The components that transmit the power—the pistons, con- necting rods and crankshaft— are hidden inside the cylinder block, and the outside of the block and cylinder head car- ries a number of vital ancillary components.

These include the inlet and exhaust manifolds, which carry fuel and air to the cylinders and pipe exhaust gas out, carburet- tor, distributor, starter motor, generator and usually the pet- rol pump. The positions of these components vary a little depending on the layout of the engine. The drawing shows where they are located on four- cylinder engines found on the majority of small cars.

Some of the outside corn po- nents are hard to find. The carburettor is usually beneath a big air filter, and the exhaust manifold may be half buried in a heat box that directs warm air to the carburettor.

In addition, there will be a number of small diameter hoses. Besides taking water to and from the interior heater, hoses often feed water from the cylinder block to a jacket round the inlet manifold, where warmth helps to vaporise the mixture. They also pipe crank- case fumes to the in let manifold.

The heavy metal

Because substantial tempera- tures and forces are generated within an internal combustion engine, the components in direct contact with these loads must be extremely rigid and very strong to withstand the demands made upon them. There are three major assemblies:

The cylinder head contains the combustion chambers, the valves—there are usually two to each cylinder—the springs that close the valves and the valve gear that opens them and the inlet and exhaust ports.

The cylinder block contains the cylinders and houses the crankshaft, pistons and connecting rods.

It may also carry the cam- shaft, but on some engines this is mounted above the cylinder head, and where this is done, the engine is known as an over- head camshaft (OHO) engine.

In water-cooled engines, both the cylinder block and cylinder head contain pas- sages through which cooling water circulates. The crankshaft assembly includes the pistons, connect- ing rods and the crankshaft. The shaft is carried in main bearings mounted between the cylinders at the bottom of the cylinder block.

At one end of the crankshaft is the flywheel.

At the base of the engine a pressed steel or cast aluminium sump provides a reservoir for lubricating oil. At the top, a cover keeps in the oil that lubricates the valve gear and, on modern engines, pro- vides a seal against atmospheric air.