CRANKSHAFT, MAIN BEARINGS, FLYWHEEL & CRANKCASE
The crankshaft is fully counterbalanced and the journals
are induction hardened. The D and DT-466 engines are
also fillet hardened. There are seven main bearings,
with the number - 7 (rear) bearing absorbing the end
thrust. The crankshaft extension at the foreward end
carries the main drive gear, a splined collar (which drives
the lubricating oil pump) and the vibration damper. The
gear and splined collar are a shrink fit and the damper, a
press fit. The damper hole is keyed to the shaft and held
in place by a retainer plate. The flywheel is mounted to
the rear end of the crankshaft. Two seals, one at the
front and one at the rear, prevent leakage of engine
lubricating oil around the ends of the crankshaft.
Bearing caps are furnished with the crankcase and these
support the crankshaft in true alignment. Webs integral
with the crankcase provide the upper half of the main
bearing supports and removable caps provide the lower
support. The caps are held in place with cap screws.
The bearing caps are NOT interchangeable, and each
has a number stamped upon it which signifies its correct
location in the crankcase, as shown in Fig. 3. Number 1
is at the front of the engine.
Figure 3. - Bearing Cap (Top View) Identification
The flywheel Is attached to the rear of the crankshaft. Its
purpose is to oppose and moderate by its inertia any
fluctuations in the speed of the engine. It counteracts
variable torques during the stroke of the engine, and
provides a rotating balance weight that carries the engine
crankshaft over dead centers on the pistons.
It is secured to the end of the crankshaft with bolts. The
cranking motor drive ring gear is a shrink fit and is
There are two basic crankcases used: one for the 300
Series and one for the 400 Series Engines. The main
differences are the physical dimensions; the 400 Series
case is longer and higher.
All crankcases have seven main bearing areas with the
thrust bearing saddle located at the rear. All cases are
line bored with the caps in place and the bolts tightened
to the specified torque. All caps are marked and are not
interchangeable within the case itself or with other cases.
On Turbocharged engines, each main bearing web has
angled-drilled holes, which are fitted with coolant jet
tubes that direct lubricating oil, under pressure, to the
underside of each piston. A percentage of the lubricating
oil fed to the main bearings passes through milled slots
in the upper half of the bearing shells. The stream of oil
from these jets is a constant flow during all periods of
engine operation. N.A. engine crankcases have the
twelve oil-jet holes plugged with balls.
There are two oil galleries cast into the case; one
handles unfiltered oil from the pump to the cooler and
then from the cooler to the filter base. Oil leaving the
filter enters the second gallery and is distributed to
various points of lubrication throughout the engine. Both
galleries are sealed at the front and rear of the case with
plugs. The camshaft is located directly above these
galleries and is supported on finished bushings pressed
into the case.
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