDC during the same piston stroke. Generally, the larger the displacement of the engine, the more power it can produce.

An air-cooled cylinder block has cooling fins on the exterior. A cooling fin is an integral thin cast strip designed to provide efficient air circulation and dissipation of heat away from the engine cylinder block into the air stream. Fins or vanes increase the surface area of the cylinder block contacting ambient air for cooling efficiency. Cooling fins cast into or bolted onto the flywheel act as fan blades to provide air circulation around the cylinder block and head. Air circulation dissipates heat generated during combustion to maintain optimum engine temperatures. A crankcase is an engine component that houses and supports the crankshaft. In a four-stroke cycle engine, the crankcase also acts as an oil reservoir for lubrication of engine components. The crankcase may be a part of the engine block or a separate component.