I did some work on the bearing of mine last night.
I don’t believe that the motor on mine has ever been open, as the glue holding the rubber covers over the two screws of the retaining tab look original, and after I bought it I was told it had been in the studio it was pulled out of its entire life.
The shaft was nicely oiled save the oil at the bottom by the thrust bearing which had turned in to a light grease. Shaft wear to looks to be minimal.
Now, I noticed a few things…
First, the bearing cap has a dimple where the ball sits. I’ve read that others believe this is due to the ball spinning during operation, but I don’t believe that to be the case. On mine the ball sits rather snugly in the bushing, snugly enough that there’s no way it can spin. If it were spinning, the damage to the cap would be far greater as the cap material is very soft, and there’s no evidence of any lubrication in the cap.
Second, there was very light abrasions to the tops of the motor coils. The thrust pad was in good shape, and there was no sign that this was caused by the top-hat rubbing the coils due to thrust pad wear or any other issue.
Third, the ‘thread lock’ on the bearing doesn’t look to be thread lock to me. It’s green in color, and judging by the amount of heat it took to free it, I believe it’s Loctite 680 retaining compound, or something very similar. BTW, if you heat it up enough you can unscrew it with a towel and your hand as retaining compound becomes very fluid under appropriate heat. I had to stop and heat mine twice to keep it fluid, but no tools were necessary.
Now, my first attempt at putting it back together I put the cap back on, threw a few drops of oil in and put the top-hat back on. My bearing is so tight that after 30 minutes with light pressure, it hadn’t settled at all.
In mass production having process that take exorbitant amounts of time to complete, having variables, or having situations where line workers have to interpret information and make decisions is simply not done. Therefore, I feel the more reasonable explanation for the ‘wear’ seen on the parts is simply due to how it was assembled:
1) The top-hat is placed in the bearing with the ball and cap absent. The magnet holds it snug against the motor coils, so movement and potential damage to the coils are minimized.
2) The motor is inverted, and 2-3 drops of oil are placed in the bottom of the bearing.
3) The ball bearing is placed at the opening of the bushing.
4) Retaining compound is generously applied to the threads, and the cap is threaded on and tightened hand-snug.
That’s it. The entire process takes a minute or two, explains all the witness marks on the parts, puts the ball bearing at the right depth in the bushing, assures proper lubrication at the bottom of the bearing and thrust bearing, and you don’t have to let parts settle for hours, hoping all the air was displaced.