prevents proper sealing. These seals come in many
LABYRINTH SEALS.-- Labyrinth seals
different shapes and sizes and are not reusable.
contains series of knifelike, soft metal edges that
It is important to use the proper seal (identified
ride very close to a steel surface. A certain amount
by correct part number) for the specific installa-
tion. NEVER use a seal, packing, or O-ring
the steel surface and soft metal edges prevent oil
because they look alike. A seal designed to have
leakage between sections. These seals were used
excellent sealing characteristics in one environ-
as main bearing seals in earlier engines. These seals
ment could be hazardous when used in another.
are made of very soft metal and used at main bear-
Some seals swell when contacted with MIL-L-7808
ing areas. Small nicks in the seal can cause major
oil, while others deteriorate completely.
oil leaks and premature engine changes.
CARBON SEALS.-- Carbon seals are used to
ENGINE OIL SYSTEM DESCRIPTION
contain the oil in the bearing areas. Carbon seals
form a sealing surface by having a smooth carbon
The engine oil system shown in figure 5-14 is
seal rub against a smooth steel surface (faceplate).
a representative engine of a self-contained,
All carbon seals are preloaded. Preloading means
pressurized, recirculating, dry-sump system. It
the carbon seal is held against the steel surface.
consists of the following systems and parts:
Three common methods of preloading carbon
seals are spring tension, centrifugal force, and air
2. Oil pressure and scavenge pump
Figure 5-14.-Engine oil system schematic.