ALIGNMENT OF GEAR TEETH.When
the gear and the pinion are parallel (axes of the
two shafts are in the same plane and equally dis-
tant from each other), the gear train is aligned.
In service the best indication of proper alignment
is good tooth contact and quiet operation.
The length of tooth contact across the face of
the pinions and gears is the criterion for satisfac-
tory alignment of reduction gears. To static check
the length of tooth contact, coat about 5 to 10
teeth with either Prussian blue or red lead, then
roll the gears together with sufficient torque to
cause contact between the meshing teeth and force
the journals into the ahead reaction position in
their bearings. After you determine the tooth con-
tact, remove all the coating to prevent possible
contamination of the lubricating oil. If tooth con-
tact is to be checked under operating conditions,
coat the teeth with red or blue Dyken or with cop-
SPOTTING GEAR TEETH.All abnormal
conditions which may be revealed by operational
sounds or by inspections should be corrected as
soon as possible. Rough gear teeth surfaces,
resulting from the passage of foreign objects
through the teeth, should be stoned smooth. If
the deterioration of a tooth surface cannot be
traced directly to a foreign object, give special at-
tention to lubrication and to the condition of the
bearings. Also consider the possibility that a
change in the supporting structure may have
disturbed the parallelism of the rotors.
Spotting reduction gear teeth is done first by
coating the teeth with Prussian blue and then by
jacking the gear in its ahead direction of rotation.
As the gear teeth come in contact with the
marked pinion teeth, an impression is left on the
high part of each gear tooth. Rotate the gear
about 1/4 of a turn to a convenient position for
stoning. Then remove all the high spots indicated
by the marking with a small handstone. Normally,
it will be necessary to replace the bluing on the
pinion teeth repeatedly, since if the bluing is
applied too heavily you may obtain false impres-
sions on the gear teeth.
A satisfactory tooth contact is obtained when
at least 80% of the axial length of the working
face of each tooth is in contact and distributed
over approximately 100% of the face width.
Remember that the stoning of gears is useful
only to remove a local hump or deformation, not
to remove deep pitting or galling.
Main Thrust Bearings
A ship is moved through the water by an ax-
ial thrust that is developed by the propeller and
transmitted to the ships structure. This axial
thrust is transmitted by the shaft through a thrust
bearing which is located either at the forward end
or at the after end of the main reduction bull gear
or in the propeller line shafting aft of the gear.
Pivoted-segmental shoe bearings (Kingsbury type)
utilize a wedge-shaped film of oil in their opera-
tion. The source of lubricating oil for thrust bear-
ings depends on the location of the bearings. In
some installations oil is provided by the same
system which furnishes oil to the reduction gears.
In other installations, a separate lubricating
system is provided.
Kingsbury-type thrust bearings consist of a
collar mounted on the shaft and revolving between
one or more sets of babbitt-faced segmental shoes.
The backs of these shoes rest against round
hardened steel pivots which permit the shoes to
assume a tilt and change their angle with respect
to the shaft collar. Bearings in which the thrust
is always exerted in the same direction are
equipped with shoes on one side only, but since
provision must be made in most marine applica-
tions for thrust in two directions, it is more com-
mon to find shoes on each side of the collar. The
shoes are free to adjust themselves at an angle to
the collar. Rotation of the shaft collar drags a film
of oil into the space between the shoes and the
collar, and as the oil film forms, the shoes adjust
themselves to the angle most efficient for the load
conditions and the oil viscosity.
Additional information on Kingsbury-type
thrust bearings and other types of bearings is pro-
vided in the NAVSHIPS Technical Manual,
chapter 243. Detailed information on allowable
tolerances and procedures for taking thrust bear-
ing readings can be obtained from the manufac-
turers technical manual.
End play checking of a Kingsbury thrust bear-
ing must always be done with the upper half of
the housing solidly bolted down, otherwise the
base rings may tilt and provide a false reading.
Chapter 4REDUCTION GEARS AND RELATED EQUIPMENT