Check the Scooter for Worn-out Belt and Weight Roller If Not Accelerating and Not Reaching Top Speed!

01-2b.jpg How to

A scooter accelerates smoothly from start to maximum speed with just a twist of the throttle. The drivetrain is supported by the drive pulley, drivetrain pulley, and drive belt, the diameter of which varies infinitely depending on the engine speed. The drivetrain of moped scooters tends to be unmaintained, but if you notice any discomfort when riding, check it out.

If you feel a loss of power or the top speed, suspect drivetrain wear.

02-2b.jpg A delivery vehicle with baskets attached to the front and rear to carry a full load of newspapers. The Super Cub is often associated with newspaper delivery, but the scooter type is also popular among female deliverymen because it is easy to get on and off.

03-2.jpg It's surprising that a moped scooter can travel 80,000 km, but it's a tough distance for a scooter, not only for the rider but also for carrying heavy newspapers. Naturally, a scooter can't be ridden this far if it's left unattended, so of course engine oil changes and maintenance of the brakes and drive train are essential.

While a manual transmission allows the rider to select the number of gears at will, a scooter's continuously variable transmission allows the scooter to adjust the gear ratios on its own according to the engine speed and load. As a means of commuting to work or school, scooter owners who are not interested in the mechanics of the scooter but only see it as a convenient companion may take it for granted that the scooter will always perform when the throttle is twisted, but this continuously variable transmission is quite an excellent mechanism.

Since the late 1970s and early 1980s, when scooters replaced mopeds for commuting and neighborhood shopping, known as soft motorcycles, the scooter's drivetrain of two sets of pulleys and a V-section rubber belt has remained essentially unchanged.

The cylindrical weight rollers built into the drive pulley roll outward by centrifugal force due to the increase in engine speed, a very simple physical action that keeps the vehicle body and rider at 60km/h. A moped scooter carries you to the world of h. The fact that the starting dash is faster than a transmission motorcycle that is sluggish in changing gears is also true for AT and MT in automobiles.

As a side note, the AT in automobiles automatically shifts gears through the transmission gears that are divided into multiple steps, but the CVT uses a metal belt to connect the two sets of pulleys, just like the drive system of a scooter, and shifts gears steplessly. However, the CVT differs from moped scooters in that the pulleys are controlled electronically, rather than being left to the weight rollers. This is also used in motorcycles, and the Honda Forza Z of the mid-2000s was equipped with a mechanism that electrically controlled the drive pulley.

Returning to the moped scooter, let's look at the drive pulley, which is directly connected to the crankshaft among the two sets of pulleys. The drive pulley has a structure that looks like two umbrellas facing each other, and a rubber belt with a V-shaped cross section is sandwiched between them. The distance between these two umbrellas changes automatically according to the engine speed, and the diameter of the belt between them also changes automatically.

The movement of changing the diameter of the rotating belt is easy to understand if you imagine a bicycle gearbox. In a bicycle with gears on both the pedal side and the rear tire side, the gear on the pedal side is smaller and the gear on the tire side is larger to reduce the force on the pedal when starting. And to ride at the highest speed, the pedal side gear should be larger and the tire side gear should be smaller.

The same thing happens in the drive system of a scooter. When the engine is stopped and idling, the drive pulley is near the center of the drive pulley. Then, as engine speed increases, the weight rollers in the two facing umbrellas, called the movable drive faces, move outward by centrifugal force, narrowing the distance between the two umbrellas and moving the drive belt between them outward from the center.

This movement moves the belt from near the outer diameter of the pulley on the rear tire side to near the center, and the trick is that the rear tire rotates faster, increasing the speed.

POINT
  • Point 1: The scooter's drive system, which combines front and rear pulleys and a drive belt, has been inherited since the 1980s.
  • Point 2: Stepless gear shifting is achieved by the drive belt rotating while sliding on the pulley surface, but there is also wear due to friction.

Roller and belt maintenance is inevitable for scooters.

04-2.jpg To remove the movable drive face, put a non-turning holder over the fin of the drive pulley face and loosen the center nut. The term "movable drive face" or "drive pulley face" is the Honda way, while Yamaha uses the term "primary sliding sheave" or "primary fixed sheave".

05-1.jpg The weight roller is stepped and worn beautifully. The weight roller is sandwiched between the movable drive face and a metal plate called the ramp plate, and as it is repeatedly moved outward and backward by the centrifugal force of engine rotation, the parts that are hardest hit are worn.

06-2.jpg The groove in the movable drive face where the roller rolls will also be gouged as shown. When the engine is stopped and idling, the rollers are near the center and gradually move outward as the rotation increases. As the rollers and grooves wear, the movable drive face moves less and less, and the pulley face becomes less and less wide. This means that the drive belt cannot travel to the outer edge of the pulley face and the maximum speed is reduced. The cause and symptoms are clearly linked.

07-2.jpg Normally, the angle should be constant from the center to the outer edge, but the pulley surface is wavy due to friction with the drive belt. If the drive belt cannot move smoothly even if the pulley moves, it can lead to poor acceleration and a lack of power. The symptoms vary depending on the state of wear, but nothing good will come from continuing to ride like this.

