An improved lubrication system and method for an internal combustion engine that includes an inertia pump in a piston that reacts to the movement of the piston and conveys a predetermined measure of lubricating oil to the space between the piston and its adjacent cylinder wall immediately below the upper piston rings as the piston reaches top dead center of its stroke cycle. A first embodiment utilizes check valves to responsively open and close passages for the pump in order to control the injection of the proper amount of oil during each cycle. A second embodiment relies on a single moving plunger mass element to provide both the pumping and the valving functions of the inertia pump. A third embodiment utilizes throttle valves to control the injection of the proper amount of oil and allow for a spill path without additional passages. A fourth embodiment utilizes a throttle valve and a check valve in combination to provide secure pumping and a spill path for excess oil.