The clutch engagement point determines how the engine couples to the gearbox sprocket and disengages the clutch plates. Having a badly adjusted engagement point can lead to unwanted power loss. There are multiple ways you can adjust the motorcycle clutch engagement point.
The 2 ways you can adjust motorcycle clutch engagement point are:
- Adjust the barrel adjuster
- Adjust the angle of the clutch arm
Adjusting the clutch engagement point is an essential part of maintaining your motorcycle, especially if you are experiencing a loss of power. In this article, we will go into detail on how to adjust the motorcycle clutch engagement point, and what type of motorcycle clutches there are.
What Is Clutch Engagement Point On A Motorcycle?
The clutch engagement point on a motorcycle is when power from the engine is completely coupled to the gearbox sprocket. Since the clutch controls the amount of coupling, it also determines how much power from the engine goes to the rear wheel. So, having the right engagement point is key.
If the clutch does not fully engage or couple to the gearbox sprocket, there is a loss of power in the transmission. This is very evident in low engine capacity motorcycles of 49 cc where every bit of power is needed to move the load. Engine capacities of 100 cc and above are not as critical as they can generate enough power to carry the rider and a pillion passenger.
The efficiency of the clutch determines the power of the motorcycle, so it needs to be adjusted regularly for maximum power transfer. A clutch can be in perfect working condition and not deliver maximum power to the gearbox sprocket until it is adjusted correctly. Wear and tear over time and a few other factors can necessitate clutch re-adjustment.
How Does A Motorcycle Clutch Work?
Basically, a clutch consists of 2 circular plates that rub against each other. A set of springs maintains the pressure to keep the plates together. One plate is connected to the engine and the other plate is connected to the gearbox. When the rider pulls the clutch lever, the springs are compressed and the plates move apart, thus disengaging the engine from the gears.
At this time the rider can change gears. If the clutch is wrongly adjusted and the clutch cable has too little slack, then the clutch plates will not separate correctly, resulting in low power transfer from the engine to the wheel. If the clutch cable has too much slack, then the clutch plates cannot disengage completely making it difficult to change gears.
When the clutch has been correctly adjusted, the clutch plates can be fully engaged, allowing maximum power to be transferred from the engine to the wheel. When the clutch lever is pulled, the clutch plates separate allowing the rider to change gears easily.
What Causes Late Motorcycle Clutch Engagement?
Late motorcycle clutch engagement can be caused by problems with the clutch cable such as too much slack, or even worn clutch plates and springs. While worn-out parts will need replacing, most clutch engagement issues can be fixed by adjusting the engagement point.
The clutch engagement point varies with the clutch used and the motorcycle model, but in general, a few millimeters can make a difference in how well the clutch engages. The first checkpoint is to see if your clutch cable has enough slack. If there is insufficient slack, the clutch lever will feel tight when you pull it.
The clutch plates need to engage fully for maximum power transfer to take place, so a clutch cable that has too little slack can prevent the clutch plates from coming together. The next possibility is that the clutch springs have lost their springiness and need to be changed. Clutch springs are cheap, so it is worth replacing them every few months when you’re changing your engine oil.
Types Of Clutch On A Motorcycle
Motorcycles use 4 types of clutches: wet, dry, hydraulic, and slipper clutch. Each one comes with its own set of advantages and disadvantages. The average motorcyclist will most likely use a wet clutch as the hydraulic and slipper clutches are found only on the more expensive bikes.
The Dry Clutch
The dry clutch is larger and noisier but has the distinct advantage of not losing power to fluid drag as in the case of the wet clutch. The lack of oil has the disadvantage of increasing the wear and tear on the clutch plates, requiring more frequent replacement. However, since the friction is much higher, the engine is able to transmit its torque to the wheel easily.
Without oil, the clutch plates heat up faster but are able to transmit more power. The dry clutch uses a single pair of non-perforated clutch plates that are larger in size compared to wet clutch plates. They are very easy to clean, if required, and provide very high friction.
Because of the performance benefit that a dry clutch offers, there are a number of motorcycles that use them. To increase the cooling, the side cover is taken off so that they are exposed to the oncoming wind but also has the issue of increasing the noise level massively.
