Pump assembly

A pump assembly for an internal combustion engine comprising a pump housing (40), at least one pumping arrangement having a pumping plunger (56, 58) for pressurising fluid within a pump chamber; a drive shaft (46) carrying a cam (48) and a cam rider (50) which cooperates with the pumping arrangement to drive plunger movement along a plunger axis; and a plate (74; 174; 274; 374) coupled, on one side (74b), to the cam rider (50) and, on its other side (74a), to the housing (40) by coupling means (84, 86, 80, 82; 84, 180; 280, 286; 380, 480).The coupling means is arranged to constrain movement of the plate (74; 174; 274; 374) relative to the housing (40) in a first linear direction and to constrain movement of the cam rider (50) relative to the plate in a second linear direction, and to prevent angular movement of the cam rider (50) about its axis. Wear of the plunger, or of any intermediate component between the cam rider and the plunger, can be reduced as the cam rider is unable to tilt about its axis.