members. Two basic types of oil seals used on vehicles
today are synthetic rubber seals and wick seals. Each is
SYNTHETIC RUBBER SEALS. The
synthetic rubber seal (fig. 3-20) is the most common
type of oil seal. It is composed of a metal case used to
retain its shape and maintain rigidity. A rubber element
is bonded to the case, providing a sealing lip or lips
against the rotating shaft. Different types of oil seal
designs are shown in figure 3-20. A coil spring,
sometimes called a garter spring, is used to hold the
rubber element around the shaft with a controlled force.
This allows the seal to conform to minor shaft runout.
Some synthetic rubber seals fit into bores mounted
around the shaft This type is generally a split design
and does not require a metal case or garter spring.
Figure 3-20 shows the effects of pressure on lip seals.
The internal pressure developed during operations
forces the sealing lips tighter against the rotating shaft.
This type of seal only operates effectively against fluid
pressure from one direction. Leather also is used as a lip
seal. In this configuration, the inside diameter of the
seal is smaller than the shaft As the shaft is installed,
the seal bows outward to form a lip seal.
Figure 3-19.Typical gaskets.
WICK SEALS. The wick seal (fig. 3-21) is
made of graphite-impregnated asbestos. Wicking is
sometimes used to control oil leakage. This seal
conforms to the recess in which it is installed. When
using this type of seal, use a knurl finish on the rotating
shaft. The oil is contained between the knurls and seal,
which rub together. As the shaft rotates, the oil is driven
back by the propeller effect of the seal and knurl finish.
An oil slinger sometimes is used with wick seals. The
oil slinger is a raised washerlike area on the shaft. As oil
meets the slinger, it is propelled outward by centrifugal
force. A catch trough then is used to collect the oil and
return it to the sump.
As you gain experience in the mechanical field, you
will be able to recognize the different types of seals and
how they work to prevent leaks. Other types of seals are
discussed in a later module.
MOVING PARTS OF AN
The moving parts of an engine serve an important
functionturning heat energy into mechanical energy.
They further convert reciprocal motion into rotary