Scooters are easy to ride to work, school, and shopping, and when they are in the 125-150cc class, they are fast enough. Compared to motorcycles with transmissions, scooters are often thought of as maintenance-free, but of course, the tires and brakes will wear out. In addition, the V-belt and weight roller, which are the key to stageless shifting, can't be left to rot. Do basic maintenance on your drivetrain before it becomes unfit to ride.
Both the latest models and 1980s moped scooters have the same basic shifting principles
When the belt case is removed, the front and rear pulleys and the V-belt can be seen. The outside of the belt case has a plastic cover to muffle sound and protect the case, and some models have ducts inside the belt case to ventilate the outside air.
In the 1980s, scooters were mainly two-stroke mopeds that were built to be crushed like a motorized bicycle. Scooter racing was also popular at the time, and there was a culture of modifying cheaply purchased vehicles to play with them.
However, if you look at the current scooter category, you can see that the 50cc models have become a 4-stroke machine with injection, and although I'm not sure about the tuning, I can no longer say that I've removed the exhaust port. Also, the 50cc moped class itself has shrunk, and the power of mopeds (Class 2 to 250cc) and small motorcycles (Class 1 to 250cc) has increased.
Unlike the old days, modern scooters have complex cowls and a sense of luxury, a full range of functions around the instrument panel, and a large trunk capacity under the seat, making them very practical.
It's such an attractive scooter, but if you strip away the exterior and focus on the drive part, the mechanism itself is almost unchanged from the 1980s scooters. Even gear transmission vehicles have a clutch, a transmission, and a drive chain to drive the rear tires, a mechanism that has been the same since the 1950s. However, the drivetrain of scooters up to the light two-wheel class is the same as the DIO and JOG of the two-stroke era, and even with the addition of a few electronic controls in the 250cc and higher classes, the principle of stageless shifting is not too different.
The pulleys on the tire side are connected to the engine side by a rubber V-belt, and the diameter of the pulleys on the tire side changes in conjunction with the infinitely variable diameter of the engine side pulleys in response to changes in engine rotation. When the pulley diameter is large, the tire side is small, and when the engine side diameter is small, the pulley diameter on the tire side is large.
The change in pulley diameter is easy to understand if you replace it with gears on a bicycle with a transmission, just like when you're in a larger gear, the pedals are lighter but slower, and when you shift into a smaller gear, the pedals are heavier, but the speed increases.
- Point 1: Stageless shifting of the scooter is done by changing the diameter ratio of the front and rear pulleys.
- Point 2: Shifting gears with the belt has been a constant mechanism since the 1980s
V-belt wear is noteworthy due to the increased durability of the motorcycle
The drive pulley on the engine side has a drive pulley face (right) and a movable drive face (left) facing each other, and the V-belt moves within the width of the pulley determined by the two faces to change the gear ratio infinitely. The width of the drive pulleys is wider at low engine speeds and narrower at high engine speeds. When the pulley width becomes narrower, the V-belt is pushed outward and the speed increases.
The V-belt is constantly being pulled and bent, so deterioration can cause it to crack on the inside. If cracks are identified, replace them, even if the wear is less than the limit.
The usage limit of the V-belt varies from model to model, so check the service manual.
It would be clearer to manage it by mileage, even if the wear limit is not reached.
Even with the introduction of outside air into the belt case, belt wear particles accumulate in the case. Use a parts cleaner to clean it when you replace it.
As long as the front and rear pulleys are connected by a rubber belt, friction is inevitable as they rotate. This is even more so, as the rotating diameter is forced to change while being held between the front and rear pulleys. Because of this mechanism, the V-belt wears down and becomes narrower and narrower. The position of the belt between the pulleys will gradually change. If the belt continues to run in this state, the belt may be cut off due to a lack of strength if it becomes narrower as wear progresses.
In the heyday of the 2-stroke scooters, there was a problem with the V-belt being subjected to the sudden cutting of the unweathered belt due to the driving force being applied to the V-belt by the high-revolution tuning. While such cases are rare on modern 4-stroke scooters (with the exception of some high-tuned 4-stroke scooters), the increased durability of the engine and chassis has led to increased mileage per vehicle, which has caused stress on the V-belt.
V-belt replacement is judged by the actual measured belt width, but the mileage is also based on the mileage. It may vary from manufacturer to manufacturer, but for example, for Yamaha vehicles, the V-belt on a 50cc to 250cc scooter is specified to be replaced every 20,000km. On a severe-condition bike, the figure is 10,000km, and while there may not be many users who drive a 50cc JOG for 20,000km, 20,000km may not be uncommon on a 250cc XMAX.
Even gear transmission vehicles change the drive chain and sprockets based on mileage, so it's only natural to think about changing the drive belt on a scooter, but due to the nature of the scooter ride, you might be tempted to think of the drivetrain as maintenance-free! But even with stageless shifting, as long as there are wear and tear parts, that's where maintenance is needed.
To replace the V-belt, remove the belt case and remove the drive pulley on the engine side and the drive pulley on the tire side. You will need a wrench to remove the holders that hold each pulley in place and the bolts that hold the center of the pulleys in place.
On scooters with high mileage, the inside of the V-belt case is often contaminated with worn belt dust, so after removing the belt, clean it thoroughly with parts cleaner before installing a new belt.
- Point 1: Change the V-belt periodically according to the mileage.
- Point 2: Think of the V-belt as a consumable item, just like the chain.
It's also important to check the weighted rollers that rotate while rubbing
The weighted rollers on the backside of the movable drive face allow you to change the timing of the shifting by changing the weight. Standard weight is fine for normal city driving, and it's important to check for diameter changes and uneven wear.
The drive pulley on the tire side is subject to a narrowing force caused by the tension of the internal spring. When assembling a new belt, the drive pulley can be assembled smoothly by compressing the spring to widen the pulley and pushing the belt to the parking area.
Along with the wear on the V-belt, one thing to check is the wear on the weight rollers in the drive pulley. The weight rollers are cylindrical in shape and there are several of them on the back of the drive pulley (sometimes called the moveable drive face).
The drive pulley is connected to the crankshaft of the engine, and as the engine speed increases, the rotation of the pulley also increases, and centrifugal force moves the weight roller to the outside of the pulley. This causes the inner width of the drive pulley to narrow and the V-belt in the center of the drive pulley to be pushed outward.
This movement changes the reduction ratio, and the V-belt widens the width of the drive pulley on the tire side to increase the speed. Therefore, the function of the weight roller is very important for the smooth movement of the drive pulley.
And just like the V-belt, these weighted rollers also wear out as the mileage increases. During the constant going up and down the slopes inside the pulleys as the engine rotates up and down, the cylindrical rollers can become smaller in diameter due to wear, and in some cases, may even become less than perfectly circular due to uneven wear.
This may cause the drive pulley to become narrower and the acceleration and deceleration may be uneven even though the engine rotation is up. Unlike the V-belt, there is no indication of when to replace the weight roller by mileage, but the dimensions of the cylindrical portion of the weight roller specify that it should be replaced when it has worn down to less than the limit, so you should also check the condition of the weight roller on the backside after removing the drive pulley.
Unlike chains and sprockets, the drivetrain of a scooter is not visible from the outside, so it's difficult to determine the wear and when it's time to replace it, so it's important to maintain it according to the mileage.
- Point 1: Weight roller wear inhibits the smooth shifting
- Point 2: Determine when to replace rollers by wear and tear.