[suicideneil]

Abec 3 or better bearings should be fine, all you really need to do/ can do to maintain the MMM motors is just clean the bearings with a drop of 3in1 oil or wd40 to flush out dirt every now and then. Basically just keep it lubed- if you notice the bearings are rough, then you might want to concider changing them, otherwise, its pretty much maintainance free...