b. Inspection. The blower may be inspected for
any of the following conditions without being removed
from the engine. However, the air inlet silencer must be
removed. Refer to higher echelon if inspection indicates
(1) The air silencer is attached to the air
that blower repair is required.
intake side of the blower rotor housing. A perforated
sheet metal partition divides the silencer into two
sections. The inner portion forms an air duct the entire
length of the silencer. Air enters this duct from both ends
When inspecting a blower on an engine with the engine
and flows toward the outlet opening at the center and
running, keep fingers and clothing away from the moving
then into the blower. The outer portion is filled with
parts of the blower and run the engine at low speeds
sound absorbent, flameproof, felted-cotton waste.
(2) An air intake (blower) screen is used
between the air silencer and the blower housing to
(1) Dirt or chips drawn through the blower will
prevent foreign objects from entering the blower.
make deep scratches in the rotors and housing and
throw up burrs around such abrasions. If burrs cause
(1) Remove the bolt that retains the breather
interference between the rotors or between the rotors
pipe to the air silencer.
and the housing, the blower should be removed from the
(2) While supporting the silencer, remove the
engine and the parts dressed down to eliminate the
six attaching bolts and washers. Then remove the
interference, or the rotors must be replaced if they are
silencer and air intake screen from the blower.
too badly scored.
c. Cleaning. Clean or replace the air intake screen
(2) Leaky oil seals are usually manifested by
the presence of oil on the blower end plates and rotors or
the inside surfaces of the housing. This condition may
d. Installation. Install the screen and silencer in
be checked by running the engine at low speed and
reverse order of removal.
directing a light into the rotor compartment at the end
plates and the oil seals. A thin film of oil radiating away
from the seals is indicative of an oil leak.
a. General. The blower supplies the fresh air
needed for combustion and scavenging. Its operation is
similar to that of a gear-type oil pump. Two hollow three-
Stop engine prior to grasping the top rotor and attempt to
lobe rotors revolve with very close clearances in a
housing bolted to the cylinder block. To provide
continuous and uniform displacement of air, the rotor
(3) A worn blower drive, resulting in a rattling
lobes are made with a helical (spiral) form.
noise inside the blower, may be detected by grasping the
top rotor firmly and attempting to rotate it. Rotors may
move from 3/8 inch to 5/8 inch, measured at the lobe
crown, with a springing action. When released, the
rotors should move back at least 1/4 inch. If the rotors
cannot be moved as directed above, or if the rotors move
too freely, the flexible blower drive coupling should be
inspected and replaced if necessary.
(4) Loose rotor shafts or damaged bearings
will cause rubbing and scoring between the crowns of the
rotor lobes and the mating rotor roots, between the rotors
and the end plates, or between the rotors and the
housing. Generally, a combination of these conditions
exists. A loose shaft usually causes rubbing between the
rotors and the end plates. Worn or damaged bearings
will cause rubbing between the mating rotor
Figure 4-32. Blower air inlet silencer assembly.