TM 9-6115-604-34NAVFAC P-8-633-34(18)Back the wheel out and traverse over to the other side of the journal. Feed the wheel in until it just touchesthe journal, and then traverse over until it just starts to grind the fillet area, and just touches the journal sidewall.(19)Feed the wheel in slowly until the feed indicator reaches 0, and spark-out has occurred. Back the wheel out,and check the journal. When checked with an outside micrometer, the journal shall be the correct undersize,and have no detectable step at the point of wheel overlap.CAUTIONExcessive grinding of either bossing wall will allow the connecting rod to boss on the pistonrather than on the crankshaft as It should. Such a condition may cause excessive oilconsumption, uneven wear, or failure of the connecting rod bearings and possible seizure of theengine. Grinding of the journal bossing surfaces Is permissible as long as the dimensionaltolerances (Figure 9-51) are not exceeded.(20)If the connecting rod bossing surfaces need further grinding, traverse the grinding wheel to remove thedefects. When grinding the bossing surfaces, do not exceed the dimensions given in Figure 9-51.(21)Check the fillet radii using fillet ball gages 3375241 and 3375242 as follows (see Figure 9-52):(a)Place the 0.230 inch (5.84 mm) ball on the journal close to the fillet, and place a light behind the ball.One dark spot will be noted at the point of contact between the ball and the journal surface.(b)Move the ball gage toward the fillet. If the fillet is properly blended, and at or above the minimumradius, only one point of contact should show as the ball contacts the fillet area and moves up to thebossing wall (A, Figure 9-52). If two points of contact show at any part of the radius, the radius isundersize.(c)Check the fillet with the 0.270 inch (6.86 mm) ball gage to ensure that it is not oversize. On this checktwo points of contact should show: one at the bottom and the other up on the side (B, Figure 9-52). Ifonly one point of contact shows at any part of the radius, the radius is oversize.(d)If fillet radius is incorrect, the grinding wheel was improperly dressed. Refer to step (2), above, forproper grinding wheel dressing.NOTEAlternate each rod bearing journal as to which cut is made first. If, on the first bearing journal,the right side was full width cut, then, on the next rod journal make the full width cut on the leftside. This results in a more even breakdown of the grinding wheel and aids in producing a goodsurface finish on the reground journals.(22)Grind all other connecting rod journals in accordance with steps (9) through , above.(23)Crankshaft throw index is the relation of the crankshaft throws to each other and the front crankshaft keyway,and should be 119 degrees 49 minutes to 120 degrees 11 minutes. Any incorrect crankshaft throw index isan indication of twist that may have occurred during machining operations. For inspection purposes, checkfor crankshaft twist by measuring the difference between the front and rear throws as follows:(a)Turn the crankshaft in the grinding machine so that the front throw is at top center as measured with ahorizontal vee gage. Lock the crankshaft in this position and note the indicator reading.(b)Move the horizontal vee gage to the rear throw and note the indicator reading. If the deviation fromfront to rear throw is over 0.033 inch (0.84 mm), the crankshaft has excessive twist and must bereplaced.NOTEAll main bearing journals on the crankshaft shall be ground to the same undersize.(24)Move the head stock and tail stock alternately and evenly, and relocate the main bearing centerline of thecrankshaft to the centerline of the crankshaft grinding machine (A, Figure 9-50).9-89
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