Figure 3-28.—Checking the alignment of a connecting rod.REPAIRING CRANKSHAFTS ANDJOURNAL BEARINGSThe repair of crankshafts and bearings variesdepending on the extent of damage. There is no doubtabout the necessity for replacing such items as brokenor bent crankshafts. Out-of-round journals may bereground and undersize bearing shells may be installed,but this requires personnel skilled in the use of precisiontools. If a new shaft is available, it should be installedand the damaged shaft should be sent to a salvagereclamation center. Under certain conditions, scoredcrankshaft journals or damaged journal bearings may bekept in service if proper repair is performed.Repair of SCORED JOURNALS depends on theextent of scoring. If a crankshaft has been overheated,the effect of the original heat treatment will have beendestroyed. In this case, the crankshaft should bereplaced.If journal scoring is only slight, you can use anoilstone for dressing purposes if you take precautionarymeasures with respect to abrasives during the procedure.During the dressing operation, plug all oil passageswithin the journal and those connecting the mainbearingjournal and the adjacent connecting rod journal.In the dressing procedure, use a fine oilstone,followed with crocus cloth, to polish the surface. Afterdressing journals, always wash them with diesel oil.This procedure must include washing the internal oilpassages as well as the outside journal surfaces. Somepassages are large enough to accommodate a cleaningbrush; smaller passages can be cleaned by blowing themout with compressed air. Always dry the passages byblowing compressed air through them.NEVER STOW A CRANKSHAFT OR BEARINGPART ON ANY METAL SURFACE.When you removea shaft from an engine, place it on a wooden plank withFigure 3-29.—Using a strain or deflection gauge between crankwebs.all journal surfaces protected. If the shaft is to beexposed for some time, protect each journal surface witha coating of heavy grease. Always place bearings onwooden boards or clean cloths.CRANKSHAFT overhaul consists of an inspection,servicing for scoring and wear, and a determination ofeach crank web deflection. Take crank web deflectionreadings according to the Planned Maintenance System(PMS).A strain gauge, often called a crank web deflectionindicator, is used to take deflection readings. The gaugeis merely a dial-reading inside micrometer used tomeasure the variation in the distance between adjacentcrank webs as the engine shaft is barred over. Figure3-29 shows a strain gauge between crank webs.When you install the gauge, or indicator, betweenthe webs of a crank throw, be sure to place the gauge asfar as possible from the axis of the connecting rodjournal. Rest the ends of the indicator in prick-punchmarks in the crank webs. If these marks are not present,make them so that the indicator can be placed in itscorrect position. Consult the manufacturer’s technicalmanual for the proper location of new marks.Readings are generally taken at the four crankpositions: top dead center, inboard, near or at bottomdead center, and outboard. In some engines, it is possibleto take readings at bottom dead center. In others, theconnecting rod may interfere, making it necessary totake the reading as near as possible to bottom deadcenter without having the gauge come in contact withthe connecting rod. When the gauge is in its lowest3-19
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