According to your request, your bearing is calculated as follows:

Update:31-05-2019
Summary:

Since you did not give the temperature distribution (ax […]

Since you did not give the temperature distribution (axis, bearing chamber), I only calculated the tolerance effect. Even so, since you did not give the tolerance of the bearing chamber, my calculation is only assuming the bearing chamber H7.

If it is the shaft diameter of n6, if the bearing of 6324/C3 is selected, the internal residual clearance is -0.005 to 0.049. If the fit is changed to m6, the remaining play is: 0.0003 to 0.057. As you can see from here, it's not that you need to choose the C4 problem, but you need to revisit your tolerances.

In addition, you said that to make room for thermal expansion, I think this statement needs to be considered a bit. Because, in fact, the so-called thermal expansion space, inside the bearing, the biggest impact is the clearance. With the right choice, the clearance is right, naturally, do not leave it alone.

The last general recommendation: general operating conditions for industrial motors. It is recommended to use C3 clearance (except for small motors). The tolerance fit is selected according to the manual unless there is a special change in the temperature load. (I believe the manual, the numbers in it are calculated.) Even in my personal work, the gap calculation is only done when there are special requirements for temperature or operating conditions. In general, choose directly according to the manual. (To be honest, I used to calculate it in the past, but found that many cases have been a big circle, and I still go back to the manual data. So, at this point, I believe in the manual. Of course, it is still the sentence, special case manual Not applicable)

After a motor with large vibration is disassembled, the grease in the bearing becomes silver-gray (originally milky white). What is the problem? Is the color change of the bearing grease normal? What color is normal? To what extent is normal. Some bearing greases also change color, from milky white to brown, and the discolored parts are around the rolling elements. What is the reason? If it becomes silvery, it is tight, the clearance is small, and the friction is large. Caused, but the same bearing has the phenomenon of running the outer ring. Why is this?