TM 5-3895-359-14&P
ENGINE BALANCE AND BALANCE WEIGHTS
Both rotating and reciprocating forces are completely
balanced in the engines. The eccentric rotating masses
of the crankshaft and connecting rods are balanced by
counterweights on the crankshaft cheeks.
The reciprocating masses (the piston and upper end of
the rod) produce an unbalanced couple by virtue of an
arrangement on the crankshaft in which reciprocating
masses, though equal, are not opposite.
This
unbalanced couple, which tends to rock the engine from
end to end, is balanced by an arrangement of rotating
counterweights, mounted at the front and rear ends of
the camshaft and balance shaft, which produce a couple
equal and opposite in magnitude. Consequently the
engine will operate smoothly and in balance throughout
Fig. 2. Loosening Nut on Camshaft or Balance
its entire speed range.
Shaft.
Each set of weights (weights on one shaft comprise a
Remove Front Balance Weights
set) rotates in an opposite direction with respect to the
other. When the two weights at either end of the engine
1. Remove the balance weight cover.
are in a vertical plane, their centrifugal forces are in the
same direction and oppose the unbalanced couple;
2. Place a block of wood between the balance weights
when they are in a horizontal plane, the centrifugal
to prevent rotation (Fig. 2).
forces of these balance weights are opposite and are
therefore canceled. The front balance weights are
3. Loosen the balance weight retaining nuts on the
eccentric in a direction opposite to the rear balance
camshaft and balance shaft with a 1-1/2 " socket wrench
weights. Therefore, rotation will result in the desired
and remove the nuts and internal tooth lock washers.
couple effective only in a vertical plane.
4. Force the balance weight off the end of each shaft
The balance weights consist of two eccentric weights at
with two heavy screw drivers or pry bars between the
each end of the engine and additional weights attached
heads of the bearing retaining bolts and the balance
to the gears.
weight (Fig. 3).
The front balance weights are keyed to the front end of
the camshaft and the balance shaft (Fig. 1).
Current balance weights are of one-piece construction.
Formerly, spring-loaded balance weights were used.
The balance weight bushing oscillates on the hardened
surface if the hub during engine operation. Torque
variations are transmitted from the hub to the weight
through the spacer and spring leaves.
Fig. 3. Removing Balance Weight Assemblies
Fig. 1. Typical Front Balance Weight Mounting
10-2-101
