instructions. Afterwards, the bearing cap can belowered into position and securely bolted down.It is possible that the forward bearing for theinboard pinion is also damaged as a result ofexcessive wear. When one pinion bearing fails,that end of the shaft will tend to move away fromthe bull gear; consequently, an abnormal load willbe placed on the other pinion bearing. For thisreason, the other pinion bearing should also beopened and inspected, and checked with amicrometer, using the crown thickness method.All readings should compare with the readingslisted in the manufacturer’s instructions. If ex-cessive wear is indicated, the bearing should bereplaced with a new one. If no wear of theopposite pinion bearing is indicated, then the for-ward bearing can be reassembled.The condition of the bearings depends a greatdeal upon the type of casualty that has occurred.When the casualty is due to a loss of lubricatingoil, the pinion bearings must be checked first. Ifthese bearings are in good condition, it may beassumed that the bull gear shaft bearings are alsoin satisfactory condition. However, after a bear-ing casualty has been corrected, a close watchshould be maintained on all bearings.Remember that when the reduction gear isopened, every precaution should be taken to keepout dirt and foreign matter and that the repairpersonnel should remove all loose articles fromtheir clothing. Again, before closing the reduc-tion gear, a careful inspection should be made tosee that the inside of the gear is free of all dirt,foreign matter, and misplaced tools.Gear TeethNew gears or gears which have been realignedshould be given a wearing-in run at low powerbefore being subjected to the maximum toothpressure of full power.For the proper operation of the gears, it isessential that the tooth contact (or total toothpressure) be uniformly distributed over the totalarea of the tooth faces. This is accomplished byaccurate alignment and adherence to designedclearances. Gear tooth contact is verified by theapplication of Dkem to the gear teeth and by jack-ing the gears. Then the gears are inspected tocheck for the Dkem impressions.The designed center-to-center distance of theaxes of the rotating elements should be maintainedas accurate as practicable. In all cases the axesof pinions and gear shafts must be parallel. Non-parallel shafts concentrate the load in one end ofa helix. This situation may cause flaking, galling,pitting, featheredge on teeth, deformation oftooth contour, or breakage of tooth ends.The designed TOOTH CONTOUR must alsobe maintained. If the contour is destroyed, a rub-bing contact will occur with consequent dangerof abrasion.If proper tooth contact is obtained when thegears 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 ismetallic contact, and metallic contact will notoccur if adequate lubrication is provided. An ade-quate supply of lubricating oil at all times,proper cleanliness, and inspection for scores willprevent the wearing of teeth.If, after all precautions have been taken, thelubricating oil supply should fail and the TEETHDO BECOME SCORED, the gears must bethoroughly overhauled by a naval shipyard, assoon as possible.During the first few months that reductiongears 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 metalare allowed to remain in the oiling system.Play between the surfaces of the teeth in meshon the pitch circle is known as BACKLASH. Itincreases as the teeth wear out. However, backlashcan increase considerably without causing anytrouble.ROOT CLEARANCE.—The designed rootclearance with gear and pinion operating on theirdesigned centers can be obtained from themanufacturer’s drawing or blueprint. The actualclearance can be found by taking leads or byinserting a long feeler gage or a wedge gage. Thisclearance should check with the designedclearances. When the root clearance is con-siderably different at the two ends, the pinion andgear shaft are not parallel. Some tolerance is per-mitted, provided that there is still sufficientbacklash and that the teeth are not meshed soclosely that lubrication is adversely affected.ENGINEMAN 1 & C4-6
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