Re: 21 Stud 37mod
 

Annoyingly Ford called both 81A blocks. The Green Book lists the 2.4 inch main version as 81A-6010-A for 1938 only and the 2.5 inch main version as 81A-6010-B for 39-42*.

*really annoyingly Ford apparently didn't change part numbers when the following three changes were made around the 40-41 model year change over to the blocks: "raised" intake surface (actually shrunk outside the gasket area), elimination of the core plugs in the oil pan rail, and sides of the block curved up to the exhaust ports.

I only know this stuff since I really like 38 Fords and trying to figure out how to make a correct looking 24 stud motor takes a bit of reading. I appreciate your experience and willingness to share, please don't take my clarifications as anything bad or mean.

Re: 21 Stud 37mod
 

Well it's hard to teach an old dog new tricks, but i've been known to have a very hi "stupid factor". Don't worry about correcting me or anyone else here if they make a mistake, Facts are facts. I don't know very much about all the models of early ford parts as I seldom use them. as for the early 91a crank, it was popular back in the day when we thought things like that were important. The only people that don't make mistakes , are people that don't do anything.
Gramps

Re: 21 Stud 37mod
 

How does one tell a 1938 block with out tearing into it.

Re: 21 Stud 37mod
 

How does one tell a 1938 block with out tearing into it.

Look at the length of the crankshaft snout

Re: 21 Stud 37mod
 

Just a hunch, but the three changes listed do not alter compatibility with any other parts, so there is no need to make the distinction.

Mart.