instructions. Afterwards, the bearing cap can be
lowered into position and securely bolted down.
It is possible that the forward bearing for the
inboard pinion is also damaged as a result of
excessive wear. When one pinion bearing fails,
that end of the shaft will tend to move away from
the bull gear; consequently, an abnormal load will
be placed on the other pinion bearing. For this
reason, the other pinion bearing should also be
opened and inspected, and checked with a
micrometer, using the crown thickness method.
All readings should compare with the readings
listed in the manufacturers instructions. If ex-
cessive wear is indicated, the bearing should be
replaced with a new one. If no wear of the
opposite pinion bearing is indicated, then the for-
ward bearing can be reassembled.
The condition of the bearings depends a great
deal upon the type of casualty that has occurred.
When the casualty is due to a loss of lubricating
oil, the pinion bearings must be checked first. If
these bearings are in good condition, it may be
assumed that the bull gear shaft bearings are also
in satisfactory condition. However, after a bear-
ing casualty has been corrected, a close watch
should be maintained on all bearings.
Remember that when the reduction gear is
opened, every precaution should be taken to keep
out dirt and foreign matter and that the repair
personnel should remove all loose articles from
their clothing. Again, before closing the reduc-
tion gear, a careful inspection should be made to
see that the inside of the gear is free of all dirt,
foreign matter, and misplaced tools.
New gears or gears which have been realigned
should be given a wearing-in run at low power
before being subjected to the maximum tooth
pressure of full power.
For the proper operation of the gears, it is
essential that the tooth contact (or total tooth
pressure) be uniformly distributed over the total
area of the tooth faces. This is accomplished by
accurate alignment and adherence to designed
clearances. Gear tooth contact is verified by the
application of Dkem to the gear teeth and by jack-
ing the gears. Then the gears are inspected to
check for the Dkem impressions.
The designed center-to-center distance of the
axes of the rotating elements should be maintained
as accurate as practicable. In all cases the axes
of pinions and gear shafts must be parallel. Non-
parallel shafts concentrate the load in one end of
a helix. This situation may cause flaking, galling,
pitting, featheredge on teeth, deformation of
tooth contour, or breakage of tooth ends.
The designed TOOTH CONTOUR must also
be maintained. If the contour is destroyed, a rub-
bing contact will occur with consequent danger
If proper tooth contact is obtained when the
gears are installed, there will not be much trou-
ble as far as the WEAR OF TEETH is concerned.
Excessive wear cannot take place unless there is
metallic contact, and metallic contact will not
occur if adequate lubrication is provided. An ade-
quate supply of lubricating oil at all times,
proper cleanliness, and inspection for scores will
prevent the wearing of teeth.
If, after all precautions have been taken, the
lubricating oil supply should fail and the TEETH
DO BECOME SCORED, the gears must be
thoroughly overhauled by a naval shipyard, as
soon as possible.
During the first few months that reduction
gears are in service, PITTING may occur, par-
ticularly along the pitch line. Although slight pit-
ting does not affect the operation of the gears,
care must be taken to see that no flakes of metal
are allowed to remain in the oiling system.
Play between the surfaces of the teeth in mesh
on the pitch circle is known as BACKLASH. It
increases as the teeth wear out. However, backlash
can increase considerably without causing any
ROOT CLEARANCE.The designed root
clearance with gear and pinion operating on their
designed centers can be obtained from the
manufacturers drawing or blueprint. The actual
clearance can be found by taking leads or by
inserting a long feeler gage or a wedge gage. This
clearance should check with the designed
clearances. When the root clearance is con-
siderably different at the two ends, the pinion and
gear shaft are not parallel. Some tolerance is per-
mitted, provided that there is still sufficient
backlash and that the teeth are not meshed so
closely that lubrication is adversely affected.
ENGINEMAN 1 & C