The weight rollers in the drive pulleys, which move by centrifugal force in conjunction with the increase or decrease in engine speed, are constantly subjected to friction and consequently wear gradually. The drive belt, which is sandwiched between the pulleys, also wears down in the action of changing its diameter by moving while being rubbed between the two umbrellas.

Typical symptoms caused by wear of the rollers and belt are lack of power when starting and reduced maximum speed. The wear of the rollers is shown in the reference image, where part of the circle has become flat due to wear. Normally the rollers should move smoothly through the roller grooves in the movable drive face, but as they become stepped, the movement is not consistent and the pulleys may be slow to narrow even though the engine speed is increasing. This is the same as selecting a higher gear when you are not going fast enough, and can cause you to feel underpowered.

Also, as the belt wears and becomes narrower, the belt will not be able to spread all the way to the outer edge of the pulley even though the two umbrellas on the drive pulley are narrower, resulting in a lower top speed. Furthermore, if the shoes of the centrifugal clutch built into the drive pulley are worn out, although I will not mention it this time, it will slip at the clutch meet when starting and the start of driving will be poor.

Parts such as pulleys and belts cannot be oiled or greased, so there is no way to reduce the wear and tear caused by friction and wear. Just like tires and brake pads, the more you ride, the more they wear out. In other words, your scooter's drivetrain is not maintenance-free.

However, when weighing up the distance between the need for maintenance and the life expectancy of a typical scooter, if the life expectancy comes first, wear and tear in the drive train will not be noticed as a fault. Also, wear and tear may not be recognized as a defect if the owner does not notice a decrease in gearshift timing or top speed. As a general rule, the legal speed limit for a 50cc moped scooter is 30km/h. So you can also think that you don't have to shift to the highest speed.

POINT
  • Point 1: Weight roller and drive belt wear is inevitable for scooters.
  • Point 2: The distance that maintenance will be required and the distance until the vehicle is replaced or scrapped will determine whether or not the drivetrain will be maintained.

Scooter maintenance is also interesting because it makes sense when you compare wear and symptoms.

08-2.jpg Replace worn movable drive face and weight roller with new ones. The drive belt is assembled without grease because oil on the belt will directly lead to slippage. Therefore, it will eventually wear out, but this part is consumable for a scooter with many miles on it.

09-2.jpg The drive belt has a V-shaped cross-section to match the angle of the pulleys. The inside of the belt is convex and concave to allow it to follow a small turning radius. It is important to check that the width of the belt has not reached the limit of use due to wear and that there are no cracks at the bottom of the concave surface.

10-1.jpg Since the width of the drive belt varies from model to model, check the compatible model when using a belt other than the genuine part for replacement. Also, when tightening the center nut on the drive pulley face, if the belt is still caught in the pulley face, it may cause the nut to loosen, so it is best to widen the rear tire side drive pulley and push the belt close to the center and tighten the nut while it is touching the outside of the drive pulley.

However, it's not a good idea to keep riding with a worn-out drivetrain. What I'm going to introduce here is a 4-stroke model Yamaha Ghia used for delivering newspapers, with a mileage that is about to reach 80,000 km. 80,000 km is quite a distance for a moped scooter, but it's also quite serious for the drivetrain when it's loaded with heavy newspapers and used repeatedly to start and stop.

We have done maintenance on the drive pulley in the past, but when we removed it this time, we found that the weight roller was still unevenly worn. In addition to the wear of the weight roller, there was also an abnormality in the movable drive face. Specifically, the grooves where the weight rollers roll are worn out and the face where the belt moves is wavy. It is common to replace only the rollers while reusing the movable drive face. However, the more miles you travel, the worse the roller grooves become, so be careful with scooters used for business.

The wavy surface on the front side of the movable drive face, where the drive belt contacts the pulley surface, is typical of the wear of a newspaper delivery vehicle that is repeatedly go-stopped at low speeds without being used to its maximum speed. If the vehicle is loaded with heavy newspapers and continues to perform under a heavy load, the engine speed may increase but the vehicle will not be able to switch to a higher gear. This is like a transmission motorcycle that keeps riding in low gear or second gear.

By using the low-speed side with high torque, the drive belt wears and becomes narrower. The narrower the width, the less the belt can travel to the outer edge of the drive pulley and the lower the maximum speed. If you look at the removable drive face, you will see that the wear marks on the belt do not reach the outer edge. It is unlikely that you would be riding at top speed delivering newspapers, but there is a nice connection between belt width wear and reduced top speed.

Some people think that scooters are just a means of transportation and should not be tinkered with, but there is a cause for wear and tear, and removing the cause is a sure way to restore the motorcycle. The process is the same for both scooters and motorcycles, and you will feel a sense of accomplishment when the problem is solved.

POINT
  • Point 1: Worn-out is sure to progress in the drive system of a moped scooter that has been driven a long distance under a high load.
  • Point 2: Replacing the movable drive face, weight roller and drive belt is an essential part of drivetrain maintenance for scooters with high mileage.
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