The Wet Clutch
The wet clutch is smaller and is submerged in engine oil. Any heating of the clutch is removed by the oil which also lubricates it. Since the wet clutch is more efficient than the dry clutch, it is more popular and is used in most motorcycles. The downside to the wet clutch is the fluid drag as it is immersed in oil which uses up some of the engine power.
Since the clutch plates are submerged in oil, the heat generated by them is removed by the oil, permitting harder usage. They can take a lot of abuse and are easy to use making them the preferred choice for most motorcycle manufacturers. Wet clutches use multiple perforated clutch plates to overcome the power loss that results from being submerged in oil.
The operating and design cost of the wet clutch is higher, although its maintenance costs are low. The clutch plates are difficult to clean and are easily damaged, but compared to the dry clutch the wet clutch is completely silent. When the clutch slips they get overheated, thereby damaging the plates and rendering them ineffective very fast.
It is noteworthy that even today there are motorcycle manufacturers that prefer using dry clutches for their efficiency in power transfer. Ducati is famous for its dry clutch motorcycles, and even BMW has a few classic bikes that employ them. Every MotoGP bike uses a dry clutch. Of course, Ducati has constructed their reputation based on their racing success, so they continue to use dry clutches.
The regular sports motorcycle enthusiast will probably never encounter a dry clutch because most sports bikes use only wet clutches. A sports bike doesn’t need the high power that a dry clutch provides, and cost constraints, as well as other limitations, make the use of wet clutches the norm.
The Hydraulic Clutch And Its Advantages Over A Cable Clutch
The main difference between the hydraulic clutch and the 2 other clutches described earlier is how it is actuated. Wet and dry clutches use a Bowden cable to transfer the force applied to the clutch lever to the clutch plates. A Bowden cable is a flexible, usually multi-stranded wire that moves inside a plastic sheath.
In the hydraulic clutch, fluid is used to transfer the force applied by the clutch lever to a slave cylinder that puts pressure on the clutch plate. The big advantage of a hydraulic system is that it adjusts itself as the clutch wears down, making constant adjustment unnecessary. This has a few advantages when compared to a cable.
How It Compares With A Cable
The clutch cable needs to be lubricated periodically and snaps very often at the clutch lever exit point despite liberal amounts of grease and oil applied. On the other hand, the hydraulic clutch only needs to have hydraulic fluid in its reservoir for it to work. It’s also smoother because of the master cylinder and slave cylinder which work to amplify your grip strength.
However, the hydraulic system is more expensive to set up and repair when a hydraulic seal fails. Of course, every few years the hydraulic fluid needs to be replaced. but it still is far superior to a cable clutch. The problem with brake fluid is that it is hygroscopic, meaning that it absorbs water from the air if it gets a chance which degrades its performance.
The force applied by the clutch lever to a hydraulic clutch goes to a piston in the master cylinder which transfers the force to the slave cylinder that moves the clutch plates. For bikes that have a cable clutch but want a hydraulic clutch, there are conversion kits being sold that allow you to fit a hydraulic clutch to your motorcycle.
These hydraulic clutch kits are priced at about $40 to $80 and are complete with instructions on how to install them. Installation is very simple and only takes a few minutes before the rider can use it. They are pre-bled and use mineral oil instead of brake fluid, which means that the fluid never has to be replaced and is not hygroscopic.
The Slipper Clutch
The slipper clutch is found on high-end motorcycles and is also known as a back-torque limiter. Bikes on the race track use them as they are best suited to performance motorcycles. They are designed to prevent the engine from over-revving if the rear wheel hops. This happens when the rider brakes hard suddenly. At this time, the clutch slips until the engine speed matches the bike speed.
If the clutch did not slip, then the rear wheel would try to drive the engine faster than it is running. If the rear wheel tries to drive the engine, it loses traction on the road which can lead to a fatal accident. Instead, the slipper clutch comes into play to absorb most of the backdrop torque, proving why it is called the back-torque limiter.
