Today, I was trying to check if a stock crankshaft that I have in the garage was for a RB or SB. I pulled out my Harbor Freight calipers and measured 2.12" for the rod journals and 2.49" for the main journals. After doing some online research, I determined it was a SB crankshaft.

Looking for some expertise from the Moparts Forum on how to quickly identify a stock RB forged crankshaft from a SB (or B vs. RB)? Are there some unique features between the two crankshafts that I should focus on during review? Definitely would help during a swap meet when I forgot the calipers at home.

Thank you advance for the feedback!

First thing that comes to mind is the balancer bolt. Small block takes a much longer bolt with a long shank. I don't have a big block crank out of an engine right now, but the threads should be much closer to the end of the crank on a big block.

Measure how long that small block crank is. Overall, and the rear flange and main seal areas. Since you have it get to know it well. Look at it, study it, memorize it,

Use your factory service manual for the journal diameters.

There is a quick way to tell the difference, a big block has a 1 1/4" collar in front of the front main bearing journal (pic), small block (2nd pic) doesn't have it.