greasing closed bearings on the outside Assume I have a couple of closed bearings on some pivots on my bicycle.



These bearings:


are fitted on a housing
have an axle going through them
are tightened by bolts which also have cups to "protect" the black plastic part of the closed bearing


My question is, would you use grease between that black plastic part and the axle cup to protect the bearing from water and dust? I'm talking about a lot of waterproof grease which upon bolt tightening will overflow. Of course I will wipe out any excess after tightening.

I'm asking because even if the bearings are of high quality, I will sometimes find that dust or other small particles have entered its inside area making the bearing lose its smoothness and eventually making it wear faster. So, could that extra grease on the outside act as protection?

Edit: This question doesn't regard greasing inside the bearing. I'm asking whether puting grease on the bearing, covering the metal and the black part, will prevent water and dust from entering.
Generally speaking, that style of bearing ("sealed cartridge bearing") is "permanently lubricated".  You do not lubricate them and you replace the entire assembly if anything goes wrong with them.  

A few people have claimed success by gently prying back the flexible gasket and injecting grease with a syringe, but these claims are subject to legitimate skepticism.

Note that the inside diameter and the outside diameter are not supposed to move relative to the external parts that hold them.  If they are slipping it indicates that the "holders" are not tight enough or the bearing is failing and needs to be replaced.