I have capital "D"'s stamped on the oil pan rail on my 340, what do they mean?

I was told those stampings represent the bearing clearances, A is tighter than B is tighter than C is tighter than D. On my 87 318 I have some stamped AA the rest are A.

Steve

The letters stamped on the pan rail are the measured bore size so the assembler would install the correct size piston.

Due to the tight fit of factory pistons and production tolerances, each finished bore was measured and given a letter disignation of its size; the pistons were also sized accordingly.

For example, an "A" or "B" bore would be slightly under spec, a "D" or "E" bore would be slightly over spec and a "C" would be right on .

This is a cool bit of trivia! I saw those on my 340, and wondered what the heck the source was. It had been gone through once before, and couldn't swear how they got there. That's neat. This thread ought to be part of the resto/engine tech archives!

Clair