Protected lubricant reservoir with pressure control for sealed bearing earth boring drill bit

A rotary cone rock bit, comprises a bit body including a plurality of legs extending therefrom, each of the legs having an outer surface that includes a leading surface and a trailing surface, a roller cone rotatably supported on each of the legs, a bearing system between each cone and the leg on which it is supported, and a lubricant reservoir in flui d communication with the bearing system. The reservoir can be provided with a wear resistant plug , if desired. In the present bit, the reservoir can be pressured-balanced with fluid in the bit plenum or the borehole annulus, or maintained at some desired differential with respect to either o f these. Alternatively, the reservoir can be formed inside the bit body, preferably by means of a canister, which can be provided with venting means as desired.