Recoil start

Starting a Lazair II ultralight aircraft's JPX PUL 425 engine, equipped with a recoil starter.

Recoil start (also called manual start, pull start or rewind start) is a method of starting an internal combustion engine, usually on small machines, such as lawn mowers, chainsaws, ultralight aircraft, small outboard motors and portable engine-generators. Recoil start is also used on some small vehicles such as small go-karts, minibikes, and small ATVs.

Modern version

The starter mechanism comprises a rope, with a grip at the end, moulded rope reels and a spring. The rope is coiled within a reel which is held under spring tension within an outer reel. This reel assembly is in contact with one end of the crankshaft through a ratcheting mechanism (specifically, a freewheel clutch). When the rope's grip is pulled, the rope uncoils, tensions the spring, engages the clutch and turns the crankshaft, spinning it to crank or start the engine before the end of the pull stroke. After the end of the pull is reached, the spring operated reel^[1] retracts the rope, either to store it, or to prepare it for another attempt to start and disengages the clutch hence the term "re-coil starter". If the reel were directly connected to the crank and lacked the freewheel mechanism, once the rope reached its end, the spinning crankshaft would keep turning the reel, which would violently recoil the rope in the opposite direction until it reached its end, where it would likely jam and stall the engine.

Old version

There is an older, simpler version of pull starter that has a reel directly connected to the crankshaft, and a rope that is not connected to the reel. The rope is wound around the reel and pulled, starting the engine, but once the end of the pull is reached, it comes free, leaving a loose rope in the person's hand. If the engine fails to start on the first pull, the operator has to re-wind it by hand. This is also done when the engine is shut down to prepare it for the next start (this is technically not a recoil starter, since it doesn't re-coil the rope; both are actually forms of pull starter).

Easy start feature

Most modern engines have an easy start feature where one of the engine valves is held open by a special cam while the rope is being pulled, avoiding the need to overcome compression. This cam is deactivated at the end of the "pull" so that the engine can fire and run by itself.

References