Quantcast FIGURE 3-138.  Critical Areas of Crankshaft Load Stress

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ARMY TM 9-2815-256-24 AIR FORCE TO 38G1-96-2 MARINE CORPS TM 2815-24/5 NOTE When inspecting crankshaft for cracks, a method (such as the Fluorescent Magnetic Particle Method) must be used that is capable of detecting minute cracks that are not visible to the eye.  This method magnetizes the crank, employing magnetic particles which are fluorescent and glow under black light. Replace crankshaft if cracks are found.  The crankshaft must be demagnetized after the test. (4) Check  each  journal  for  evidence  of  excessive  overheating  or  discoloration.    If  either  condition  exists, replace crankshaft since heat treatment has probably been destroyed. FIGURE 3-138.  Critical Areas of Crankshaft Load Stress d. Measure assembled ID of bearings and OD of crankshaft journals as follows: (1) With  crankshaft  out  of  engine  block,  install  main  bearing  inserts  and  caps  (be  sure  inserts  are  installed correctly). (2) Tighten main bearing capscrews to 85 ft-lbs (115 Nm). (3) Measure ID of all bearings with an inside micrometer.  ID of assembled insert should be 3.125 to 3.127 inches (79.39 to 79.44 mm). (4) Measure OD of all respective crankshaft journals at several points around journal.  OD of main bearing journal should be 3.123 to 3.124 inches (79.34 to 79.36 mm). NOTE If  engine  has  previously  had  a  major  overhaul  and  undersized  bearing  inserts  were  used,  above listed ID and OD dimensions may not be the same as those recorded.  However, oil clearance should be within specifications.  Oil clearance is 0.0012 to 0.004 inch (0.030 to 0.10 mm).  The maximum serviceable clearance is 0.006 inch (0.15 mm). (5) Use crankshaft journal OD measurements to determine if journal is out-of-round or tapered.  Journal out- of-roundness  wear  limit  is  0.003  inch  (0.08  mm).    Journal  taper-per-inch  of  journal  length  wear  limit  is 0.0001 inch (0.025 mm) (6) If   journals   are   tapered,   out-of-round,   scored,   or   damaged,   crankshaft   should   be   ground.      Refer   to paragraph 3-43.3.  Proper undersize bearings should be installed after grinding. e. Measure main thrust journal width and thrust bearing width, refer to FIGURE 3-139, as follows: (1) Measure width of main thrust journal with an inside micrometer. (2) New main thrust journal width is 1.531 to 1.535 inches (38.90 to 39.00 mm). (3) If width is not within specification, recondition crankshaft and install an oversize thrust washer set.  If width is correct, measure main thrust bearing width. 3-184


 


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