Bearings are not round.. they have a parting line where the halves meet.. this is the widest part of the Bearing ID.. The point 90Deg to that is the Narrowest part of the bearing..
Lets call the Parting line of the bearing half, 9 - 3 O'clock.. the top and bottom of the bearing will be 6 -12 O'clock.. The bearing surface going from 6 toward about 8 O'clock ( and 6 to 4 O'clock) will be circular. So the hole is 'Round' from about 4 to 8 O'clock.. then will dive out ( get Larger) from 8 to 9 ( 4 to 3 ) to make it's widest point.. Ditto on the Top Half.. You only use ONE strip of Plastigauge per bearing set.. if the Plastigauge is placed at the Six O'clock Position, it will shove the bearing Journal UP into the pocket created by the upper Circular Bearing Half.. your measurement will be proper.. IF you place the Plastigauge at the 7/7:30 Position, it will shove the Crank Journal up and toward the 1/1:30 Position and will SLIGHTLY shove into the shoulder of the bearing step at the 2 to 3 Position, and your measurement will be a little bit Large.. Use the plastigauge at the 6 or 12 position.. on a girdle engine do all bearings at once in the Girdle .. on a Capped Motor, do the caps, and you can do them one at a time. Lay plastigauge all the way across the bearing surface, this will indicate a tapered Journal, or a bearing half that might be cocked in the hole.. As I assemble an engine.. I start putting all the bearings in and check the feel of the rotating crank ( torqued! ) .. then I hang the pistons/rods one at a time but NO rings.. start hanging pistons in in the engine one at a time, and check rotation 'Feel'.. as you start adding pistons/rods, the breakaway torque will increase, but the 'Feel' of the rotating mass should not have any 'Hard Spots'..
As you add pieces, if a hard spot develops, take that piece back out,, check all bearings/ Piston pin motions.. Don't live with a new engine that has a 'Hard Spot'.. it will work it's way out, but what ever was hard is now 'scored' and not smooth.. ONLY after you are very comfortable with the rotating mass smoothness can you finish the assembly.. now remove things and add the rings.. then shit will start getting tight.. Good luck on your build Cj
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