A belt drive is a system of drive and driven pulleys connected by a drive belt. It has been known since ancient times and was used in the first mills, in which horses acted as engines, and the belt consisted of pieces of rawhide sewn together into a ring. With the advent of internal combustion engines, transmission began to evolve rapidly.
Belt drive of the rear wheel of a motorcycle began to be used as soon as the design of a two-wheeled vehicle appeared, but over time the belt lost its leading position. It got wet, stretched, and most importantly, did not allow an increase in torque, and therefore the power of the motorcycle. For some time, the belt completely disappeared from the design of the unit, but today a motorcycle with a belt drive is easy to find on the street. The fact is that modern technologies have made it possible to produce belts from artificial fibers, high-quality rubber and durable Kevlar threads.
Toothed belt
It transmits rotation not only due to friction, but also due to the engagement of the teeth with the geometry of the pulley wheel. This achieves high transmission rigidity, synchronization of shaft rotation, high transmission efficiency and reduced load on the bearings of both the drive and driven shafts. The use of a timing belt allows greater power to be transmitted at significant speeds, but the design requires complex and precise adjustment. This is due to the fact that its service life depends on the degree of tension of the belt, and since it is expensive, frequent replacements will lead to significant expenses.
Eliminating the causes of the malfunction
If after performing the manipulations the scooter starts, that’s good, but you shouldn’t relax. Be sure to check for possible faults. What to do to prevent this situation from happening again:
- Clean or replace the air filter. You can make sure that this is the reason by simply trying to start the engine with the filter installed and without it.
The air filter can be covered with a foam cover - Refuel only with high-quality fuel at trusted gas stations. After refueling at some stations, I had to clean the carburetor jets every time.
- Check the condition of the spark plug. Pay attention to the gaps between the electrodes, the amount of carbon deposits and check the spark. The spark is checked as follows: a candle holder is put on the unscrewed spark plug, the thread is leaned against the cylinder and the engine is turned by the starter. In this case, the candle should give a powerful spark. If the spark is weak, adjust the gap; adjusting the gap does not help, change the spark plug. If the new spark plug produces a weak spark, then you need to pay attention to the ignition coil.
To check for a spark, place the spark plug against a metal housing and turn the starter
After checking the spark, check the gap between the electrodes
To check the gap between the electrodes, use special patterns
Advice! If the condition of your engine is far from new, then cleaning or even replacing the spark plug should be done more often.
- Adjust the quality of the mixture. Set the carburetor mixture quality screw to the optimal position (where the quality screw is located, see this article), clean the carburetor on the moped. If you have a scooter with an injector, monitor the condition of the injectors. Use an injector or carburetor cleaner.
- If you have a 4-stroke engine, pay attention to the valve adjustment. Incorrect release timing can also cause dirty spark plugs.
- The battery should always be well charged and the starter in good working order. After all, candles are often filled in in winter, and in cold weather a reliable battery is required.
- The quality of oil in the frosty season also affects the success of starting a scooter. The oil must be fresh and of the required viscosity for your local temperature.
Advice from experienced motorcyclists! If a spark plug is flooded, you should load the engine at high speeds at least once a week. This ensures that the cylinder and spark plug are purged from accumulated carbon deposits.
Advantages and disadvantages of belt drives on motorcycles
The advantages of belt drive include:
- Unpretentiousness. The belt does not require special care; it is enough to periodically visually check for cracks and tears.
- Compliance. Elastic rubber smoothes out all sudden changes in power, absorbs shock loads and thus ensures a smooth ride.
- High efficiency. Losses when transmitting rotational motion from the engine to the wheel are minimal.
- The belt drive does not create noise, which ensures a comfortable ride.
- Durability. On average, a belt drive is designed for a mileage of 50 thousand kilometers.
However, with all the advantages, belt drive also has a number of disadvantages. You can start with the fact that the width of the belt does not allow it to be installed on sports motorcycles with a power of 110 kW or more. Protective covers around the transmission are mandatory, since if a foreign body gets into the belt, it will inevitably break. And motorcycles with covers are designed to be ridden only on asphalt.
Motorcycles generally use timing belts, and the rear pulley is made of aluminum coated with durable chrome. The chrome gradually wears away and, in the end, bare aluminum remains. As a result, the belt teeth begin to grind down, which leads to belt rupture. Therefore, along with the belt, the pulley also has to be changed. We should not forget about possible manufacturing defects, from which no production is insured. Both it and incorrect installation of the belt will lead to its rupture. The belt must always be at a certain tension - sagging will accelerate breakage. You can check the tension in any motorcycle workshop using a special device. Typically, sagging is allowed within two centimeters, but this figure is not a standard, it all depends on the individual characteristics of a particular model.
Hi all. We would like to share our project - installing a belt drive on a Honda CB400 instead of a chain drive.
