A name brand bearing is all you need. If you're OK with slightly shorter life even the cheapest bearing will be OK. Ball bearings in electric motors have a relatively easy life, little vibration, little heat, low RPM (relative to their size), and until the inevitable crash or prop strike, low load. Motors running spur gear drives do put load on the output bearing and often pay for it in life. I think the biggest difference between 1$ bearings and name brand is the risk of premature failure, essentially DOA junk.

The only difference in bearing quality which you may notice is noise, but even then in small sizes it's merely a little hiss. In a model, the prop and switching noise far exceeds bearing noise.

I can't think of a reason to justify hybrids for a typical electric motor.

I agree, chrome steel bearings are fine. I would stay in the meaty part of the price point and not cheap out too much. I use hybrid ceramic but just for the ego. As small as they are they don't cost all that much but provide a great mental boost. C-3, C-4 fit is standard, if you go to C-2 you might get binding unless the bearing pockets are perfectly aligned and the bearings are perfectly installed and they stay that way. They're really more for precision instuments than running motors. You can take the motor apart and look for scuffing but I suspect the noise is just prop flex/turbulance.

MM

While we are on the subject of 3515's I have one plane that makes the normal quick spin in the rotation direction when the esc arms and another one that just grunts and moves the prop about 1/2".  Both spin up normally and fly fine.  Is that the motor or something in the ESC.  It is almost like it is getting spin up commands in both directions at the same time!

Anybody else experienced this?  Spin Pro ESC.

Ken

It would be the ESC.  Need to set the throttle end points on the one that just burps a 1/2". It's idle end point (OFF end point) is set too high.  Your ESC or timer instructions should have a how to on this.

I solved the noise problem for now.  I removed the BA 3515/580kv and replaced it with a spare BA 2826/690kv.  It is now very quiet in flight. 

The rear collet on the 5mm shaft was a bit loose on the 3515.  This was allowing the can on the motor to move fore/aft a fair amount.  That was the likely the culprit for the unpleasant grinding noises in the turns.  I will disassemble the motor to see if there are any scuffing marks on the magnets or stator and I'll possibly replace the bearings while I'm at it.  Compared directly, the new 2826 has almost zero fore/aft free-play.  I do like that 2826 uses 3 bearings.  Seems like 3 bearings would support everything slightly better in a rear-mount, 2-blade setup like mine.  There is a lot of cantilevered forces happening.

To satisfy my curiosity, I pulled the Castle ESC data log for my two test flights with the 2826 motor.  The log shows this motor only pulled 442 watts and 21.2 amps at peak with the 12x6e APC at 9250'ish rpm.  The data indicated that I used around 1380mAh of the (P26a) 6S-2600 li-ion battery, (which was only charged up to 4.15v per cell.)  I was relieved to see that voltage sag is not much of a concern with this combo, as the voltage was only pulled down to a few low blips of 3.3v per cell during the overhead-8 and clover.  It is reassuring to know that using the 690KV motor, there is plenty battery voltage headroom on tap, and I am nowhere near the 2.7v sag prevention cutoff setting that many discuss.   When I checked the battery a few minutes after landing, I saw ~3.6v per cell on my meter. 

Glad to find (but not surprised) that the BA 2826/690kv is also a pretty happy combo in this plane.  The 2826 tugs this 64oz plane along with just as much authority as the 3515 it replaced.  5.3 lap, using 69ft .018" lines.  I'll just fly the Sultan in this configuration for a while and use the repaired 3515 in something else.