[mactec54]

cowanrg

Yes you need to support the drive pulley at the top, there is something wrong also with your 2 AC Bearings, you can only have ( 1 ) nut to do a preload, as you have just said,you have ( 2 ) may be the front/bottom nut, is & should be just a locking nut for the outer bearing race, this is not for doing any preload, it is to lock the bearing in place against the shoulder, which it has to do, you don't want this nut to loose in any way, your preload can only be from the nut on the spindle behind the top AC Bearing

You don't need the other parts that are not doing anything, now that you have modified it

[cowanrg]

cowanrg

Yes you need to support the drive pulley at the top, there is something wrong also with your 2 AC Bearings, you can only have ( 1 ) nut to do a preload, as you have just said,you have ( 2 ) may be the front/bottom nut, is & should be just a locking nut for the outer bearing race, this is not for doing any preload, it is to lock the bearing in place against the shoulder, which it has to do, you don't want this nut to loose in any way, your preload can only be from the nut on the spindle behind the top AC Bearing

You don't need the other parts that are not doing anything, now that you have modified it

I'm probably explaining it wrong, but you might be right. The bottom part doesn't necessarily add pre-load I guess, but the top certainly does. It's the same way everyone else has rebuilt their spindle. That part took me awhile to get right and get the right spacers and shims, but it runs VERY well. Before it would get really warm too and there was a lot of noise, but now it's very quiet and runs cool, even at 5k RPM.

What is the purpose of the top bearings in my current configuration? Sure, it supports the pulley, but how much force is being exerted on that pulley? Wouldn't it just be the force of the tension of the belt? The bottom half is fully supported by the AC bearings. I know it's just anecdotal, but I tried pulling on the top of the spindle where the pulley sits, and it's pretty damn stiff. I didn't put an indicator on it, but there's no detectable deflection.

If I do absolutely need some support up top, I'm trying to think of a way to use just the top bearing for support, with some sort of flanged insert. At the very least, the bottom bearing seems redundant in this case.