An improved cutter assembly for use with a header of an agricultural harvester is provided. The assembly includes a pair of oppositely directed knife blades or cutter bars and a center knife drive. A crank shaft drives both knife blades in linear reciprocating paths with no fore and aft movement. As a consequence, harmful fore and aft vibration is eliminated. The assembly is simple and durable in design, less susceptible to vibration-induced wear and tear, and comparatively simple to manufacture and repair.