HIGH-PRESSURE FUEL PUMP

A fuel pump includes a plunger which reciprocates within a bore of a housing. The plunger extends from a first end proximal to a pumping chamber to a second end distal from the pumping chamber and includes a sealing ring groove between the first end and the second end. The sealing ring groove extends from an upper shoulder proximal to the first end to a lower shoulder distal from the first end and are separated by a first distance. A sealing ring is located within the sealing ring groove and engages the bore in an interference fit. A diametric clearance greater than 12 microns and less than 30 microns is provided between the plunger and the bore such that the diametric clearance extends between the sealing ring groove and the first end for a second distance which is at least four times the first distance.