||The cylinder on the axle of this engine is a
centrifugal clutch. The axle can spin freely up to about 600 RPM.
Above that, weights push out against the cylinder and the chain sprocket
begins to spin.
These are the simplest and least expensive form of clutch. If
you're going to purchase one part, this is probably the one to purchase.
Make sure that it fits the axle of your engine and the sprocket's teeth
spacing matches your chain. They're about $30.
|This clutch is from a lawn mower. A belt
drives a shaft which turns the chain sprocket. In this case the shaft
moves forward and backward to loosen and tighten the belt. The white
pipe going diagonally in front of the engine is dropped by the driver to
engage the engine.
This particular clutch tended to engage suddenly, with
a low gear ratio, which resulted in much smoke and tire wear.
||You can make a clutch similar to
the above with an axle that doesn't move. Instead an idler pulley
tightens the belt when the operator lifts on a lever. A big advantage
of this is that if one of the pulleys is a cone pulley then it is feasible
to have gears. A cone pulley is a pulley with three to five grooves,
each with a different circumference. The driver wiggles the
idler until the belt is in the smallest groove. This is first gear.
When the go-kart is up to about 10 mph the driver eases the idler and
wiggles it until the belt slips onto the second groove.
The idler pulley can be simply a belt pulley spinning on a bolt, though
bearings are preferable.
||The world's simplest clutch is to
not have one. The wheel is directly tied to the engine with a chain.
The rear axle of the go-kart is put up on blocks while it is started.
Once it's running you shove it off the blocks. While not ideal this
can work, particularly if headed down hill.
||It's often hard to keep the chain
A relatively easy solution to this is to mount the engine on a platform
which is bolted on only one side of the go-kart so that it can move backward
and forward a few inches on the chain side.
Then a piece of wire such as coat hanger from the front of the go-kart to
the engine mount and back. A stick between the two pieces of wire is
twisted around to tighten the wire and pull the engine mount forward.
This is a technique cowboys use to tighten fences.
||On this go-kart we had continual
problems with the chain falling off. When it accelerated the front
portion of the chain vibrated and fell off. We tried using various
idler pulleys including the derailleur from a bicycle. The boys came
up with this final solution, a simple piece of plastic tubing that
reduces chain vibration.