COMPONENTS OF THE ENGINE

ENGINE BLOCK

The engine block is the main body of the engine; all parts of the engine are either inside the engine block or attached to the outside of it. The engine block is a one-piece casting of iron, but actually it is considered in two parts, the crankcase and the cylinder block.

1. Crankcase

To illustrate the two parts of the engine block, an imaginary box has been drawn around the lower portion of the engine block. This lower portion is known as the crankcase. 

FOUR CYLINDER ENGINE BLOCK (LEFT VIEW)

The crankcase, which supports the crankshaft, is hollow inside with one or more rib-like castings that form the main frame.

EIGHT CYLINDER ENGINE BLOCK

2. Cylinder Block

The upper portion of the engine block is the cylinder block. This portion contains the cylinders, the water passages commonly known as the "water jacket"  and oil passages. 

ENGINE BLOCK COOLANT FLOW

OIL PASSAGES

The cylinders are individual housings for the pistons. They are large holes cast into the cylinder block, extending completely through it. The walls of the cylinders are machined smooth to reduce the friction generated by the moving parts inside of them. Some engines have cylinder liners inserted into the cylinder opening. The water jacket, a large passage cast into the cylinder block, surrounds the cylinders. It contains water or a commercial coolant to maintain a safe temperature while the engine is operating. Note the oil passages. The oil passages provide a way to distribute oil under pressure to all moving parts of the engine to reduce wear and to aid the water jacket in cooling the moving parts.

In most cases, the cylinder block contains a camshaft, and, in some cases it contains the valves. Image shows the top of the cylinder block. In addition to the cylinders, several smaller holes are cut into the surface. Other holes are cut into the water jacket and into the oil passages. The surface of the cylinder block top is machined smooth and must be perfectly flat.

CYLINDER BLOCK AND WATER JACKET