NOTE Straightening of used rods that are bent beyond 0.004 inch and up to a maximum of 0.030 inch is acceptable. Bridge the rod to be straightened at the pin and crank ends and bend rod in the center of the I-beam section. Do not nick or indent the rod surfaces during this operation. Always bend beyond the straight position and then bend back to the straight position. A hydraulic press or fix- ture can be satisfactorily used for this operation. (6)  The  twist  of  the  connecting  rod  can  be checked with a feeler gauge between the pin mandrel and fixture face. A twist up to 0.010 inch maximum is accept- able. l.  Make  certain  oil  hole  in  connecting  rod  is  clean and free of foreign matter. Blow dry compressed air through  hole. m. Inspect connecting rod bearing shells for scoring, chipping, corrosion, cracking, or signs of overheating; discard bearing shells if any of these conditions are appar- ent. The backs of bearing shells should be inspected for bright spots and discarded if any bright spots are found; this condition indicates that bearing shells have been mov- ing in their supports, a.  Inspect  rod  bearing  shells  for  wear.  The  bore  of bearing shells is 2.7495 to 2.7510 inches installed and with connecting rod bolts tightened to the specified torque of 80 to 85 foot-pounds. This provides a running clear- ance of 0.001 to 0.0035 inch. New bearing shells must be installed when this clearance exceeds 0.008 inch. Q.  Measure  connecting  rod  bearing  shells  for  wear with a micrometer at several places away from the parting line. Bearing shells, when in place, are 0.0004 to 0.001 inch larger in diameter for a distance of 3/8 inch each side of the parting line than they are 90° from the parting line, Connecting rod bearings have a thickness of 0,10975 to 0.11025 inch. Shells measuring less than 0.108 inch should be discarded and new ones installed. In the event that the crankshaft is worn or damaged and must be ground, bearing shells 0.002 inch, 0.010 inch, 0.020 inch and 0.040 inch undersize are available. NOTE Install new bearing shells if the fit is unsatisfac- tory. The crankshaft must turn freely after all the connecting rod socket head cap bolts have been tightened to torque of 80 to 85 foot-pounds or 12 point  cap  screws  torque  to  65-65.5. p.  Replace  rod  bearings  if  they  have  been  removed and have given 2000 hours or more service. Always replace rod bearings when rebuilding engine at depot maintenance level. g. If the connecting rod bushing is worn it must be pressed out and a new bushing pressed into the connecting rod. When new bushing are installed, be sure the bushing oil hole lines up with the ccm.netting rod oil hole. The outer diameter of a new piston pin is 1.5011 to 1.15013 inches and the bore of the bushing is 1.5027 to 1.5032 inches. These dimensions provide a running clearance of 0.0014 to 0.0021 inch between the pin and the bushing. It is necessary to ream the connecting rod bushing to obtain this clearance The bore in the piston for the piston pin is 1.5014 to 1.5016 inches. These dimensions provide a fit of pin in piston at room temperature of 0.001 inch loose to 0.0005 inch loose. 14-83   Piston,   Rod,   and   Rod   Bearing   Reassembly   and Installation. When  installing  rings  on  pistons,  do  not  spread the  rings  more  than  necessary.  Whenever  a connecting  rod  with  the  piston  is  secured  in  a vise,  be  extremely  careful  that  the  bottom  of the  piston  skirt  is  not  nicked.  Use  lead  protec- tive  jaws  to  protect  the  bottom  of  the  skirt from  nicks  and  also  to  prevent  nicks  in  the  rod which  will  lead  to  piston  and/or  connecting  rod failure. a. Install the three piece oil control ring as follows: (1)  Place  stainless  steel  expander  spacer  of three-piece ring in the bottom groove of the piston with the ends butted. (2)  Install  chrome-plated  steel  segment  on  the bottom side of expander spacer, with gap of segment approximately 90° beyond gap of expander spacer, making certain expander spacer is still in a butted position. (3) Install second segment on the top side of expander spacer with segment gap approximately 90° from expander spacer gap in opposite direction from which the bottom segment has been installed. b.  Install  the  three  compression  rings.  The  gap  of all rings must be positioned 180° apart and in line with the piston pin holes. c.  Recheck  the  three-piece  ring  assembly.  Rings should be free to move in the grooves; however, a slight drag will be evident because of the side sealing action of the ring assembly. Be sure the expander spacer remains in butted  position, NOTE Pistons must be fitted to their respective cylinder sleeves before the piston rings are installed to provide a running   clearance   of   not   less   than 0.0025 inch. Insufficieint clearance will result in premature failure of pistons and/or cylinder sleeves. Measurements must be taken at room temperature. 14-90   Change   12