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TM 9-8000
f. Crankshaft Main Bearings (Fig. 3-44). The upper
halves of the main bearings fit right into the crankcase,
and the lower halves fit into the caps that hold the
crankshaft in place. The main bearings have holes drilled
in their upper halves through which a supply of oil is fed
to them. The crankshaft has holes drilled in the journals
that receive oil from the main bearings to feed the rod
bearings. It is a common practice to cut a groove In the
center of the main bearing Inserts. This supplies a more
constant supply of oil to the connecting rod bearings.
One of the main bear- Ings also serves as a thrust
bearing. This controls back and forth movement of the
crankshaft. This thrust bearing Is characterized by side
3-11. Flywheel(Fig.3-45).
a. General. The flywheel stores energy from the power
strokes, and smoothly delivers it to the drive train of the
vehicle. It mounts on the end of the crankshaft, between
the engine and the transmission.
b. Manual Transmission. When the vehicle Is equipped
with a manual transmission, the fly- wheel serves to
mount the clutch.
Figure 3-36. Crankshaft Counterweights.
c. Automatic Transmission. When the vehicle Is
equipped with an automatic transmission, the flywheel
(3) Antiscuffing.  The  bearing  surface should be
serves to support the front of the torque converter. On
able to absorb enough oil to keep It from scuffing during
some configurations, the flywheel is combined with the
startup, or any other time when It must run momentarily
torque converter.
without an oil supply.
d. Starter Ring Gear. The outer edge of the flywheel Is
(4) Embedabillty. The surface of the bearing must be
lined with gear teeth. They are to engage the drive gear
soft enough to allow particles of foreign matter to embed
on the starter motor.
themselves and prevent damage of the shaft journal.
e. Construction. The flywheel on large, low- speed
(5) Conformability. The bearing must be able to
engines usually Is made of cast iron. This Is desirable
conform or fit itself to the surface of the crankshaft
due to the heavy weight of the cast Iron, which helps the
engine maintain a steady speed. Small, high-speed
(6) Conductivity. The bearings must be able to
engines usually use a forged steel or forged aluminum
flywheel for the following reasons.
conduct heat to the connecting rod so that they will not
(1) The cast iron is too heavy, giving it too much
(7) Resistance to Heat. The bearing must be able to
inertia to allow the speed variations necessary on small
maintain all of these characteristics throughout its entire
operating temperature range.
(2) Cast iron, because of its weight, will pull itself apart
at high speeds due to centrifugal force.
e. Connecting Rod Lubrication (Fig. 3-43). The
connecting rod bearings fit into the lower end of the
connecting rod. They are fed a constant supply of oil
through a hole In the crankshaft Journal. A hole In the
upper bearing half feeds a passage In the connecting rod
to provide oil to the piston pin.


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