bicycle bearings/ info please

hi all, spring is here, and on sunday it took my bicycle apart to grease the bearings. I had a few questions about them if anyone knows.
Are all bearings removable, or are they sealed on some bikes?
On my rear tire, there were two bearings that were loose, with no housing to hold the steel balls. Just a few supper thin spacers, and the nut. What is the purpose of this? Why are they loose? I actually had most of the balls there with a few missing, but I had no choice but to oil them, and leave them as were, with the few missing.

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Permalink Reply by Ron on April 6, 2009 at 4:52am

Hi Jill, loose bearings are generally better than the ones in the casing. You do need to replace all of them since some were missing. When bearings are missing the ones that remain have a tendency to become oval shaped. I have plenty if you need them. You also want to use grease instead of oil, as oil just runs out of the cups. Synthetic grease works best. Feel free to bring it to our space and disassemble it here. We can give you any other advice you might need also.
Ron

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Permalink Reply by krems81 on April 7, 2009 at 10:15pm

Front wheels take 10, 3/16" inch bearings on each side of the hub. Rear wheels take 9, 1/4" bearings on each side. A bike shop should be able to sell you some new ones for just a few dollars. Its best to use bearings from the same run, rather than taking a few from an old wheel. If you swipe them from another wheel, make sure they're shiny and in good shape, and take them all, not just a few, and replace them as a set. Also, Ron is right about grease.