Scooter Clutches, Transmissions, Chains, and Friction Drives
decisions you make here will determine the complexity of your
future gasscooter repairs and gas scooter maintenance. We
take the mystery out of gas scooter drives.
Next to brakes, the drive mechanism of your gas scooter is the second most
important decision you will make. Let's start with the basics. There
needs to be a means to get the output of the gas scooter engine to the wheel of the scooter
to make it move.
Direct Drive Gas
Some gas powered scooters use a means call
direct drive. Direct drive
is by far the simplest but has some major drawbacks. Direct drive simply
connects the wheel of the gas powered scooter directly to the out put
shaft of the engine typically via a chain. This means that the gas scooter will be moving
whenever the engine is running. So if you came to a stop sign and stopped,
the engine would also totally stop. To restart it, you would push the gas
powered scooter several feet which would restart the engine and cause the
scooter to take off again. Not a great configuration for children who
would be more apt to simply ride through the intersection if they thought it was
clear, rather than hop off of the gas scooter and have to restart it.
To avoid this scenario, there is a device called a centrifugal clutch
(pictured below front and back)
is the most common clutch used for gas powered scooters.
The clutch consists of three parts:
An outer drum (has the holes in it) that turns freely on a
bronze sleeve bearing - This drum includes a sprocket that
engages the chain. When the drum turns, the chain turns.
A center shaft attached directly to the engine's crankshaft -
engine is turning, so is the shaft.
A pair of cylindrical clutch weights
attached to the center shaft (shown installed to the right, and loose to the
with a spring that keeps them retracted against the shaft
The center shaft and weights spin as one. If they are spinning slowly enough,
the weights are held against the shaft by the spring. If the engine spins fast
enough, however, the centrifugal force on the weights overcomes the force
being applied by the spring, and the weights are slung outward. They come in
contact with the inside of the drum and the drum starts to spin. The drum,
weights and center shaft become a single spinning unit because of the friction
between the weights and the drum. Once the drum starts turning, so does the
chain and the gas scooter moves forward.
There are several advantages to a centrifugal clutch:
It is automatic. (In a car with a manual transmission, you need a clutch
pedal. A centrifugal clutch doesn't.)
It slips automatically to avoid stalling the engine. (In a car, the driver
must slip the clutch.)
Once the engine is spinning fast enough, there is no slip in the clutch.
It is very durable.
With such a
clutch, the engine can be safely started and will idle (run slowly) indefinitely
until the engine is sped up via the hand throttle. This allows for smooth
acceleration from a stop, and allows the gas scooter to stop without the engine
always shutting down.
Gas Scooter Gearboxes
Gearboxes are used to convert the relatively
high speed of the engine shaft
into a lower speed which can then be connected to the driven wheel.
Gearboxes typically will have a
5:1 gear ratio, which means if the engine shaft
is turning 5000 revolutions in one minute (RPM) then the output shaft of the
gearbox will only turn at 1000 revolutions per minute or RPM. This
reduction gives the gas powered scooter the power it needs to climb inclines.
Gas scooter gearboxes are a fixed ratio. This means, unlike a car there
are no gears to be shifted either automatically or manually. The
manufacturer of the scooter tries to find a ratio that will match up with the
size of the engine to provide good climbing ability with a reasonable top
speed. Go karts and snowmobiles, due to their larger size incorporate a
device called a torque converter which provided a variable ratio. As we
will see in the discussion below around chain drives, there are still methods to
alter the top speed or power of a gas scooter without changing out the
gearbox. Gear boxes contain gear oil which should be changed out every
year. There is a small drain plug (appears as gold nut on the right side
of the picture above) from which the oil is drained and a measured amount is
then added back in.
Now that we understand the differences between direct and clutch drives,
let's take a look at three other means for getting your gas scooter to move.
Scooter Belt Drives
Your gas scooter belt is very similar to the belts
used in your car to transmit motion from your engine to the various fans,
pumps and generators. In a gas powered scooter, the belt connects the
clutch described above, and to the wheel of the gas scooter. Belts
typically run much quieter than chain drives, but compared to the exhaust
noise of the engine, this difference would not be noticed. Belts can
have a tendency to slip when wet or when not adjusted properly.
However, some gas scooters now used a toothed belt which engages with a
toothed wheel on the clutch to prevent slippage. Also, unlike a chain,
a belt may require more disassembly of the gas scooter to replace it since
it cannot cut like a chain to take it on or off. Some scooters
use a combination of belts and chains. There might be a belt between
the engine mounted centrifugal clutch and the input to the gearbox, and then
a chain from the output of the gearbox down to the sprocket on the tire.
You can purchase belt grip sprays from a hardware store that will help an
older belt stop slipping. This should be regarded as a temporary fix
however and the should be replaced as soon as possible.
Scooter Friction Drives
Friction drives are the lowest technology
gas scooter drive
available. A gas scooter friction drive is nothing more than a hardened steel
shaft coming out of the gas scooter engine and scrubbing against the rubber
wheel of the gas powered scooter. This shaft is typically referred to
as a spindle pattern embossed on it to enhance the bite into
the tire. Friction drives are direct drives,
and therefore require the engine to stop every time the scooter stops.
Friction drives positively do not work in the rain, and can result in your
drive tire wearing out if they slip. Friction drives typically require
a solid rubber tire to rub on since they do abrade and actually reduce the
tire diameter with time. Solid tires do not provide nearly the shock
absorbing capacity of an inflated tire. GoPed scooters are noted for
their high preponderance of friction drives but have an incredibly loyal
Gas Scooter Chain Drives
Chains require special chain lubricant. Usually this is an
aerosol foam type of a spray. You must allow at least 8 to 10 minutes
after spraying the foam on the chain for it to penetrate between the roller and
pins that make it up. If you ride the gas scooter to soon, the centrifugal
force will simply sling it off on to your seat or worse yet the back of your
Changing the size of the sprockets
on your scooter will have a direct impact on the speed and climbing ability of
your gas scooter. This is a fairly advanced upgrade as it would involve
lengthening the chain if moving up to a higher gear ratio (more power, less
speed). One advantage of a friction drive is that you can vary the gear
ratio very easily by simply changing to a different diameter spindle (the part
that rubs on the tire).
try to answer all your questions in the
articles above. Still have a question? Write to us at firstname.lastname@example.org
and we'll answer it.
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