Thono, I typed this up and just prior to posting read Dan`s contribution so thought to bin this, which may be all it is worth.... (-: BUT I thought to post it anyway..
as I have typed before I have not even sat in a M3W, let alone put a spanner to one, so I could be typing NONSENSE. I was passing time and wandered into the M3W section and read your post, and until someone who knows what they are typing about comes along I thought to share my thinking as I have nothing better to do at the moment.. (-:
I know not the entire set-up of the BB though the taper bearing assembly seems not a lot different to a wheel bearing set up where ideally there is no real pressure exerted on the bearings during assembly other than to endure they are fully seated with no play between them.
Overtightening the nut creates extra loading on the rollers and bearing faces, and would seem less than ideal, to avoid this there can be a tab washer or castellated nut and split pin involved to hold the nut from spinning and altering the initial adjustment once set..?
The method I have used in the past when replacing tapered WHEEL bearings, was to tighten the nut up enough to be sure that the new bearings had seated properly which is important, as an incorrectly seated bearing may in use end up seating it`s self and altering the vital clearance once in service...
Once satisfied the bearing are seated the nut is loosened back until play is evident then re tightened till no play was felt in the bearings at which stage the tab washer would be bent over a flat on the retaining nut. Or in the case of a castellated nut the split pin would be used to stop it from rotating, there have been other methods used over the years.
Admittedly it is relatively simple to check if the play has been taken up in a taper bearing set-up on a road wheel, as you can just grab the top and bottom of the wheel at the same time, pushing on one hand while pulling on the other then in reversing that process you then can feel if there is ANY play in the bearing. After adjustment I always checked that the hub was free to spin freely with zero resistance felt.
Looking at the pic of the BB bearing set up you posted it may be that a dial gauge is best used to determine if all the play is adjusted out of the assembly. Having typed that an overtightened nut would show no reading on the dial gauge, thus care must be taken NOT to overtighten the nut and some process of determining the bearings are free to rotate as opposed to being overloaded which would cause advanced wear over heating and rumbling prior to total bearing failure...? Given that there is a helical gear meshing with another, I suspect there may be a degree of play required in that assembly, and if that is the case then that play can perhaps be utilised to help determine that the the shaft can rotate freely to some extent...?
Whether any or none of this ramble is of any use whatsoever, I know NOT, just thought to give you something to think about Thono, while you wait till someone who really knows what they are typing about hopefully jumps in.
