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Gas Scooter Clutches, Transmissions, Chains, and Friction Drives

The 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 Scooters 

  • 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) gas scooter centrifugal clutch  frontand back.gif (173x288 -- 16453 bytes)which is the most common clutch used for gas powered scooters. 

Centrifugal Clutch Gas 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 - When the engine is turning, so is the shaft.

  • A pair of cylindrical clutch weights gas scooter clutch shoes .gif (132x132 -- 3644 bytes) attached to the center shaft (shown installed to the right, and loose to the left), along 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 gas scooter transmission .gif (132x132 -- 10744 bytes) 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.

Gas 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.

Gas 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 following.

Gas Scooter Chain Drivesgas scooter chain links .gif (139x167 -- 15354 bytes)  

  •  Chain drives are by far the most rugged of the three gas scooter drive choices.  Chain drives are similar to what you have on your bicycle namely, two sprocketsgas scooter sprockets .gif (132x132 -- 1069 bytes) connected together bygas scooter chain txchain.gif (119x41 -- 1065 bytes) a flexible metal chain.  Chain  drives will not slip, but do require that they be properly adjusted and are more sensitive to misalignment than a belt drive.  Both the tightness of the chain (how far apart the engine and the driven wheel are) and the alignment of the clutch and drive wheel sprockets are critical.  Chain drives usually have what is called a gas scooter chain master link master link (pictured to the right) in them to permit removal of the chain.  This is an advantage over belt drives that often require removal of the wheel or engine from the scooter to remove the drive belt.  If the chain does not have a master link (some come from the factory without it) then you will need a chain breaker.  The shown below costs about $15.00.  Better to try and borrow a friend's since this is a tool that you typically only use once for the life of the scooter!  without having to remove the engine housing of the gas scooter to access it.  Drive chains must be regularly lubricated with a good quality chain lube to keep them rust free and to reduce friction. gas scooter chain breaker 

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 pants.

Changing the size of the sprocketsgas scooter big sprocket.gif (177x150 -- 5579 bytes) 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).


  We try to answer all your questions in the articles above.  Still have a question?   Write to us at info@gas-scooters-on-the-web.com and we'll answer it. 




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