Motorcycle Transmission Secrets: Structural Essence and Maintenance Tips

I. The Mysterious Structure of Motorcycle Transmission System

(I) Chain Transmission

1. Chain Structure
   • Motorcycle chains are usually composed of inner link plates, outer link plates, pins, and rollers. Inner and outer link plates are generally made of high-quality alloy steel and undergo heat treatment to improve strength and wear resistance. Pins connect the inner and outer link plates, and rollers roll between the inner and outer link plates to reduce friction. Common specifications for chain pitches are 420, 428, 520, etc. The numbers indicate the length of each chain link (in units of 1/8 inch). For example, the pitch of a 420 chain is about 12.7mm. The width of the chain is determined according to the power and torque requirements of the motorcycle, generally between 6mm and 10mm. The diameter of the rollers is usually between 5mm and 8mm, and their surfaces are smoothly treated to reduce rolling resistance.
2. Working Principle
   • Chains transmit power by meshing with the front and rear sprockets. The front sprocket is driven by the engine output shaft, and the rear sprocket is connected to the rear wheel. When the engine is running, the front sprocket rotates and drives the rear sprocket through the chain, thereby driving the rear wheel to rotate. The number of teeth ratio of the sprockets determines the transmission ratio, and different transmission ratios affect the acceleration performance and maximum speed of the motorcycle. Generally speaking, the small sprocket has fewer teeth (such as 13 – 15 teeth), and the large sprocket has more teeth (such as 35 – 45 teeth). When driving at high speed, a smaller transmission ratio (number of teeth of front sprocket / number of teeth of rear sprocket) can reduce engine speed and improve fuel economy; when climbing or in need of large torque, a larger transmission ratio is more advantageous.

(II) Belt Transmission

1. Belt Material and Structure
   • Belts commonly used in belt transmission are generally made of rubber and high-strength fiber materials. Rubber provides flexibility and friction, and fiber materials enhance the strength of the belt. The internal structure of the belt usually includes a tensile layer, a buffer layer, and a friction layer. The tensile layer is generally composed of polyester or aramid fibers and can withstand a large tensile force. Its strength can reach several hundred or even thousands of Newtons. The buffer layer can absorb shocks and reduce noise, and its thickness is between 2mm and 4mm. The surface of the friction layer has special patterns and coatings to increase the friction with the pulley. The depth of the pattern is generally between 0.5mm and 1mm.
2. Working Method
   • Belt transmission relies on the friction between the belt and the pulley to transmit power. Pulleys generally have driving pulleys and driven pulleys. The driving pulley is driven by the engine. The belt is attached to the pulley by friction and drives the driven pulley as the driving pulley rotates, thereby driving the wheel. The groove shape and diameter of the pulley affect the transmission efficiency and torque transmission. Common pulley groove shapes include V-shaped and multi-wedge belt groove shapes. The angle of the V-shaped groove is generally between 30° and 40°, and the multi-wedge belt groove shape can transmit greater power in a smaller space. The diameter ratio of the pulley will also affect the transmission ratio. Generally, the driving pulley has a smaller diameter (such as 50mm – 100mm), and the driven pulley has a larger diameter (such as 150mm – 300mm).

(III) Shaft Transmission

1. Shaft Transmission Components
   • The shaft transmission system mainly consists of a transmission shaft, universal joints, gear components, etc. The transmission shaft is generally made of high-strength alloy steel and has high torsional strength. Universal joints are used to connect different angles of the transmission shaft parts to enable smooth power transmission. They are usually composed of ball cage or cross shaft structures. Gear components include driving gears and driven gears. The meshing of gears changes torque and rotational speed. The driving gear is connected to the engine output shaft, and the driven gear is connected to the rear axle. The module and number of teeth of the gears determine the transmission ratio and torque output characteristics. For example, gears with a module of 2 – 4 are combined with different numbers of teeth according to the design requirements of the motorcycle.
2. Transmission Principle
   • The power of the engine is transmitted to the transmission shaft through the driving gear. The transmission shaft, through the flexible connection of the universal joint, transmits the power to the driven gear of the rear wheel, thereby driving the rear wheel to rotate. The advantages of the shaft transmission system are high transmission efficiency, strong reliability, and no need for frequent maintenance. It can effectively transmit the engine’s torque to the rear wheel and is suitable for some heavy motorcycles and models with high reliability requirements.

II. Working Principle of Motorcycle Transmission System

(I) Power Transmission Process

1. From Engine to Wheel
   • In chain transmission, the rotational movement of the engine output shaft drives the front sprocket to rotate. The chain moves with the rotation of the front sprocket. Due to the meshing relationship between the chain and the rear sprocket, power is transmitted to the rear sprocket. The rear sprocket then transmits power to the rear wheel to make the motorcycle move forward. In belt transmission, the engine drives the driving pulley to rotate. The belt adheres to the pulley by friction. As the driving pulley rotates, the belt drives the driven pulley to rotate and finally drives the wheel. In shaft transmission, the engine output shaft drives the driving gear. The driving gear drives the transmission shaft to rotate. The transmission shaft then transmits power to the rear wheel through the universal joint and gear components.
2. Influence of Transmission Ratio
   • Different transmission ratios are suitable for different driving scenarios. In the starting and accelerating stages, a larger transmission ratio can provide greater torque, enabling the motorcycle to obtain power quickly. For example, when starting and stopping frequently on urban roads, an appropriate transmission ratio can make the motorcycle start faster. At high speeds, a smaller transmission ratio can reduce engine speed, reduce engine wear and fuel consumption. Taking a motorcycle as an example, when the transmission ratio is adjusted from 3.0 to 2.5 (assumed), at the same vehicle speed, the engine speed can be reduced by about 20% – 30%, thereby improving fuel economy and reducing noise.

