Figure 3-53. Driving the Camshaft.

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Figure 3-51. Valve Rotators.

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TM-9-8000 Principles of Automotive Vehicles Manual

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Figure 3-55. Mechanical Tappets.

TM 9-8000

Figure 3-53. Driving the Camshaft.

crankshaft must rotate twice as fast as the camshaft, the

camshaft to operate the pump. On diesel engines, the

drive member on the crankshaft must be exactly one-half

camshaft often Is utilized to operate the fuel Injection

as large as the driven member on the camshaft. In order

system.

for the camshaft and crankshaft to work together, they

h. Tappets. Tappets (or lifters) are used to link the

must be In the proper Initial relation to each other. This

camshaft to the valve mechanism. The bottom surface Is

Initial position between the two shafts Is designated by

hardened and machined to be compatible with the

marks that are called timing marks. To obtain the

surface of the camshaft lobe. The following are the two

correct Initial relationship of the components,

the

basic lifter classifications:

corresponding

marks

are aligned at the time of

(1)Mechanical Tappets (Fig. 3-55). Mechanical (or

assembly.

solid) lifters are simply barrel-shaped pieces of metal.

g. Auxiliary Camshaft Functions (Fig. 3-54).

When used In flathead engines, they have an adjusting

The camshaft, after being driven by the crank-shaft, In

screw mechanism to set the clearance between the

turn drives other engine components. On gasoline

tappets and the valve stems. Mechanical tappets may

engines, the oil pump and the distributor usually are

also come with a wider bottom surface. These are called

mushroom tappets. Another variation Is the roller tappet,

driven from a common gear that Is machined Into the

which has a roller contacting the camshaft. They are

camshaft. The fuel pump Is also driven by the camshaft.

used mostly In heavy-duty applications to reduce

This usually Is accomplished by machining an extra lobe

component wear.

the

(2)Hydraulic Tappets (Fig. 3-56). The hydraulic tappet

Is very popular In overhead valve engines. It uses oil

under pressure to automatIcally maintain zero clearance

In the valve mechanism. The lifter body, which contacts

the camshaft lobe, Is hollow. Inside the lifter body, there

Is a plunger that operates the valve mechanism. Injecting

oil into the cavity under the

TA233381

Figure 3-54. Auxiliary Camshaft Functions.

3-31