Does anyone know what the A and B letters that are cast into the block of an OM603 96X engine mean ?

We see a lot of these engines in our workshop for remanufacture and I've noticed that sometimes the pointer/arrow points to the A and sometimes to the B but I have no idea why.

I was asked this question the other day by an apprentice and I felt I really should have been able to give him an answer, but it has me stumped.

Anyone have an idea ?

The same markings are on many different MB engine block castings. I am not sure exactly, but I believe it is either a casting line or shift indicator. Together with the other casting date/etc. marks it would tell production which group/lot the block is from.

Yours is a bit blurry/sand wash out, but the A/B arrow is actually a pointer screwed onto the sand mold master pattern that can be flipped between the two positions (with a pin to keep it pointed right) . Below you can see the the same from a 1967 M108 block.

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Thank you for the reply. Your explanation is entirely plausible. I can see exactly how and why that would work at the casting foundry.
I'm going to suggest as much to the apprentice that asked the question.
Thanks again for your time.