Placing very carefully shepherded shims into place prior to installing the crossbox cap. The crossbox sleeves were bored with the shim packs in place, with the bolts torqued tight. When setting up for boring, the shims were chosen to be under pressure only after the unbored sleeves were already compressed into the crossboxes. The reasoning for this was to force the sleeves, turned a few thousandths larger than the theoretical crossbox hole size, and force them to conform to crossbox bores that are somewhat less than pristine (worn), to securely immobilize the sleeves so they will not continually be "working" in their housings as the locomotive is under way. Essentially, the sleeves were bored (round) while they were squeezed out of shape, and in order for them to become round again at assembly, great care had to be taken to not get the shim packs mixed around.

Photo by Bill Liebman