(II) Torque and Rotational Speed Conversion

1. Torque Amplification and Rotational Speed Regulation
   • The transmission system realizes torque amplification and rotational speed regulation through different transmission methods and gear ratios. At low speeds, a larger transmission ratio can amplify the engine’s torque, enabling the motorcycle to overcome greater resistance, such as climbing or driving with heavy loads. At high speeds, a smaller transmission ratio can make the motorcycle obtain a higher speed, but the torque is relatively reduced. For example, when climbing, the motorcycle may shift to a lower gear, which is equivalent to increasing the transmission ratio to obtain greater torque to climb a steep slope.
2. Matching with Engine Performance
   • The transmission system needs to match the performance characteristics of the engine. High-performance engines usually require a more efficient transmission system to fully exert their power advantages. For engines that emphasize low-torque output, the design of the transmission system will focus on providing greater torque transmission at low speeds; for high-speed engines, the transmission system must be able to maintain stable power transmission at high speeds and achieve a smooth transition in different speed ranges.

III. Maintenance Secrets of Motorcycle Transmission System

(I) Chain Transmission Maintenance

1. Cleaning Frequency and Method
   • After every 500 – 1000 kilometers of riding, the chain should be cleaned. Use a special chain cleaner and spray it evenly on the chain. The amount of cleaner is generally 50ml – 100ml. Then use a brush or rag to gently wipe the chain to remove oil stains, dust, and impurities on the chain surface. Be careful not to use overly sharp tools to avoid damaging the chain. After cleaning, dry the chain with a clean cloth.
2. Lubrication Points
   • After cleaning, the chain needs to be lubricated. Choose a lubricating oil suitable for the chain. The viscosity of the lubricating oil is generally between 80W and 150W. Drop the lubricating oil on the joints between the rollers and pins of the chain. Each link should be dripped with about 0.1ml – 0.2ml of lubricating oil. Then rotate the rear wheel to evenly distribute the lubricating oil on the chain. At the same time, be careful to avoid dripping lubricating oil on the brake disc and tire.
3. Chain Tension Adjustment
   • Regularly check the tension of the chain. Generally, check it every 2000 kilometers or according to the vehicle’s usage. Use a chain tensioner or wrench to adjust the up and down swing amplitude of the chain. When the motorcycle is stationary, the up and down swing amplitude of the chain should be between 20mm and 30mm. A too-loose chain is easy to fall off or produce noise, and a too-tight chain will increase wear and power loss.

(II) Belt Transmission Maintenance

1. Appearance Inspection
   • After every 1000 kilometers or so of riding, check the appearance of the belt. Check whether there are cracks, wear, or aging phenomena on the belt. If there are slight cracks on the surface of the belt, it can continue to be observed and used, but the inspection period should be shortened; if the cracks are deep or there is serious wear, the belt should be replaced in time. The service life of the belt is generally between 20,000 and 50,000 kilometers, depending on factors such as belt quality, usage environment, and driving habits.
2. Cleaning and Protection
   • Use a clean damp cloth to gently wipe the surface of the belt to remove dust and stains. Avoid using chemical solvents or cleaners to avoid damaging the belt. At the same time, prevent the belt from contacting oil stains and sharp objects. When storing the motorcycle, try to avoid direct sunlight on the belt to extend the service life of the belt.

(III) Shaft Transmission Maintenance

1. Gear Oil Replacement
   • Generally, every 10,000 – 20,000 kilometers of driving, the gear oil of the shaft transmission system needs to be replaced. First, find the gear oil drain bolt and drain the old gear oil. The capacity of the gear oil varies depending on the model. Generally, it is between 100ml and 300ml. Then fill it with new gear oil. Choose gear oil suitable for the shaft transmission system. Its viscosity is generally between 75W and 90W. During the refueling process, be careful not to exceed the specified oil level line.
2. Universal Joint and Transmission Shaft Inspection
   • After every 5000 kilometers of riding, check whether the connection parts of the universal joint and transmission shaft are loose and whether the transmission shaft is deformed or worn. If the connection part is found to be loose, tighten the bolts in time. The torque of the bolts is generally between 30N·m and 50N·m. For slight wear of the transmission shaft, it can be repaired by sanding with sandpaper; if the wear is serious or deformed, the transmission shaft should be replaced in time.

By deeply understanding the structure and principle of the motorcycle transmission system and strictly following the maintenance methods, we can ensure that the motorcycle transmission system always maintains good performance, making the power transmission of the motorcycle smooth during driving and bringing us a safe and efficient riding experience. Whether it is passionate driving in pursuit of speed or daily commuting riding, a healthy transmission system is an indispensable and important part of a motorcycle. Let’s take good care of the motorcycle transmission system and start every wonderful riding journey.