BN serial number tag missing

we have a Farmall BN with the serial number tag missing and it has a 123 engine in it instead of a 113 so IH must have replaced it at some point. So the numbers on the engine aren't accurate, what should we do to find the year of it. thanks the farmall people.

May not be many if it is an early model, but casting codes in the form of month*day*year will help, i.e. 1*8*I is Jan 8, 1939. R is 1948, letters are consecutive between I and R. Letters are cast into the surface of at least the major parts. The * resembles a screw head.

How did you determine that it's a 123? If it was built as a 123, it will have an engine serial number prefix of FCM, which indicates the 123s built for SuperCs and SuperA-1s. (Most regular Cs had this same prefix on a 113, as well). If original to your tractor, it will have either a prefix of FAA and a suffix of X7(for very early BNs, ser# 48350 and below) or a prefix of FABN for any higher number.

Either of those last two would indicate a motor that was built as a 113, with a 3" sleeve bore. A great many of those motors were later effectively made into 123s with the simple replacement with 3-1/8" sleeves, so if your determination that it's a 123 was made by measuring the bores . . . Depending on what you find for date casting codes on the rest of the tractor, I'd be guided (and maybe you already are and my question is moot!) by the serial number on the motor. If it has the right prefix and a serial number consistent with the date codes on the torque tube, transmission and final drives, there's a good chance it's the original motor, and the number will give you a more accurate idea of the date.

As far as the date codes, those on the chassis itself will often pre-date the actual assembly of the tractor by several months, and the various dated you find could cover a span of three to five months. My '47 BN, for example has some November dates with a P ('46) and some early Qs ('47) which would be consistent with the 1947 serial number. Dates, if any, on the front and rear wheels (not any wheels weights, which could have been added later) are often much closer to the actual production date.

it says c 123 on the block.

Well, that would be a pretty good sign, wouldn't it! LOL

That leaves you with the casting codes. The last real changes of any substance to the BN were made in mid-1941, right about serial #60,000. If your dates put it after that, there shouldn't be anything too exotic to finding chassis parts. For the motor, if it has a prefix of C-123, it could even have come from a 100,130, 200 or 230 or later. You might want to try to nail that down if you need to go hunting parts or specs for it.