Why are there holes in my engine?
Can you tell me what these two holes are for? They are about a quarter of an inch deep and are unthreaded. One is on the oil pan flange and the other one is in the side of the block. Most six-cylinder Chevy engines have them.
Sometimes the machined holes were for accessories that your vehicle didn’t have or for applications other than yours. It was sometimes more efficient to drill all blocks the same regardless of which vehicle it was destined for or which transmission it would be coupled to or which side the generator bracket would be bolted to.
Most often, however, the drilled but untapped holes were used during the manufacturing process, to precisely locate the block while it was being machined.