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TM 55-1905-221-14-3
a. Balance Weight Cover.
The front balance weight cover encloses the front engine balance weights and also serves as a support for the heat
exchanger and engine brace.
The balance weight cover requires no servicing. However, when an engine is being completely reconditioned, or the
camshaft, balancer shaft, or front balance weights need replacing, the balance weight cover must be removed.
b. 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 part 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 its entire speed range.
Each set of weights (weights on one shaft comprise a set) rotates in an opposite direction with respect to the other.
When the two weights at either end of the engine are in a vertical plane, their centrifugal forces are in the same direction
and oppose the unbalanced couple; when they are in a horizontal plane, the centrifugal forces of these balance weights
are opposite and are therefore cancelled. The front balance weights are eccentric in a direction opposite to the rear
balance weights; therefore, rotation will result in the desired couple, effective only in a vertical plane.
The balance weights consist of two eccentric weights at each end of the engine. On six cylinder engines, additional
weights are attached to the gears. The front balance weights are keyed to the front end of the camshaft and balance
shaft. The front balance weights must be removed whenever the camshaft or balance shaft is removed.


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