The term "Babbit" applies to several different soft metal alloys of lead, copper, tin and antimony. Depending on the percentage of each metal used it can vary from soft enough to scratch with a fingernail to very hard. The alloy used in Chevy connecting rods is called "high speed Babbit" and it's pretty hard, durable stuff. A layer of the soft metal is bonded to the big end of the connecting rod and the rod cap, then bored to the size of the crankshaft journal. Shims are placed between the rod and the cap to allow for oil clearance so the bearing can be lubricated by a dipper attached to the rod cap. It lubricates the rod by dipping into a trough attached to the oil pan at idle speed, and a stream of oil squirts directly into the dipper at higher speeds. When the Babbit metal wears, shims can be removed to regain the proper clearance.
Later model engines such as the 54-up 235's and newer have the Babbit bonded to a removable steel backing, rather than being bonded directly to the rod. These can be replaced without changing the rods. There is a conversion bearing available for the dipper-equipped engines for removable bearings, but the Babbited rods require some custom machining to use them. Pull a rod cap and see if there's a removable insert. If so, you've got modified rods. If not, reassemble the rod with exactly the same number and placement of shims you found when it was disassembled to maintain the proper oil clearance.
Jerry
