Crown wheel bearing arrived from Chicago BMW in just a few days, they must have had one in stock.
Credits to Dman who developed the technique I am using.
To avoid any pressure on the bearing balls and races during assembly, I heated the bearing in the oven (I used 350 degrees F) and chilled the crown wheel in the freezer. The bearing dropped onto the crown wheel without any pressure at all, gravity does it. I just made sure the bearing was fully seated on the crown wheel before the temps started to equalize. (Improper assembly technique where excess pressure is applied to the balls and races causing galling is one theory as to why these bearings are failing, so treating the bearing kindly during assembly was important to me.)
(Note: I am doing nothing to check crown wheel gear to pinion gear backlash. I inspected the gear teeth, taper roller bearing, checked the input pinion shaft for smooth rotation and decided all was okay. My procedure described here is only about installing a replacement crown wheel bearing and measuring for proper pre-load shimming.)
Another theory of final drive failure causation is improper preload, so I wanted to be very careful in measuring for preload shim thickness.
With the crown wheel/crown wheel bearing assembly placed into the drive housing, I heated the housing cover in the oven to about 170F. (BMW manual says 140F but my wife's oven doesn't set that low
). The heated cover was quickly bolted in place on the drive housing. A dial micrometer set up. Two bolts placed into the holes in the crown wheel where the brake rotor normally bolts on. These are used to pull the crown wheel assembly up. The amount of movement is the amount of shim distance without pre-load added. NOTE: If the drive cover is too hot the crown wheel assembly moves easily and the shim distance measured will be GREATER than measured after the drive cover is cooler. POINT BEING: TEMP DIFFERENTIAL OF THE COVER DOES ALTER THE MEASURED SHIM DISTANCE. If you use a heat gun to heat the cover and have no ability to measure the temp you could make it too hot, the assembly will move up and down easily and the shim distance measured will be inaccurately large.
I experimented with a very hot cover (350F) and as the cover cooled, it became necessary to use increased force to pull the crown wheel assembly up (I used a couple of tire irons) and firm pressure was required to push the assembly back down. On this particular final drive, as the temp cooled the shim distance became a very repeatable 0.011 inch (0.28mm).
I used a heat gun to reheat the drive cover for easy removal and repeated the process several times. I removed and reinstalled the cover three times and made multiple measurements each time. As the cover cools, moving the crown wheel assembly up and down becomes increasingly difficult, but as it does, the measurements stabilize and become very consistent.
BMW Service manual states pre-load is 0.05-0.10mm. My observed shim space without preload was 0.28mm. Adding preload gives a shim range of 0.33-0.38mm.
Shims (spacer rings) are available from 0.10mm to 1.70mm thickness at 0.10 intervals, except there is one shim that is 0.15mm thick. That explains why two shims were in this drive! Rather than having twice as many shims available, BMW expects you to use a combination of shims if you want multiple of 0.05mm. So if you want a 0.35mm shim, you need to use a 0.20mm + a 0.15mm shim.
My plan is to complete the rebuild of this drive and then put it in a shipping box with tools ready to go. At some point when I am putting on a new rear tire, I'll change out my final drive and put a few thousand on this one just to "break it in". (BTW the final drive on my bike was rebuilt by me about 30K miles ago as a preemptive measure and it is going strong.)
Hope this helps someone else who is interested in rebuilding their drive.
Also: I'd like to compare this technique with that used by BMW using their special tool. I think I could make such a tool from trashed final drive cover. Anyone have a really trashed final drive cover they want to part with?