MAIN COMPONENTS OF A PISTON ENGINE

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Engines may vary considerably but the majority incorporate the components listed

below.

Engine Construction.

1. Cylinder block and crankcase. The unit forms the principal part of the

engine. It may be cast as a single unit, or the cylinders may be detachable from

the crankcase.

2. Cylinder head. The head, usually detachable, is bolted to the cylinder block

and forms a gas tight and water tight ‘lid’ on each cylinder.

3. Sump. This is a light casing fitted to the underside of the crankcase to

contain the lubricating oil.

4. Piston. The piston is a sliding fit in the cylinder bore. It is fitted with piston

rings to prevent gas leakage past the piston. The top of the piston is known as

the crown. The lower part, which acts as the guide is called the piston skirt.

5. Connecting rod. The connecting rod is attached to the piston at one end by a

gudgeon pin which is fitted to the piston. This is known as the Little End. The

bottom end of the connecting rod is attached to the crankshaft, at the Big End

Bearing.

6. Crankshaft. The crankshaft is carried in main bearings which are part of the

crankcase casting. It converts the reciprocating movement of the piston to

more useful rotary movement.

7. Flywheel. Most internal combustion piston engines have a heavy flywheel to

carry the engine over the non-power strokes, particularly in the four-stroke

engine where there is only one power stroke in four on each piston. The

flywheel is attached to the crankshaft, and is outside the crankcase.

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8. Valves. The valves are usually fitted in the cylinder head, and are called

overhead valves. When open they allow the passage of Air, Fuel, and Exhaust

gas, when shut they seal the cylinder.

9. Camshaft. Each valve is lifted by a cam, which is pear shaped and machined

in an angular position on the camshaft so that it will lift the valve for the

correct period.

10. Rocker gear. Overhead valves are operated by rockers with one end of each

rocker bearing on the cam or push rod, and the other end on the valve stem.