54 Auto Fundamentals
Overhead Camshaft I-Head
Some I-head engines mount the camshaft in
the head. Either one or two shafts can be used.
When an overhead camshaft is used, push rods
are not required. The rocker arm setup shown
in Figure 3-11 is operated by the camshaft lobe
rubbing directly on the rocker. Zero valve stem-
to-rocker clearance is maintained by a hydraulic
valve lash adjuster, Figure 3-12, which operates
in the same manner as the hydraulic lifter dis-
cussed earlier in Chapter 2, Design, Construction,
and Application of Engine Components. The cam-
shaft lobes can also be arranged to work directly
on the valves as shown in Figure 3-13.
Overhead Valve Adjustment
Some overhead valve installations pro-
vide an adjusting screw in the push rod end of
the rocker arm. This screw is moved in or out
until the recommended clearance is obtained
between the valve stem and the rocker arm. See
Figure 3-14. Some engines use hydraulic lifters,
which eliminates the need to adjust clearance.
The only adjustment necessary is the initial set-
ting to place the lifter plunger at the halfway
point in its travel. Some engines make the initial
setting with adjustable rocker arms, while oth-
ers use push rods that provide the proper set-
ting when installed. Figure 3-15 shows such a
setup. Push rods of slightly different lengths are
available to make minor changes.
Fuel
injector
Hydraulic valve
lash adjuster
Rocker
arm
Block
Piston
Valve
Cam lobe
Camshaft
Figure 3-11.
One type of overhead camshaft rocker arm arrangement.
Note the hydraulic lash adjuster.
Ford Motor Co.
Rocker arm
Camshaft pulley
Hydraulic
lash adjuster
Piston
Valve
Valve spring
Figure 3-12.
Cross-sectional view of an engine that incorporates a single
overhead camshaft (SOHC) to operate the valves. Note the
use of a hydraulic valve lash (clearance) adjuster.
Chrysler
Figure 3-13.
Dual overhead camshaft (DOHC), 16-valve, valve train.
Note the camshaft lobes act directly on the ends of the
valves. No rocker arms are used.
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