Asked in Chevy Caprice Classic
What is the metrology meaning of undersize 20 of a shaft in the US car industry?
I'm going to assume you are talking about a crankshaft. When crank journals get worn or scuffed from wear or dirt in the oiling system or a spun bearing a machine shop can regrind the crankshaft to an under size. For instance lets assume a crankshaft rod journal is 2 inches (2.000) and has some wear, so a machine shop regrinds it to .010 under size and now it measures 1.990 inches, so now you'd need a set of rod bearings to fit a crankshaft that has been reground .010 (ten thousandths of an inch) under size, or twenty thousandths, or whatever the case may be. You would measure the crankshaft main and rod journals with a micrometer to determine if they are standard or have been reground and if it was reground to what size.