Thoroughly clean out the bearing with either motor spray or nitro wash. RPM makes a bearing blaster
that makes the process very easy, or you can also use a jewerly cleaner device (Indi Sparkle
) filled with cleaner. These two items will make the cleaning very easy, but you can also just use a plastic bag or small cup filled with cleaner.
Once the bearings have been cleaned, spin them to "feel" if there is any grit left. If there is, repeat the process until all the grit is gone. Once there is no grit, lube the bearings with thin bearing oil and re-install.
After a year of use, you may find that some or all of the bearings may need to be replaced.