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Monday, October 22, 2012

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.
Marine Engineering – Third Class – Study Guide and Training Manual
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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.

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