An improved rotary roller reamer

The invention relates to a roller assembly (20) including a roller pin (22) and a roller (24) arranged to be mounted on said roller pin, seal means (34a,34b) between the roller pin and the roller arranged to prevent leakage of a lubricant from a clearance between the roller pin and the roller. The roller pin includes a bore (22c) which acts as a lubricant reservoir and is arranged so that lubricant from the lubricant reservoir can flow into the clearance. The bore is further arranged to receive a stationary pressure equalisation means (36). The pressure equalisation means serves to substantially equalize the pressure of the lubricant in the clearance on the seal means with the pressure of drilling mud surrounding the roller during use of the roller assembly so as to prevent damage to or blow out of the seal means.