Farmall A or B? Which is it?

Ok, here you go... Looks to me like its an A that had a B engine swapped in, but could possibly be an A with a B engine from the factory because the block and head are from 1945 and the tractor (tranny) was built in the middle of 1946. Maybe a left over engine that got stuck in an A? The seat is factory and mounted to the final drive. There's a big long weld on the front left between the engine and radiator... it angles down from front to back. There's also a weld half way around the top of the left rear housing where it bolts to the final drive. Here's the #'s...

Block: 2*14*O FAB 193113
Mag serial # 950769
Head: 2*28*O
seat bracket serial # 153885
Tranny: 5*2*P
LF wheel: 5*2*P

Lost my thought... the two welds both on the left side... wonder if maybe a tree fell on the tractor or it got turned over? the hood also has the extra hole on the right side for the starter tank, but the tractor doesn't have the tank or any extra levers/mounts for the shutters (also doesn't have those...) The fuel bowl also only has one inflow, but it could have been replaced I guess. The bracket that the starter lever goes through does have 3 holes in it... for shutters?

A and B engines are identical except the A engine will have a engine serial prefix of FAA, the B, FAB--there are NO differences. As to the tractor itself the A engine is offset to the left, the B engine is centered. A has WFE, B SF or NF, but could have been modified.

You mention a welded up crack in the housing where it bolts up to the left final drive. If you're describing a differential shaft housing that mirrors the one under the seat platform, then it should not look like an A at all, but either a B or BN. Repeating from the thread a page or two down, the diff shaft housings, bot the left and the one one the right, under the seat, are each 18" wide on a BN and 22" on a B.

That much is fact. The rest of this is speculation, which may be as far as you get unless you know the people who owned the tractor when all of this work was done on it. It's like trying to figure out what was originally what when you find a wide front under what is otherwise a B or BN, or a narrow front under what otherwise looks like an A.

With the dates and serial numbers both as far apart as they are between the motor and the rest of the tractor, and for other reasons, the idea about having an extra motor laying around the factory looking for a home doesn't really fly. A more typical span of dates between different castings would be on the order of three to five months, not fifteen. They would not have shipped a tractor with a dual-fuel hood over a gasoline motor. Also, if you look at the numbers, they would have had a chassis or some part of one laying around for a year or so waiting for a motor instead of the other way around -- highly unlikely I'd suspect. More likely they'd have simply skipped the number and gone on about production. (That's how the total number produced get apart from the last serial number-minus-500 formula on a given model or series.)

I don't know how the line was set up in Chicago or at what point in the process serial numbers were assigned and stamped on a given tractor and motor and matched up. If you look at the chassis plate, the model and serial numbers are usually stamped evenly, as if done with a machine. (The exception on the plates might be seen in the max rpms. I have one stamped very nicely. On my BN, it is obviously handstamped using one die for the "15" and a different die for the "40"). Motors all appear to be stamped by hand, with the characters all a little out of line in different directions and struck to different depths.

Far more likely your motor was replaced at some point for some reason. The repaired damage could have happened after that point and may even be likely. I'd hate to see the original motor if a welded up block and all the unknowns that go with that was a step up.

Not sure what to think of the damage at the rear. One scenario might be that they had some kind of weight in tow when they hit something with the left wheel or dropped it in a hole.

As far as the block, a lot of 113 blocks have a fairly small crack (not as big as you describe) in the area behind the carburetor, and they are usually attributed to freezing. It's possible yours is just an extreme cse of that. Another common repair is seen to the "ears" at the front of the motor where the front casting bolts up. This usually follows having dropped the front end of the tractor into a hole or ditch, stressing and breaking those ears. Not inconceivable that a crack from that kind of damage ran back along the side of the crankcase.

Best I can offer out of all the unknowns is to assume you have a replacement motor, and to find the model number on that chassis serial number plate and see how that matches up to how your rear end is configured, wide (B), narrow (BN), or offset (A).

The tractor itself is undoubtedly configured as an A, that was never in question. The left side is short, the weld runs from about 10:00 to 2:00 on the housing (diff) where it attaches to the tranny. The crack isn't on the block of the engine at all. It sits right under the lower radiator hose... the axle mounts to it... its right in the same area as the u-bolt that limits axle travel. The weld is about 1/2" wide and around 5 or 6 inches long there. I also just thought about it, but the light bracket appears to have been struck from above because the bracket/bar is also welded in place because it appears the base was damaged where the set screw comes down into it. The radiator drain plug looks like the handle/ears on it were knocked off as well. No engine cracks... the engine serial number was definately hand stamped because its all out of wack. What doesn't make sense is that the casting date on the block and head says 1945(O), but the serial number looks like its a 47 or something if you use guy fay's info. If the tractor itself is a 1946 with a 158*** serial number, why the heck is the block a 1945 with a 190*** whatever serial number??? I can't find any FAB specific serial number dating info... Guy fay's book says to refer to the FAA serial numbers...

As and Bs shared the same serial number sequence. 501 might be an A, and 502 might be a B, for example.

Okay. We've benn fliundering through a nomenclature problem, and you cleared up quite a lot for both of us. That big casting on the left rear that you're calling a diff housing is more actually and more usually called a final drive. Since the diff is in the aft section of the tranny case, there is no separate diff housing. The final drive setup a)allowed the tractor to be run on smaller tires but lifted it up to clear rows for cultivating and b) made for a handy opportunity to install a final gear reduction (thus, final drive), with the small bull pinion on the outer end of the diff shaft turning the big bull gear on the axle. Onthe taller tractors (H, M and later the C) that reduction was made in the tranny case.

What I've been referring to as the diff shaft housing others call the diff housing (So you understand all the confusion I've been suffering, others call it the axle housing, which ain't perzackily right, either!), but is simply the casting between the tranny case and the final drive, that encloses the shaft running out of the diff to the final drive. Yours has one on the right but not on the left. On yours it is the final drive that bolts up directly to the left side of the tranny case, the shaft being much shorter and not needing the extended housing that is on the right.

And my apologies. I mis-read something and thought it was the crankcase that was patched, but it's most definitely the front casting. Sounds almost like it was hit from the side or the left side dropped into a ditch at some point. Such an accident might also have busted the ears off the motor where the front casting bolts up like I described earlier. Most often, the front casting would survive intact but the ears on the motor (the weak point in the connection) be busted. If whatever happened was forceful enough to break that casting, it shouldn't surprise me if the damage to the crankcase extended well beyond the ears, which MIGHT explain them putting in a replacement motor.

As for the motor, look closer at the casting date on that block. I'm suspecting your O is a Q, which would be more like right for your '47 serial number. The block on my 47 BN (#1900##) was cast in mid-December of '46 (P), so it would follow that yours (#1931##) would have followed a couple of months or so later, and have a date of 2-14-Q. My tranny case on that same tractor is dated 2-10-Q, but you have to look real hard to see that it's a Q not an O. IH's Q didn't have much more than a little nub more near the bottom than the corner to distinguish it from an O, and it doesn't take much paint or rust to obscure it. Dollars to donuts that's your answer there.

mkirsch addresssed the serial number sequence. There was only one series of numbers used for As and Bs starting at 501. All that changed (with the exception of the very early production) was the prefix to the serial number on the plate. Your 158### should have a prefix in front of it on the plate. By that time the model numbers were distinct, and A would have a prefix FAA, FAB for Bs and FABN for BNs. I don't know what shape your plate is in or whether you can still distinguish the various blocks on it, but immediately to the left and a little away from the FAX158### , there would have been a block for the Model, and would have been stamped A, B or BN. If it's an original plate, it's there.