Chapter 4—REDUCTION GEARS AND RELATED EQUIPMENTprescribed maximum and the bull gear runs in theoil, the oil foams and heats as a result of the“churning” action. If the oil level is below theprescribed minimum, it may lead to a low lubeoil casualty such as a damaged bearing or gears.In gear installations where the sump tankextends’up around the bull gear, and the normaloil level is above the bottom of the gear, an oil-excluding pan (sheet metal shield) is fitted underthe lower part of the gear to prevent its runningin the sump oil. Under normal conditions, the bullgear comes in contact with only a small quantityof oil. The oil which tends to fill the pan is sweptout by the gear and is drained back to the sump.and under close observation by experienced per-sonnel. A more thorough investigation should bemade, as soon as practicable, to determine thecause of the unusual noise. Upon discovery of thetrouble, appropriate action should be taken toremedy the condition.VibrationWhen there is too much oil in the sump, theengines must be slowed or stopped until theexcess oil can be removed and normal conditionsrestored. Routine checks should be made to seethat the lubricating oil is maintained at theproper level. Any sudden loss or gain in theamount 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 maybe caused by bent shafts, damaged propellers,misalignment between prime mover and gear, aworn out bearing, or coupling, or an improperbalance in the gear train. When these units arebuilt, the gear wheels are carefully balanced (bothstatically and dynamically). Later any unbalancein the gears is manifested either by unusual vibra-tion and noise, or by unusual wear of the bearings.Unusual NoisesA properly operating gear has a definite soundwhich the experienced engine operator can easilyrecognize. The operator should be familiar withthe sounds of the gears aboard the ship duringnormal operation and at different speeds andunder various operating conditions.When a ship has been damaged, vibration ofthe main reduction gear may result from misalign-ment of the engine and the main shafting as wellas from misalignment of the engine and the maingear foundation.Often the readings of lube oil pressures andtemperatures may help in determining thereason(s) for abnormal sounds. A burned-outpinion bearing or main thrust bearing may be in-dicated by a rapid rise in oil temperature for theindividual bearing. A noise may indicate misalign-ment, improper meshing of the gear teeth, or geartooth damage.When the vibration occurs within the mainreduction gear, trouble or damage to the propellershould be one of the first things to consider. Thevulnerable position of propellers makes themmore liable to damage than any other part of themain plant. Bent or broken propeller blading andpropellers fouled with line and steel cable maytransmit vibration to the main reduction gear.MAINTENANCE OFREDUCTION GEARSWhen there is either a burned-out bearing ortrouble with the gear teeth, the main propellershaft should immediately be stopped, locked, andinspected to determine the cause of the abnormalsound or noise. The trouble should be remediedbefore the reduction gear is placed back inoperation.In some cases, conditions of a minor naturemay cause unusual noises in a reduction gearwhich is otherwise operating satisfactorily. Whenan investigation reveals the cause of the noise tobe minor, the gear should be operated cautiouslyUnder normal conditions, all repairs andmajor maintenance on main reduction gearsshould be accomplished by a naval shipyard.However, when the services of a shipyard are notavailable, emergency repairs should be ac-complished (where possible) either by a repair shipor at an advanced base. Minor inspections, tests,and repairs should be accomplished by the ship’sforce.It is of utmost importance that the ship retaina complete record of the reduction gears from thetime of commissioning. Complete installation4-3
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