Mazda Training manual - part 232

 
2 – BASIC OPERATION 

 

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Piston Engine Fundamentals

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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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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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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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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.