PUMP UNIT FOR FEEDING FUEL TO AN INTERNAL-COMBUSTION ENGINE

A pump unit for feeding fuel, in particular diesel fuel, to an internal-combustion engine; the pump unit comprising a head () inside which a cylinder () is formed along an axis; a pumping piston () housed inside the cylinder and comprising a head portion () inside the cylinder and an opposite foot portion () projecting outside the cylinder; wherein the piston is slidable inside the cylinder in a reciprocating manner between a first position and a second position where the foot projects from the cylinder by a greater or smaller amount respectively; and wherein the outer surface of the piston comprises a portion () with a surface finish so as to have less friction and a greater lubricant-retaining capacity than the remainder of the outer surface of the piston; the portion extending along the axis between the head of the piston and a first intermediate point () in the first position of the piston, the first intermediate point being inside the cylinder.