Mazda Training manual — part 232

2 – BASIC OPERATION

13

Piston Engine Fundamentals

TC010-05-01S

Refer to the illustration below to complete the following two items.

4. This illustration shows the _____________________ stroke of the four-stroke cycle.
5. Item “ ” in the illustration is the ________________________.

BASIC DESIGN CHARACTERISTICS

There are many variations in basic engine design, and automotive technology has its own
vocabulary for describing these designs. Engines are often described by the various
arrangements and measurements of their components, including:

• Cylinder

configuration

• Valve train type

• Size of the engine’s bore, stroke, and displacement

• Compression

ratio

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Piston Engine Fundamentals

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FIGURE 6. A
four-cylinder
in-line engine
has four
cylinders
arranged in a
single row.

Cylinders

FIGURE 7. A V-6
engine has two
banks of three
cylinders
arranged in a
“ V” pattern

Cylinders

Cylinder Configuration

Automotive engines typically have four, six, or eight cylinders, which are
arranged either in a line or in a “V” shape. Figure 6 shows the typical
arrangement of a
4-cylinder in-line engine. As the illustration shows, the cylinders are all in
one straight row. Most 4-cylinder engines are built with the cylinders in-line.














Figure 7 shows another typical cylinder arrangement, the V-6 engine. The
V-6 has two banks of three cylinders arranged in a “V” pattern. Even though
the cylinders are in two banks, they are still connected to a common
crankshaft.

















The V-8 engine is a variation of this design. The V-8 includes two banks of
four cylinders each, arranged in a “V” pattern.

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Piston Engine Fundamentals

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Valve Train Type

Mazda engines have the valves mounted above the cylinders in the
cylinder head. The valves are operated by a camshaft, which controls the
opening and closing of the valves. An overhead valve, or OHV design, has
the camshaft installed below the valves, in the engine block. If the
camshaft is mounted above the cylinders, the design is called overhead
cam,

or OHC.

In some engines, a single camshaft is used to operate both the intake and
exhaust valves. In many engines, though, a dual overhead camshaft
(DOHC)

design is used. The DOHC design uses one camshaft to operate

the intake valves, and the other camshaft to operate the exhaust valves.
This arrangement eliminates extra weight, allowing the engine to operate
at higher RPMs. Figure 8 shows a DOHC design in a 4-cylinder in-line
engine.

Answers to
Review Exercise

1. cylinder

2. crankshaft

3 flywheel

4. power

5. spark

plug

FIGURE 8 The dual
overhead camshaft
(DOHC) design uses
sepa- rate camshafts
for the intake and
exhaust valves. Two
camshafts are used
on this 4-cylinder
in-line engine

Intake camshaft

Intake valve

Exhaust camshaft

Exhaust valve

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Piston Engine Fundamentals

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FIGURE 9. A V-6
or V-8 DOHC
engine has two
sets of
camshafts, one
for each bank of
cylinders. A total
of four
camshafts are
used on this V-6
engine.

Exhaust
camshaft,
right bank

Intake
camshaft,
right bank

Intake
camshaft,
left bank

Exhaust
camshaft,
left bank

A V-6 or V-8 DOHC engine will have two sets of camshafts, one set for
each bank of cylinders. Figure 9 shows the two sets of camshafts on a V-6
engine.