1.7
DETROIT DIESEL 53
ENGINE BALANCE AND BALANCE WEIGHTS
In the balance of two-cycle engines, it is important to
Remove Front Balance Weights
consider disturbances due to the reciprocating action
1. Remove the nut at each end of both shafts as
of the piston masses. These disturbances are of two
outlined in Section 1.7.2.
kinds: unbalanced forces and unbalanced couples.
These forces and couples are considered as primary or
2. Force the balance weight off the end of each shaft,
secondary according to whether their frequency is
using two screw drivers or pry bars between the
equal to engine speed or twice engine speed. Although
balance weight and the upper front cover as shown in
it is possible to have unbalanced forces or couples at
Fig. 1.
frequencies higher than the second order, they are of
small consequence in comparison to the primary forces
and couples. Even the secondary forces and couples
Install Front Balance Weights
are usually of little practical significance.
1. Reinstall the Woodruff keys in the shafts, if they
The reciprocating masses (the piston and upper end of
were removed.
the rod) produce an unbalanced couple due to their
arrangement on the crankshaft.
2. Align the keyway in the balance weight with the key
in the shaft, then slide the weight on the shaft. If the
On an In-line engine, it
weight does not slide easily onto the shaft, loosen the
tends to rock the engine from end to end in a vertical
thrust washer retaining bolts at the opposite end of the
plane. This couple is cancelled by incorporating an
shaft. Then, to prevent possible damage to the thrust
integral crankshaft balance component and by placing
washer, support the rear end of the shaft while
balance weights
tapping the weight into place with a hammer and a
at the outer ends of the balance shaft
and camshaft (In-line engine). This balance arrange-
ment produces a couple that is equal and opposite in
magnitude and direction to the primary couple.
balance shaft and
On the
camshaft (In-line engine), each set of weights (weights
on the outer ends of each shaft comprise a set) rotates
in an opposite direction with respect to the other.
When the weights on either end of the engine are in a
vertical plane, their centrifugal forces are in the same
direction and oppose the primary couple. When they
are in a horizontal plane, the centrifugal forces of
these balance weights oppose each other and are,
therefore, cancelled. The front balance weights act in a
direction opposite to the rear balance weights;
therefore, rotation will result in a couple effective only
in a vertical plane. This couple; along with that built
into the crankshaft, forms an elliptical couple which
completely balances the primary couple.
The balance weights are integral with the gears and
the circular balance weights (pulleys) on the shafts.
Additional weights are attached to the camshaft and
balance shaft gears on
three
cylinder
engines.
Both the rotating and primary reciprocating forces
and couples are completely balanced in the engines.
Fig. 1 - Removing Front Balance Weight (Pulley
Consequently, the engines will operate smoothly and
Type)
in balance throughout their entire speed range.
SEC. 1.7 Page 1
November, 1973
