Quantcast FIGURE 3-119.  Critical Areas of Crankshaft Load Stress

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ARMY TM 9-2815-255-24 AIR FORCE TO 38G1-95-2 MARINE CORPS TM 2815-24/4 (2) Inspect oil passages to make sure they are open.  Use compressed air and a small piece of wire. (3) Inspect crankshaft for any signs of load stress, cracks, scoring, or scratches on journals.  (An inspection must  be  made  if  the  crankshaft  damper  was  found  to  be  damaged  or  defective.)  FIGURE  3-119  shows critical areas of load stress in a crankshaft. 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 3-119.  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 3-44.3.  Proper undersize bearings should be installed after grinding. 3-177


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