TM 5-3805-260-24CHECKING ROTOR TIP CLEARANCECRANKSHAFTReconditioning of the crankshaft can be done bygrinding the "journals" (bearing surface on the crankshaftfor the connecting rod bearings and main bearings) .010in. (0.25 mm), .020 in. (0.51 mm) or .050 in. (1.27 mm)’undersize" (smaller than the original size).The diameter of the "journals’ for the connecting rodbearings is 2.7496 .0006 in. (69.840 0.015 mm). Thediameter of the "journals" for the main bearings is 3.4995.0006 in. (88.887 0.015 mm). The minimumpermissible diameter of the "journals" for the connectingrod is 2.7486 in. (69.814 mm). The minimum permissiblediameter of the "journals" for the main bearings is 3.4985in. (88.862 mm). Measure each "journal" in severalplaces around the diameter to find the maximum wearpoint. If the diameter of any "journal" is smaller than theminimum permissible diameter, grind all of the "journals."Before grinding a crankshaft, check the crankshaft forbeing straight. To check a crankshaft for being straight,support each end main bearing "journal" in V-blocks.Using a dial indicator, position the indicator at the zeroreading then measure the total indicator reading at theother three main bearing "journals." The maximum totalindicator reading is .008 in. (0.20 mm) at the center mainbearing "journal" and .004 in. (0.10 mm) at the other twomain bearing "journals." If total indicator reading is morethan that given but less than .030 in. (0.76 mm) thecrankshaft can be "straightened" (made straight). Before"straightening" (making straight) a crankshaft gettemperature of the crankshaft to 400°F (204°C). For thespecifications for grinding a crankshaft, see the topicCRANKSHAFT GRINDING SPECIFICATIONS.With the crankshaft installed in the cylinder block,check the end play for the crankshaft. End play for thecrankshaft is .003 to .010 in. (0.08 to 0.25 mm).Maximum permissible end play for the crankshaft is .014in. (0.36 mm).NOTE: If end play for the crankshaft is more than themaximum permissible end play, check the crankshaftthrust bearing.CRANKSHAFT GRINDING SPECIFICATIONSThe dimensions and finish for grinding crankshaftsare as follows:Diameter (A) for connecting rod bearing journals is;.010 in. (0.25 mm)Undersize ................................2.7396 + .0006 in.(69.586 + 0.015 mm).020 in. (0.51 mm)Undersize ................................ 2.7296 .0006 in.(69.332 0.015 mm).050 in. (1.27 mm)Undersize ................................ 2.6996 .0006 in.(68.570 + 0.015 mm)Surface finish must be 10 micro inches (0.25micrometers) or less.Radius (B) must be . 100 .010 in. (2.54 0.25 mm).Surface finish must be 63 micro inches (1.6micrometers) or less.The radius must blend smoothly with the newly machinedjournals.DIMENSIONS FOR GRINDINGA. Diameter of connecting rod bearing journals. B.Radius on connecting rod bearing journals. C. Widthto grind journals for the connecting rods. D.Diameter of main bearing journals. E. Radius onmain bearing journals. F. Width to grind journals forthe main bearings.Width (C) is 2.314 .003 in. (58.77 0.08 mm)Diameter (D) for main bearing journals is:.010 in. (0.25 mm)Undersize ................................ 3.4895 .0006 in.(88.633 0.015 mm).020 in. (0.51 mm)Undersize ................................ 3.4795 .0006 in.(88.379 0.015 mm).050 in. (1.27 mm)Undersize ................................ 3.4495 .0006 in.(87.617 0.015 mm)3-386
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