Page 151 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 135

Figure 2.108 Cam drive belt in position on the Duratec engine; not to be confused with the
serpentine alternator drive belt. (Source: Ford Media)

Figure 2.109 Two types of cam belt

For many engines, a toothed belt is used to drive the camshaft ( Fig. 2.108 ). The
belt is manufactured from a durable, synthetic rubber with reinforcing fi bres. The
teeth moulded on the inside of the belt mate with the corresponding teeth on
the crankshaft and camshaft pulley wheels. The teeth formed on the belt can be
trapezoidal or rounded ( Fig. 2.109 ). Note that they are not interchangeable and it
is important to fi t the correct type when replacing the belt.
Correct tension of the timing belt is imperative for maximum belt life. The belt is
generally tensioned by adjustable tensioner wheels ( Fig. 2.110 ). It is important to
note that manufacturer- and engine-specifi c information must be sought when Key fact
making adjustments in service. The advantages of timing belts are that they are The advantages of timing belts are
cheap and run quietly. that they are cheap and run quietly.
Drive gears ( Fig. 2.111 ) are not used on many applications but have the
advantage of a very positive drive because they have little backlash compared
with belts and chains ( Fig. 2.112 ).
Covers are fi tted to enclose moving parts and retain oil ( Fig. 2.113 ). The sump
or oil pan is fi tted on the underside and holds the oil capacity. The cover that