Chapter  4—REDUCTION  GEARS  AND  RELATED  EQUIPMENT prescribed maximum and the bull gear runs in the oil,  the  oil  foams  and  heats  as  a  result  of  the “churning” action. If the oil level is below the prescribed minimum, it may lead to a low lube oil casualty such as a damaged bearing or gears. In  gear  installations  where  the  sump  tank extends’up  around  the  bull  gear,  and  the  normal oil level is above the bottom of the gear, an oil- excluding pan (sheet metal shield) is fitted under the lower part of the gear to prevent its running in the sump oil. Under normal conditions, the bull gear comes in contact with only a small quantity of oil. The oil which tends to fill the pan is swept out by the gear and is drained back to the sump. and  under  close  observation  by  experienced  per- sonnel.  A  more  thorough  investigation  should  be made, as soon as practicable, to determine the cause of the unusual noise. Upon discovery of the trouble,  appropriate  action  should  be  taken  to remedy the condition. Vibration When there is too much oil in the sump, the engines  must  be  slowed  or  stopped  until  the excess oil can be removed and normal conditions restored. Routine checks should be made to see that  the  lubricating  oil  is  maintained  at  the proper  level.  Any  sudden  loss  or  gain  in  the amount of oil should immediately be investigated. If the main reduction gear begins to vibrate, a   complete   investigation   should   be   made, preferably by a naval shipyard. Vibrations may be caused by bent shafts, damaged propellers, misalignment between prime mover and gear, a worn out bearing, or coupling, or an improper balance in the gear train. When these units are built, the gear wheels are carefully balanced (both statically  and  dynamically).  Later  any  unbalance in the gears is manifested either by unusual vibra- tion and noise, or by unusual wear of the bearings. Unusual Noises A properly operating gear has a definite sound which the experienced engine operator can easily recognize. The operator should be familiar with the sounds of the gears aboard the ship during normal  operation  and  at  different  speeds  and under various operating conditions. When a ship has been damaged, vibration of the main reduction gear may result from misalign- ment of the engine and the main shafting as well as from misalignment of the engine and the main gear  foundation. Often the readings of lube oil pressures and temperatures   may   help   in   determining   the reason(s)  for  abnormal  sounds.  A  burned-out pinion bearing or main thrust bearing may be in- dicated by a rapid rise in oil temperature for the individual bearing. A noise may indicate misalign- ment, improper meshing of the gear teeth, or gear tooth damage. When the vibration occurs within the main reduction gear, trouble or damage to the propeller should be one of the first things to consider. The vulnerable  position  of  propellers  makes  them more liable to damage than any other part of the main plant. Bent or broken propeller blading and propellers fouled with line and steel cable may transmit vibration to the main reduction gear. MAINTENANCE OF REDUCTION GEARS When there is either a burned-out bearing or trouble with the gear teeth, the main propeller shaft should immediately be stopped, locked, and inspected to determine the cause of the abnormal sound or noise. The trouble should be remedied before  the  reduction  gear  is  placed  back  in operation. In some cases, conditions of a minor nature may  cause  unusual  noises  in  a  reduction  gear which is otherwise operating satisfactorily. When an investigation reveals the cause of the noise to be minor, the gear should be operated cautiously Under  normal  conditions,  all  repairs  and major  maintenance  on  main  reduction  gears should  be  accomplished  by  a  naval  shipyard. However, when the services of a shipyard are not available,  emergency  repairs  should  be  ac- complished (where possible) either by a repair ship or at an advanced base. Minor inspections, tests, and repairs should be accomplished by the ship’s force. It is of utmost importance that the ship retain a complete record of the reduction gears from the time  of  commissioning.  Complete  installation 4-3