Tightening the journal box pedestal bolts, in order to snug things together for checking the gap between the side frame bars, and the tiebar. The tiebar needs a bit of welding to straighten things up, and to make a nicer, closer fit. The corner bolts could be tightened down, but this would pull the bars of the side frame out of relaxation, and put them in permanent strain, fostering breakage. This corner joint is a dynamic joint, meaning that it constantly moves as the locomotive rolls along the track, and the bolts must not be tightened to the point that the motion between the side frame and the tiebar is eliminated, or something WILL break. As the two opposite side frame assemblies rise and fall with the axles as they adjust themselves to the uneven track, the ends of the side frames retard and advance relative to each other, causing the tiebar to momentarily shift from its theoretical 90 degree angle across the truck. If this small but almost constant motion is restricted or eliminated, something 's gotta give.

Photo by Bill Liebman