On Tue, 2 Jan 2007 18:47:21 -0000, "tg"
wrote:

I have to replace some bearings in a generator I have. I discovered they are a common size - 6302-2RSH. What I want to know is, do
bearings come in different grades or qualities? Or are they all the same? I want to replace these bearings with the best I can get.
Thanks for any pointers.

Bearings do come in different grades and qualities but most generators
use bearings made to ABEC-1 standards as high precision is not needed.
All that means is that the ID, OD and width fall within certain
tolerances but has nothing to do with surface finish, concentricity
etc. I would definitely stay away from Chinese - some are reasonably
good, some are real trash and you don't know which you may be getting
and the same holds true for India. Any bearing from a major
manufacturer (NTN, NSK, SKF, FAG, Fafnir etc) will suffice however,
NTN has been considered to be a top brand for electric motors for
years. In a DuPont comparison, NTN ranked highest in the world in
quality and adherence to tolerance but the differences are negligible
for all practical purposes. Sealing is another issue - most electric
motor (and generator) bearings are shielded. Cheapest and fairly good
at blocking dirt but doesn't do anything for water. Sealed is best but
a full contact seal creates friction and increases start up torque.
Your best bet for this application would be a non-contact seal such as
the LLB suffix on NTN. A sealed or shielded bearing is also "lubed for
life" so you really don't need to grease it - just run it until it
begins to fail. Most bearing failures are caused by over lubrication.
Also, most manufactures have gone to an "EM" designation for electric
motor bearings which means they have certain qualities preferred for
electric motor applications. This automatically includes C3 internal
clearance for a press fit on the shaft. If the bearing doesn't say EM
then you need to make sure it does say C3. Good luck with your
selection.