Yours is a good question, but very few will probably have worked at this level. Here are some suggestions:
BMW seem to use bearing color coding for their cars (M3) so Google to find out their logic.
From past experience rebuilding engines, manufacturers forge and grind their cranks, but to get the most bearing mileage they select bearing shells to fit the tolerance range of each batch of cranks made. That is on a new bike build. So you measure the crank journal size then find out what crank journal size fits the tolerance range for each of the BMW parts. You need that information. Do not think you can compensate for journal wear by selecting the next undersize shell. Crank journals wear oval and not at the extreme edges so you need to make several measurements on your journals. If you are replacing with the same and not regrinding, you should take the largest of your crank journal measurements NOT the smallest!
If a crank jounal is damaged, then it can be re-ground (made slightly smaller) and replacement undersize bearing shells may be sold in 10 or 20 thou step sizes. In a good precision workshop, a crank can be ground to a precise undersize, so you do not need to tolerance select new bearing shells.
You should try and find out what shell sizes those part numbers correspond to. Ask your dealer to email the BMW mothership and tell us the answers. BMW are pretty good at numbering their parts. If you cannot find paint marking on the crank. then see if they have marked the shells with a part code other than paint. You should micrometer each crank journal anyway to check the sizes are consistent and all will fit one of their shell size tolerance range. With an internal micrometer (or bore gauge) you should be able to mount a pair of shells in each con rod and measure the internal shell size of your worn shells.
In the BMW shop manual they use Plastiguage to check journal/shell wear which should be in the range 30-66 microns with a wear limit of 130 microns. They say that regrind stages are '0' and '1' with the crank pins carrying paint spots. If there are no paint spots they say that regrind is at base stage '0' implying, you can go one more, but journals must be hardened and finished afterwards!
Do NOT treat this link as relevant, but it gives you some ideas:
red - 59.980-59.990
blue - 59.971-59.980
yellow - 59.984-59.990
green - 59.977-59.983
white - 59.971-59.976
If you look at those size ranges they are all undersize and less than 60.00mm. a micron is 1/1000 mm.
In the above table for the car, Red is 10-20 micron undersize, Blue 20-29 micron, yellow 10 to 16, green 17-23 and white 24-29 microns.
None of the above are regrind undersizes which would be 254 microns each undersize step.
In the above car example I suggest the BMW shell color coding is a way of grading their assembled cranks to take account of crank journal manufacturing tolerances.
An important point is I do not see undersize shells listed, should you find your crank needs to be reground. However, these may be available from a 3rd party supplier since you would not expect BMW to list shell sizes for a reworked motor.
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