Chapter 5 Fundamentals of Engine Construction and Operation 89
elsewhere in the engine compartment. Some oil filters are
installed in the oil pan or an engine-mounted canister and
do not have housings.
Oil Galleries
Oil galleries are internal engine passages that carry
the oil. They are cast or drilled into the engine block and
heads. Galleries extend from the pump and filter to the
crankshaft and camshaft bearings, valve lifters, and rocker
arm shafts. Galleries are drilled in the crankshaft to allow
oil to reach the connecting rod bearings. Removable plugs
are located at the rear of some engine blocks to allow the
galleries to be cleaned during an overhaul.
Gaskets, Seals, and Sealant
Gaskets and seals are used in the intake system to seal
air and fuel in and to prevent vacuum leaks. Preventing
fuel and air leaks is vital to driveability, performance, and
emissions. Gaskets and seals must stand up to high engine
temperatures, but be pliable enough at various operating
temperatures to create the intended seal.
Summary
The four-stroke cycle operates through two revolu-
tions of the crankshaft. The intake stroke draws air and fuel
into the cylinder. The compression stroke compresses the
air-fuel mixture. When the mixture ignites, it pushes the
piston down for the power stroke. On the exhaust stroke,
the upward movement of the piston pushes the exhaust
gases out of the cylinder. The cycle then repeats.
The major components of a reciprocating-piston
engine are the engine block, pistons and rings, connecting
rods, crankshaft, cylinder head(s), valves, and valve train.
The valves are driven by the crankshaft through a set of
gears, a gear and chain arrangement, or sprockets and a
drive belt. On some engines, valve operation is controlled
by a mechanism operated by a computer.
The cooling system removes unwanted engine heat
and regulates engine temperature. Cars and light trucks
have a liquid cooling system. Coolant is pumped through
engine passages by a belt-driven pump. A radiator removes
heat from the coolant. Engine coolant is a mixture of anti-
freeze and water. Antifreeze may be ethylene glycol or
propylene glycol.
Poor lubrication can eventually result in driveability
symptoms. The lubrication system circulates engine oil to
internal engine parts. Oil galleries are internal passages that
carry the oil throughout the engine. The oil pump is driven
by a gear on the camshaft or by the engine timing belt. A
pressure regulator controls oil pump output. The engine oil
provides lubrication, reduces friction, helps with cooling,
seals, provides shock absorption between parts, and cleans
parts. It is formulated to prevent sludge formation.
Review Questions—Chapter 5
Please do not write in this text. Write your answers on
a separate sheet of paper.
1. Name the four strokes in a four-stroke cycle engine.
2. List the major parts installed on or in the engine
block.
3. The ______ transfer the force of the expanding
combustion gases to the connecting rods.
4. A film of ______ between the compression rings and
cylinder wall seals pressure in the cylinder.
(A) carbon
(B) oil
(C) unburned fuel
(D) None of the above.
5. The _____ converts the straight-line motion of the
piston into rotary motion.
(A) piston
(B) crankshaft
(C) flywheel
(D) connecting rod
6. What holds intake and exhaust valves closed?
(A) The camshaft.
(B) Compression pressure.
(C) Valve spring pressure.
(D) Expanding combustion gases.
Figure 5-29. Oil filters come in many sizes and shapes. While it
is a very simple and inexpensive part, the filter is very important
to good engine performance.