Low inertia rocker arm with lash adjuster and engine valve

An engine valvetrain including a pivotally mounted rocker arm engagable at one end with a movable valve stem member for actuating the same, engine camshaft cam actuated means in contact with another portion of the rocker arm for pivoting the rocker arm at times in response to engine camshaft rotation, and a hydraulic lash adjusting assembly wholly contained within the rocker arm to continually compensate for any gradual relative displacement between the parts of the valvetrain, the assembly including a high pressure enclosed fluid chamber connected to a low pressure fluid reservoir having a gas spring wholly contained therein, and with the chamber containing a piston, a spring biasing the piston against the cam actuated means, and a one-way ball type check valve connecting the chamber and reservoir unseatable to supply makeup fluid to the chamber and seatable to establish movement of the rocker arm essentially concurrent with movement of the piston by the cam actuated means, the chamber and reservoir being spaced on opposite sides of the rocker arm shaft to minimize the overall width and rotational moment of inertia of the valvetrain.