A clutch is one of those parts of a motorcycle used most of the time, although we rarely think about it. Theoretically, it is not much to say; it allows a rider to detach the power from the back wheel while the engine spins and the motorcycle remain still.
The clutch, for me personally, is a very interesting motorcycle part. That is because of how perfectly it is designed, and its working principle is fascinating to me. That is why this article will tell you all the necessary and interesting things like clutch working principle and so on.
So how does a motorcycle clutch work? A clutch engages and disengages the motorcycle transmission by squeezing the friction plates together. Once the clutch lever is pulled, the power from the engine doesn’t go to the transmission, allowing you to shift gears; when you leave the clutch lever, the power is sent to the transmission again.
Continue reading as we will cover other clutch-related topics further in this article.
Table of Contents
How Does a Motorcycle Clutch Work?
The rider needs to release the clutch lever if he wants the power to transfer to the rear wheel; this also lets springs press the plate against another plate linked to the back wheel through the chain and gearbox. So the theory behind this is that the engine power spins a disc that looks like a big washer with a big opening in the center.
Extra power is shifted to the back wheel, just as the friction between two plates expands, as far as the plates are sealed, and max power shifts from the engine to the wheel.
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Since motorcycles have narrow space in the frame of 4-cylinder engines, it can get complicated. If you had only two clutch plates, they would need to be huge to have sufficient surface area to produce enough friction to shift the power. Because of this reason, most motorcycles got multi-plate clutches.
The theory behind this is similar; just as an alternative of having two big plates, there may be more than 10 smaller ones. One-half of the plates will be linked to the crankshaft (right on the end of the crank or inverted by a primary drive gear), and the other half will be connected to the gearbox input shaft.
The friction material is connected to the faces of the crankshaft plates, which use tabs on their rims for locking into the clutch housing. The gearbox plate is made out of plain steel with teeth on its internal extent engraved into the gearbox shaft.
Note: Both types of plates are alternated; this means that both parts of all (apart from the end ones) get used to generate friction. After releasing the clutch lever, the clutch springs get released and pressed on a pressure plate that connects the clutch plates equally.
Clutch History
Back in the days and the beginnings of motorcycling, some bikes didn’t care about clutches; that being said, every start was a sudden start, and stopping involved taking your weight off the seat and allowing the back wheel to spin slowly. Also, you couldn’t get them without a clutch since there were no gears.
Today, most bikes have a manual clutch built-in (not in an automatic gearbox). They have multi-plate, which means multiple friction surfaces are utilized and run in oil (wet).
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How Many Clutch Plates?
The number depends on the size of plates (smaller plates mean more plates), how much power needs to be transferred (in case of transferring more power, more plates will be needed), what kind of friction material is used (if more slippy more plates are required), and the power of the clutch springs (weaker springs means more plates). Huge power in a compact motorcycle means a heavy clutch.
Since friction is a very important segment, it may look a little bit odd for most clutches to run in a lubricate (engine oil).
Note: Oil’s purpose is to save your clutch from burning out. Friction produces heat which could simply destroy the frictional material.
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Wet Clutch VS Dry Clutch
Wet Clutch
Wet clutches are very durable, can last for ages, and take a lot of abuse. This means that the moving parts such as the bearings, the bushes, and the plates have smooth movement. Although even specially-created mixtures of friction material aren’t highly effective in oil, this requires more plates, leading to more weight.
Dry Clutch
Dry clutches lose a smaller amount of power while their plates produce more friction in comparison with wet clutches. This enables them to be lighter and smaller than wet ones. Therefore they have been used by Ducatis for decades and in MotoGP bikes.
One of their characteristics is producing an engine-about-to-explode clank ( the sound comes out of plates jingling and vanishes as soon as you let the clutch out). Dry clutch is often used by Motto Guzzis and BMW twins, and the reason for that is because the crank works out of the front to back; this means there is more space for a big car-style dry clutch.
Note: Dry clutches, in general, are not used so much on road bikes since they produce more noise and are not so durable, especially when they get hot.
Motorcycle Clutch Characteristics
Modern motorcycle engines are built of gearbox and clutch in one segment, along with clutch and crankshaft combined. It wasn’t always like that. Engines and gearboxes were apart in British motorcycles connected with bolting to engine plates.
The clutch placed on the gearbox was guided by a primary chain out of a sprocket on the engine’s crankshaft while a chaincase protects and surrounds the chain.
In a classical motorcycle clutch, the engine runs the clutch outer hub. The clutch external hub could be a cylindrical drum approximately 6 inches in diameter. Its rim is around 1-1/2 inches tall. It bears inner facing ribs or splines that engage similar tabs on the outer diameters of some circular discs combined with friction material called the friction plates.
A separate inner hub is placed in the outer hub, connected to the gearbox’s input shaft. It is also cylindrical, and its outside surface has an axial spline. Other clutch discs are simply known as “steels,” engaging these splines intertwined with the friction discs. Both friction and steel discs change alternately in the “stack,” the frictions attached to the clutch outside drum, the steels connected to the inside drum.
On the top of the clutch plates is a spring-backed pressure plate that puts all the discs in a pile into frictional contact with each other. When a rider presses on the clutch lever, a mechanism lifts the pressure plate to its spring pressure and disconnects steel plates and the friction.
Once the engine is started and you want to move, you must first press the clutch lever; then, you need to place the transmission into the first gear.
The spinning engine rotates the external clutch drum and the five or more friction discs. The internal clutch drum and the steel plates connected remain static because shifting gears connect the gearbox’s input and output shafts.
Since the bike is static at this moment, the rear wheel, the drive chain, and both gearbox shafts are not in motion.
In order to move with your motorcycle, you need to turn your throttle slowly while at the same time letting the clutch carefully until you feel the “engagement point” ( the position of the lever where friction starts to happen between the friction discs and the steel discs).
Increasing friction makes the steel discs start to spin, first with low speed, which then starts to increase. They rotate the internal hub by turning the gearbox input shaft and the back wheel, whose massive torque- from 10-to 15-to-one general first-gear decrease between the rear wheel and engine speeds up your motorcycle.
When starting, the “slip phase” is where clutch friction makes the steel discs progressively catch up with friction discs and the external drum. After slippage ends, driving becomes stable and solid. Bikes clutches have functioned in this principle for a century with some modifications.
This video will help you Understand Motorcycle Clutch Working Principle:
Slipper-Assist Clutches
Slipper Clutches
Slipper clutches were first made for engine braking in road racing. When a rider presses a brake and releases the throttle, the rear wheel over the chain, clutch, gearbox, and primary drive, has to rotate the engine versus its inner friction.
CAUTION: If the bike leans into a corner while still braking, the friction torque could surpass the grip of the rear tire, and the bike might slide out of the road.
Reverse Torque
The reverse torque is used by a slipper clutch that functions through spiral ramps placed in the internal clutch drum to lower the spring pressure. As the bike’s momentum pushes versus engine braking, the clutch gets “unscrewed” by force, making the pressure plate raise.
By doing so, the motorcycle becomes more stable since this lets clutch slippage replace tire slippage. Spiral ramps can decrease clutch grip when the rear wheel moves the engine and expand clutch grip when the engine spins the rear wheel. A lever pressure can be reduced by 40 to 50 percent with this “assist” feature producing added pressure on the clutch stack.
These types of slipper-assist clutches can be found on many new motorcycle models.
Conclusion
The motorcycle clutch system is fascinating to me personally and to many of my fellow rider friends. It is fascinating how this gear transmission happens so fast and how the clutch is a perfect part which if it didn’t exist, none of this would be possible.