ROTARY ROLLER REAMER

A bore hole rotary reamer (1) includes a body (2) having cutters (4) contain ed in respective recesses (3) formed in the body (2). Each cutter (4) is rotatably mounted by one or more respective spindles (5). A bearing region (10) is formed by an inner bearing surface (11) rotatable on an outer surfac e of the spindle (5). At least one annular seal (12) about the spindle (5) prevents ingress of contaminant to the bearing region (10). A circumferentia l void (13) is formed between the inner bearing surface (11) and the outer bearing surface of the spindle (5) adjacent the seal (12). At least one passageway (17) extends in an axial direction of the spindle (5) to the circumferential void (13) and a piston (19) movable in the passageway (17) i n response to supply of pressure to an outer side (19a) of the piston (19) fro m the environment which surrounds the reamer (1). The piston (19) transfers pressure to fluid in the cylindrical passage (17) on an inner side of the piston (19) to supply pressure to the circumferential void (13) and thereby to the seal (12) that is substantially determined by the pressure of the environment surrounding the reamer (1).