Originally Posted by rcoolbaugh
Right .... I did the measurement before I removed the original bearing and calculated the correct shim thickness. I wanted to verify that the new bearing was the same thickness which would make my calculation still valid.
I did measure both inner and outer races on both bearings. The bearings seem to be very consistent.
But did you check the NEW bearing with the dial micrometer using the same technique you used to check the original bearing?
If not, you are making assumptions that may not be true.
What you fail to measure when you just measure race width is the axial play that is inherent in the bearing. That is a function of the grooves in the bearing and the balls, and the size of the races. The size (radius) of the races changes; when you install the bearing on the crownwheel assembly hub, you stretch it. When you press the outer race into the FD cover, you shrink it. These changes influence the axial movement of the inner race with respect to the outer race.
This is from the post made by a Niel, a mechanical engineer and he is making an important point: "The race widths by themselves will be very accurate. It is the internal axial clearances that will vary - especially if the inner race is pressed or shrunk onto a shaft.."
Just comparing the width of the races of old and new bearings you are not measuring the differences between the bearings. The bearings are probably pretty close to eachother, but from what you measured, you don't really know.
The right way to do it is to put the NEW bearing on the crownwheel assembly and do the measurements using the dial indicator method. Measuring the old one is interesting, academic, and gives us an indication as to how BMW set it up. But I wouldn't consider that measurement a reliable indicator of how to shim a different bearing. I wouldn't rebuild a drive without actually measuring the new bearing for preload. If I understand you correctly, I think you missed an opportunity to measure the new bearing.
Your set up may be close, or it may be dead on, but you don't really know.
If that were my drive, I'd take it apart again and measure the new bearing.