- Small engines starters are either recoil or electric, though on rare occasions both systems are used. Your lawnmower, unless it is very large, probably employs a recoil starter. Equipment with higher horsepower motors, such as lawn tractors and snowblowers, may use electric starters.
- Pulling the starter rope of a small engine with a recoil starter causes the pulley containing the rope to spin rapidly. Centrifugal action causes a pawl within the pulley to extend outward and engage teeth on the interior of the flywheel hub linking the pulley and the flywheel. This action takes place within the first few inches of rope travel; the remainder of the rope pull spins the engine over and starts it. Pulling the rope also winds a spring under the pulley. Releasing the pull handle lets this spring turn the pulley in the reverse direction to rewind the rope. The pawl, which is designed to ratchet when the engine starts, is disengaged at the moment the rewinding starts.
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Electric start engines have a small electric motor, called a starter motor, mounted on the side of the engine. This motor has a device called a Bendix drive, mounted on the threaded output shaft. A Bendix drive is essentially a gear with a one-way clutch that engages only as long as power is applied to it. The starter motor drives the Bendix up the threads on the shaft to engage teeth on the perimeter of the flywheel, spinning the engine over. When the engine starts, the flywheel turns faster than the starter causing the one-way clutch to disengage. Shutting off the voltage to the starter motor allows the Bendix to drop back down the shaft threads away from the flywheel.
Twelve-volt electric start engines have an alternator and voltage regulator mounted under the flywheel to charge and maintain the battery. A few models of snowblowers do not use a 12-volt starter, employing instead a 110-volt motor that must be plugged in to a wall outlet for operation.
