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 manufacturer’s 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. Gear  Teeth 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 of  abrasion. 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 trouble. ROOT CLEARANCE.—The designed root clearance with gear and pinion operating on their designed   centers   can   be   obtained   from   the manufacturer’s  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 4-6