[rotorwrench]

The rods & caps are tinned prior to pouring babbitt. Sometimes they don't get a good tin job and the babbitt doesn't stick as well as it should. Even with everything well coated a bearing can experience cracking & chipping of the babbitt if the bearings are well worn or the babbitt is thin.

Shimming is done for several reasons. The most common reason is to be able to tighten a worn bearing set by removing a shim or shims. The other reason is that folks had a tendency to sand the parting surface the cap on a flat piece of glass if the shims were all gone instead of exchanging them for a rebuilt set. This makes the next babbitt job too thin so more shims have to be used to keep from hitting steel while cutting the bores to size.