The project began in the fall of 2021. It all started with the obvious - measurements on a motorcycle. The question was whether we could physically implement the belt without any “collective farm”. The main problem turned out to be the drive pulley. Our choice fell on a belt with a 14mm pitch (this pitch is used on Harleys). Having measured the space near the crankcase in the area of the drive sprocket, we realized that a pulley with 20 teeth, no more, would suit us. In the process of studying the catalogs of pulley manufacturers, it turned out that the minimum number of teeth for a 14mm pitch is 28 teeth, which naturally does not suit us. It was decided to draw a more than non-standard drive pulley from scratch with dimensions of 20 teeth and a pitch of 14mm. With the driven one, everything is simpler - a pulley with standard parameters of 56 teeth is built automatically in a special program. The gear ratio turned out to be 2.8 versus the standard 2.93. In the spring of 2021, the first version was already installed: both pulleys are made of aluminum (B95 alloy) on an erosion machine, a contitech industrial belt with a pitch of 14 mm. As a result, it turned out to completely replace the chain with a belt without making any changes to the design of the motorcycle.
About 3000 km were covered on this version. During this time, the driving aluminum pulley wore out very intensively, its teeth became very thin, which caused the belt to wear out and fail - the sharpened edges of the pulley teeth literally gnawed and pulled out the belt teeth. About 6 teeth peeled off, but the motorcycle made it home on its own, but the driven pulley was practically free of wear. After analyzing the first version, it became clear that the following needs to be done: the drive pulley is made of steel and strengthened, and the driven aluminum pulley is cold anodized. All this was already clear by the middle of the 2021 season, then there were delays in manufacturing... As a result, we installed the second version in the fall of 2019: as planned, the drive pulley was made of steel and hardened to 45HRC, the driven pulley was treated with cold anodizing, and a new one was installed the belt, as in the first version, is contitech.
At the moment, about 2000 km have been covered on this version.
Now all that remains is to run the mileage on this version to find out its service life.
There are also plans to protect the lower branch of the belt in the area of the driven pulley.
short video after installing the latest version
Alternative transmission options on motorcycles
A chain is the simplest, most reliable and common way to transmit torque to the rear wheel. The main disadvantage of chain transmission is that it requires constant maintenance. The chain has to be lubricated quite often, and the centrifugal force sprays the lubricant throughout the motorcycle from the gear side. Another disadvantage is the fragility of the chain - the operational period is no more than 20 thousand kilometers. But the chain confidently transmits high engine power, has small dimensions and easily passes dirt between the links - slush does not interfere with the operation of the transmission at all.
The cardan, unlike the chain, does not require careful maintenance, and since it is damaged extremely rarely, servicing is not difficult. Most often, such a transmission can be seen on touring motorcycles and on those intended for long trips. The disadvantage of the cardan is its heavy weight. This is the heaviest drive option and is therefore never used on sports motorcycles. The second significant drawback is the need for a driven bevel gear on the rear axle, which significantly increases the unsprung weight.
Belt drive on suzukiSV650
The pulleys could also be ordered here. According to the mind, the body is made of aluminum and the ring gear is pressed on. And when it is erased, the old crown is cut off and a new one is pressed on.
If stones do not get under the belt, the pulleys will never wear out. Manufactured from aluminum alloys by injection molding (motorcycle). And the tooth strength of the aluminum pulley is enough for the entire service life. The belt is a consumable item. A common option is a belt made of heat-resistant rubber reinforced with aramid fiber. The ideal option is a polyurethane belt reinforced with Kevlar.
And Harley (and not only) driven pulleys are made of aluminum, driving ones are made of cast iron.
what would be the consequences of using a belt with a smaller pitch? will it reduce the service life? Or will it just not withstand the load?
It is necessary to look at the permissible load characteristics of this belt (the dealer should provide it). What torque at a specific number of revolutions is it designed for? And at what maximum speed? A belt with a smaller pitch allows the installation of a smaller drive pulley (this probably influenced your choice) and higher speeds compared to large-pitch ones (when transmitting, accordingly, less torque).
The manual for your motorcycle contains data on the maximum engine torque at a given speed and gear ratios. Torque and power data is taken from the crankshaft (only Ducati claims power and torque at the rear wheel). So take these numbers as a basis. Ignore transmission losses. Take into account two options (first gear (maximum power and torque at minimum speed) and top gear (maximum power and torque at maximum speed of the transmission output shaft)).
If your calculations confirm the choice of belt and you are confident in the correctness of the choice, the only thing I can advise is to cut out the core from the driven pulley (leave 10...12 mm of the crown thickness from the bottom of the tooth cavity to the edge of the hole) and press it onto the duralumin disk. But here you have to be very careful. The pulley is made of cast iron; if you simply press it onto a duralumin pancake using a press, the crown may burst. It’s better to make the shaft/hole pair in scratches, put it on a super-strong clamp, and to make it even more important, you can fix the connection joint with screws (the screws are also on the clamp).
This way you will radically reduce the unsprung mass and your set will not be lost.
Modified on February 19, 2011 by user Rom-Romych
