Chapter 5-FUNDAMENTALS OF SHIP PROPULSION AND STEERING 



must be checked to determine interchangeability 

 of gear bearings. 



Special tools and equipment needed to lift 

 main reduction gear covers, to handle the quill 

 shaft when removing bearings from it, and to 

 take required readings and measurements, are 

 normally carried aboard. The special tools and 

 equipment should always be aboard in case 

 emergency repairs have to be made by repair 

 ships or bases not required to carry these items. 



The manufacturer's technical manual is the 

 best source of information concerning repairs 

 and maintenance of any specific reduction gear 

 installation. Chapters 9420, 9430, and 9440 of 

 NavShips Technical Manual gives the inspection 

 requirements for reduction gears, shafting, 

 bearings, and propellers. 



The inspections mentioned here are the mini- 

 mum requirements only. Where defects are sus- 

 pected, or operating conditions so indicate, in- 

 spections should be made at more frequent 

 intervals. 



To open any inspection plates or other fit- 

 tings of the main reduction gears, permission 

 should first be obtained from the engineer of- 

 ficer. Before replacing an inspection plate, 

 connection, or cover which permits access to 

 the gear casing, a careful inspection shall be 

 made by an officer of the engineering department 

 to ensure that no foreign matter has entered or 

 remains in the casing or oil lines. If the work is 

 being done by a repair activity, an officer from 

 the repair activity must also inspect the gear 

 casing. An entry of the inspections and the name 

 of the officer or officers must be made in the 

 Engineering Log. The inspections required on 

 the main engine reduction gears are shown on 

 the Maintenance Index Page, figure 5-23. 



The importance of proper gear tooth contact 

 cannot be overemphasized. Any abnormal con- 

 dition which may be revealed by operational 

 sounds or by inspections should be corrected 

 as soon as possible. Any abnormal condition 

 which is not corrected will cause excessive wear 

 which may result in general disintegration of the 

 tooth surfaces. 



If proper tooth contact is obtained when the 

 gears are installed, little wear of teeth will 

 occur. Excessive wear cannot take place without 

 metallic contact. Proper clearances and ade- 

 quate lubrication will prevent most gear tooth 

 trouble. 



If proper contact is obtained when the gears 

 are installed, the initial wearing, which takes 

 place under conditions of normal load and ade- 



quate lubrication, will smooth out rough and 

 uneven places on the gear teeth. This initial 

 wearing-in is referred to as NORMAL WEAR 

 or RUNNING IN. As long as operating condi- 

 tions remain normal, nofurther wear will occur. 



Small shallow pits starting near the pitch 

 line, will frequently form during the initial stage 

 of operation; this process is called INITIAL 

 PITTING. Often the pits (about the size of a 

 pinhead or even smaller) can be seen only under 

 a magnifying glass. These pits are not detri- 

 mental and usually disappear in the course of 

 normal wear. 



Pitting which is progressive and continues 

 at an increasing rate is known as DESTRUCTIVE 

 PITTING. The pits are fairly large and are rel- 

 atively deep. Destructive pitting is not likely to 

 occur under proper operating conditions, but 

 could be caused by excessive loading, too soft 

 material, or improper lubrication. It is usually 

 found that this type of pitting is due to misalign- 

 ment or to improper lubrication. 



The condition in which groups of scratches 

 appear on the teeth (from the bottom to the top 

 of the tooth) is termed abrasion, or scratching. 

 It may be caused by inadequate lubrication, or 

 by the presence of foreign matter in the lubri- 

 cating oil. When abrasion or scratching is noted, 

 the lubricating system and the gear spray fix- 

 tures should immediately be examined. If it is 

 found that dirty oil is responsible, the system 

 must be thoroughly cleaned andthe whole charge 

 of oil centrifuged. 



The term "scoring" denotes a general rough- 

 ening of the whole tooth surface. Scoring marks 

 are deeper and more pronounced than scratching 

 and they cover an area of the tooth, instead of 

 occurring haphazardly, as in scratching or abra- 

 sion. Small areas of scoring may occur in the 

 same position on all teeth. Scoring, with proper 

 alignment and operation, usually results from 

 inadequate lubrication, and is intensified by the 

 use of dirty oil. If these conditions are not cor- 

 rected, continued operation will result in a gen- 

 eral disintegration of the tooth surfaces. 



Under normal conditions all alignment in- 

 spections and checks, plus the necessary re- 

 pairs, are accomplished by naval shipyards. 

 Incorrect alignment will be indicated by ab- 

 normal vibration, unusual noise, and wear of the 

 flexible couplings or main reduction gears. When 

 misalignment is indicated, a detailed inspection 

 should be made by shipyard personnel. 



Two sets of readings are required to get an 

 accurate check of the propulsion shafting. One 



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