Lesson 1/Learning Event 1
Engine Block
The engine block, sometimes called the cylinder block, serves as the foundation for, and houses most of, the
other engine parts. The block contains the cylinder which can be compared to the bore of a gun. The cylinder
is perfectly round and machined to a smooth finish. The lower end of the engine block is flared out to form
the upper half of a cavity for housing other parts. The lower half of the cavity is enclosed on the bottom by a
separate housing or pan, commonly called the oil pan. The entire cavity is called the crankcase.
Piston
Fitted into the cylinder is a movable piston that receives the energy or the force from the combustion of the
fuel-air mixture. The piston is comparable to the bullet of the gun. The top of the piston, called the piston
head, is closed. The lower part, or skirt, of the piston is open and fits in the cylinder very tightly. This
prevents the piston from tipping or slapping about in the cylinder. The upper part of the piston has grooves to
accept metal rings. A hole is machined just below the ring grooves so the piston can be pinned to a rod.
Piston Rings
Although it's a small amount, there must be some clearance between the piston skirt and the cylinder wall so
the piston can slide freely. Piston rings are placed in the piston ring grooves to prevent gases from leaking
through this operating clearance. The metal piston rings are not a solid band but are cut through in one spot.
This way, the cut ends can be spread apart and the ring passed over the piston to place it in the ring groove.
The split ends (ring gap) do not form a perfect seal, so more than one ring is used, and the joints are staggered
to reduce leakage.
Cylinder Head
The top end of the cylinder is closed with a cylinder head that is secured to the engine block with several bolts.
The space between the cylinder head and the piston forms a chamber for the combustion of the fuel-air
mixture. To prevent leakage, a metal or metal-asbestos cylinder head gasket is placed between the head and the
block. A spark plug for igniting the fuel-air mixture is screwed into a threaded hole in the top of the head that
extends into the combustion chamber.
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