Abstract: Conventional tappet retainer assemblies for a fuel injection pump typically include a blind radial passage formed in a tappet. Only one opening in the passage is available for inserting and removing a ball bearing or spring and stop pin which must be held in place before the tappet is inserted in a housing bore. In such an arrangement, the ball bearing or compressed spring and stop pin are prone to pop or fall out before the passage opening is closed by an internal wall of the housing bore. The present invention provides an improved tappet retainer assembly which includes a housing, a tappet, a stop device, and a biasing device. The tappet includes an internal passage which allows the stop device and biasing device to be communicated to their final assembled position in the internal passage while the tappet is already inserted in a bore of the housing.