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Originally Posted by Kestas
Brian, MB specs the bearings at 0.01-0.02 mm axial play for proper installation, yet allows for 0.01-0.05 mm axial play as a check after use.
If I may take a stab at where this extra play comes from, it can be grease or grit that finds its way onto the mounting surface that hasn't been squeezed out or crushed down. Also, there are asperities on the surface that preclude a perfect mount. During use there is some flexing of the components and micromovement of the surfaces that act on these irregularities and increase play. Large amounts of it are called "fretting". This presents itself as polish with perhaps some brown discoloration on the mount surfaces. The brown is iron oxide products from the fretted surfaces.
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I'm aware of the specs. I like to work in inches. The limit is .0008" axial play during a proper installation.
I agree with all of your statements regarding where the extra play comes from. All of those possibilites will give a variable on the order of .0005" or so. None of them can be of significance to the point where an axial play of .005" would be realized.
So, the question remains. If the axial play increased to approximately .005", where did it come from? It's not from flexing of the components, micromovement of the surfaces, or fretting.