TM 55-2815-574-24
0003
AIR INDUCTION SYSTEM - Continued
Blower
The large bearing blower, designed especially for efficient diesel operation, supplies the fresh air needed for
combustion and scavenging. Its operation is similar to that of a gear-type oil pump. Two hollow three-lobe rotors
revolve with very close clearances in a housing bolted to the top deck of the cylinder block, between the two
banks of cylinders. To provide continuous and uniform displacement of air, the rotor lobes are made with a helical
(spiral) form.
The three-piece seals were replaced by double lip teflon oil seals in 1986. Each rotor is supported in the doweled
end plates of the blower housing by a roller bearing at the front end and a double-row radial and thrust ball
bearing at the gear end. The right-hand helix rotor of the blower is driven by the blower driveshaft. The blower
driveshaft is splined at one end to a drive hub attached to the blower drive gear and at the other end to a drive
hub attached to the right-hand helix blower timing gear. The mating left-hand helix timing gear drives the left-hand
helix rotor. Two timing gears, located on the drive end of the rotor shafts, space the rotor lobes with a close
tolerance. Therefore, as the lobes of the two rotors do not touch at any time, no lubrication is required. This timing
must be correct, otherwise the required clearance between the rotor lobes will not be maintained. A change in
rotor timing is obtained by the use of shims between the gears and the bearings.
The blower bearings, timing gears, governor drive and fuel pump drive are pressure lubricated by oil passages in
the top deck of the cylinder block which lead from the main oil galleries to an oil passage in each blower end
plate. A cup shaped oil strainer has been incorporated in the vertical oil passage at the bottom side of each
blower end plate to remove any foreign material in the lubricating oil. The oil flows upward in the end plate and
leaves through a small orifice just above the center line of the end plate. The oil is ejected from this orifice against
the timing gears at the rear and the governor weights at the front of the blower and is then carried by splash to the
bearings. Oil, which collects at the bottom of each end plate, overflows into two drain passages which lead back
to the crankcase via oil passages in the cylinder block. The blower drive support bearings receive oil under
pressure from a tube which connects the oil passage in the rear end plate to passages in the blower drive
support. Excess oil drains back to the crankcase by way of the gear train.
After Cooler
The after cooler mounts in the cylinder block opening between the cylinders, beneath the blower assembly. The
after cooler cools the air going into the engine after it passes through both the turbocharger and the blower. The
air flows downward through the after cooler and the coolant flows from rear to front through the after cooler and
returns through the left bank thermostat housing. The top deck of the cylinder block has been revised to accept
the after cooler. A water inlet adapter plug or cup plug replaces the rear 2-1/2 in. (63.5 mm) core plug in the
bottom of the cylinder block opening to supply water to the after cooler.
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