How to tell B and RB cranks apart without tools??

Is there an easy method of ID'ing B and RB crankshafts? I can't tell them apart by eye, and don't have the proper measuring tools.

Thanks for any help.

Yes, by the casting numbers.

You don't have a tape measure?

The main bearing journals are smaller on the B cranks. RBs are 2.750, Bs are 2.675? An RB crank will have a circumference of 8.639 inch, or 8 5/8 plus a touch.

^^^ cut a strip of paper & measure the circumference then divide Pi into that for the journal diameters Greg posted.

You don't have to measure anything.

If the rear main bearing journal is almost the same diameter as the rear main seal journal, you have an RB crank.

If the main bearing journal is noticeably smaller, you have a B crank.

That's too easy! Thanks Doc.

Like homer would say,, Doh,,,,!!!!!

Thank you both!!

that is what i wanted to know.
...and who keeps a tape measure in their pocket at all times??

Ron Jeremy?

..and who keeps a tape measure in their pocket at all times??
Well that would be me, and Ron I guess

You two are almost twins, I know I don't look anything like the hedgehog...

and i as well. a 10ft stanley "mini tape" has resided in my pocket at all times for 40 some years or more. they get replaced when the 0-3" or so numbers wear off. [just say it and get it over with ! ]

We are twins where it counts.

I must admit you do have the best bacon though...

Chrysler engineers thought in fractions. The RB is 2 3/4, the B is 2 5/8.

R.