G main bearings: what do I have?

Len

Member
A few months ago, I bought a non running G from the grandson of what used to be the local dealer. When I got it running, I discovered that when started it rumbled for a few seconds while it was developing oil pressure. Since I suspected main bearings, a couple days ago I dropped the pan and found out that I could pry the flywheel up a very noticeable amount. So, I pulled rear bearing: top is 10A 12420 and has what I assume is date: 69. Bottom is a lot harder to read but is 10A 12425, followed by a number that I read as "30". I suspect that they are not a matched pair. I pulled the number 4 rod bearing and it is 10A9254 and dated 11- 72. Crank looks good, bearings look good although bottom main shows some wear. Do those numbers make any sense, and what size main bearings do I order?
I pulled up some of the online AGCO parts books and those don't match any numbers that I could find, and I didn't spot a way to match part numbers.
 
I dont find any numbers as well. Dates are commonly found on them. I had two different dates in my M5 which doesnt necessarily mean the time they were put in, just manufactured. If the crank has been ground it will be stamped on it somewhere. Maybe someone on here will be able to shed some more light on the numbers.
 
The 10A12420 is the replacement for a 10R954 STD rear main in a GVI diesel. I couldn't cross the others.
 
Thanks everybody.
Today it sunk in that without the insert in that main, I could slide the crank forward a ways and try to get in there with a caliper. Took several readings that pretty much agree 2.89" so it looks like rear journal is .020" undersize.
When I get a chance and have the rear main supported, I'll see what inserts are in the front two main bearings.
 
I rotated the crank and kept inspecting and can't spot any stamps. Where would you think stamp most likely?

Unmatched rear main bearing pair seem to point to the 30+ year old overhaul not done to normal standards.
 
It more than likely would be between a main and a rod journal on the casting. I looked my M5 over a couple times and didnt see it but then found it. I think mine was stamped R-010 M-010.
 

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