Its biggest advantage is that it prevents the rear wheel from locking up if the engine seizes. Slipper clutches have been used on automobiles and on experimental aircraft.
Torque vs RPM
Torque is the turning force of a rotating shaft and rpm refers to the number of revolutions per minute that the shaft rotates. If you have ever used a battery-operated fan, you may have noticed that the fan blades are fixed onto the shaft of a small 3-volt or 6-volt electric motor. Switch on the fan and try to stop the motor by holding the shaft of the motor between your fingers.
It is very easy to stop the motor because the torque generated is very low. A small electric motor’s shaft rotates between 1,000 rpm to 4,000 rpm depending on the make. If the same small motor is connected to a gearbox and geared down, its output shaft will rotate at 20 or 30 rpm depending on its application.
Hold the output shaft between your fingers. This time you will find that it is very difficult to stop the motor shaft from rotating because of the force with which it rotates. The torque has been multiplied by gearing it down to a much lower rpm. The same principle applies to an internal combustion engine that uses a gearbox to reduce rpm and increase torque.
The Torque Curve
There is something called a Torque Curve that projects the torque increase with respect to the decrease in rpm. Exactly why torque increases as rpm decreases is beyond the scope of this guide, although it may be worth reading about the Torque Curve to find out more about it.
The Gearbox Determines The Torque And RPM
The motorcycle engine shaft is connected to a series of gears to gear down the rpm to the level required to drive the load. This is achieved by shifting into the appropriate gear. High torque is needed to move a motorcycle from a halt, and lower torque with high rpm is needed to increase its speed after it has started moving.
Once the correct gear has been shifted into, the power output from it is connected by the clutch to the gearbox sprocket to drive the rear wheel. Clutch inefficiency results in lower torque transferred to the gearbox sprocket with correspondingly lower bike speed and degraded fuel efficiency. Many new riders try to move the bike from a halt using the wrong gear and experience the engine stalling.
This happens when the torque output from the selected gear is not enough to power the bike with its load forward. The opposite is also true. A rider who tries to increase speed by shifting into a gear that imparts high torque with low speed will find that the engine is revving up but the bike isn’t moving accordingly.
2 Steps To Adjust Motorcycle Clutch Engagement Point
1. Adjust The Barrel Adjuster
If the power from the engine doesn’t quite seem to be reaching the wheel, then some clutch adjustment may be needed. At the end of the clutch lever, there is a barrel adjuster that can give or take up slack in the clutch cable. If this fixes the problem, well and good, but if not, then the clutch engagement arm needs adjusting.
Before adjusting the clutch screw or locknut, turn the barrel adjuster at the clutch lever so that it goes fully into its perch. Failing to do this can make the clutch adjustment difficult, as it is taking up slack in the cable that is needed for correct clutch engagement.
2. Adjust The Angle Of The Clutch Arm
The clutch cable goes to a clutch arm. The cable has to make an 80 to 90-degree angle with the arm for correct functioning. Below the engine is a clutch adjustment screw with a locknut. First, loosen the locknut then use a screwdriver to open the screw.
This needs to be adjusted very slowly as even a quarter turn can make a difference. Once you have completed the adjustment, start the engine and check if the clutch is engaging. If not, open the screw another quarter turn and check the clutch engagement again. More than a half-turn adjustment is rarely needed. Once you have set the clutch to your satisfaction, remember to tighten the locknut.
If you cannot find the clutch arm or the clutch adjustment screw, then refer to your motorcycle service manual for instructions on how to adjust the clutch. Unless your clutch plates are badly worn or clutch springs need replacement, adjusting the clutch is very simple and can be done in a few minutes at home requiring a minimum of tools.
There are variations of the clutch adjustment screw and locknut, but this is the key setting that controls the clutch engagement point. The instructions here are general, although they can be applied to almost any motorcycle that uses a wet clutch. In case of any doubt, consult your service manual before loosening any nuts or screws.
Adjusting your motorcycle clutch so that the rear wheel gets all the drive from the engine is very easy to do and can result in satisfying performance increases. Other benefits include improved fuel efficiency and money saved from replacing worn parts, which makes it a skill worth learning.