Abstract: A trigger system for the ignition system of an internal combustion engine having a crankcase with a rotatable crankshaft includes an aluminum disk-shaped hub for connection to the crankshaft and rotatable therewith on the end opposite the flywheel of the engine. The hub has at least one weight formed into the hub and offset from its center of gravity for balancing and reducing vibration of the engine during operation. A plurality of magnets or other magnetically responsive elements are provided in openings in a flange extending around the periphery of the hub. A stationary sensor is mounted adjacent the hub for detecting impulses from the magnetically responsive elements as the hub rotates and utilizing the impulses to trigger the ignition system.