FUEL PUMP LUBRICATION

A high-pressure fuel pump assembly (200) for use in an internal combustion engine is disclosed. The fuel pump assembly (200) comprises a pumping plunger (201; 301) for pressurising fuel within a pump chamber (220) during a plunger pumping stroke, a rider member (206) co-operable with a drive, and an interface member (226; 326) for imparting drive from the rider member (206) to the pumping plunger (201; 301) to perform the plunger pumping stroke, the interface member having an interface side (236; 336). The interface member (226; 326) comprises fluid flow means (250, 252, 254; 350, 352, 354, 368, 370, 372) for providing a fluid flow path from the pump chamber (220) to the interface side (236; 336) of the interface member (226; 326) such that, in use, a hydrostatic lubricating fuel film is generated between the interface member (226) and the rider member (206) on pressurisation of fuel in the pump chamber (220).