The clutch is an integral part of a kart’s engine. Unlike in a car, there is no clutch pedal in a go-kart so you might think that it is not as important as in a car. However, the clutch is crucial, and it does wear over time, so it’s useful to know how to check and replace your go-kart’s clutch.
Here is how to check and replace your go-kart’s clutch:
- Remove the engine from the chassis
- Put the crank locking tool in place
- Use a spanner to remove the retaining nut
- Remove the retaining washer and the clutch drum
- Replace the clutch drum (if needed)
- Remove the O-ring and washer that holds the clutch shoe in place
- Undo the bolts that hold the clutch shoe in place
- Remove the clutch shoe
- Replace clutch shoe if necessary
- Reassemble in reverse order
It’s important to check your clutch regularly. While it can last a long time, once cracks begin to appear it’s best to replace it as soon as possible since these will cause the clutch to wear out much faster. Before we discuss how to replace your kart’s clutch, let’s go over why it’s so important.
Why Is A Go-Kart’s Clutch Important?
The clutch is a small part on the exterior of the kart’s engine. You can only see the clutch drum, which is the outside casing, or housing, of the clutch. The clutch is connected to the chain, and it holds the front sprocket. The front sprocket is the smaller of the two, and it will likely have between eleven and thirteen teeth.
The clutch is crucial to your kart because it is what transfers the power from the engine into drive. Essentially, the clutch is used to create the energy that turns your kart’s wheels. Therefore, without a clutch your kart will have no drive.
How A Kart Clutch Works
The actual clutch is found inside the housing, and unlike the one found in a car, it is a centrifugal clutch. This means that the ‘shoe’ found inside the clutch housing spins and generates centrifugal force which generates the power to turn the wheels. We will go into more detail on how all of this works later.
Centrifugal clutches are more sensitive than a normal clutch, and if too much pressure is put onto them, they can easily break or even begin to melt. Therefore, it is crucial to check your clutch regularly and ensure that there is no damage.
A damaged clutch can cost you horsepower. In a go-kart engine that only has around 30 horsepower, every horse counts! So, you do not want to be losing power through a damaged clutch.
While you might think that there is another problem such as jetting or perhaps you’re using the wrong sprocket, you might overlook the servicing of your clutch. It is not always the case, but if nothing seems to be working, doing a quick inspection on the clutch won’t do you any harm.
How Is It Different From A Car’s Clutch?
A go-kart’s clutch is significantly different to that of a car. Firstly, the car is able to engage and disengage the clutch through the use of a clutch pedal. When the car is moving, the clutch is engaged. When the clutch pedal is pressed, the clutch disengages.
When a clutch is disengaged, the operating arm pushes a release bearing on the clutch which releases the pressure on it. Most clutches operate through hydraulics or a cable which connects to the third pedal in the cockpit of the car.
A go-kart on the other hand does not have a clutch pedal, just a throttle and a brake, yet it still has a clutch. You might be asking yourself how this clutch is able to work without a pedal. Karts use a centrifugal clutch which is able to engage and disengage by itself depending on the number of revolutions that are sent through the engine.
Why Do Go-Karts Use A Centrifugal Clutch?
Go-karts use centrifugal clutches because they are simpler and much less expensive than a normal clutch. However, the majority of karts are also direct drive, which means that the clutch does not need to disengage to change gear at high revs, making a normal clutch pointless.
This cost-effective clutch is also ideal for entry-level motorsport series, and its simplicity to service and repair means that it is a beginner friendly option for those who are not mechanics and are just starting out in motorsport.
The entire clutch unit for a Rotax Max kart costs around $400. However, it’s highly unlikely that you will need to replace an entire unit. The highest wearing parts are the clutch drum which costs around $50 and the clutch block (also known as shoes) which costs about $130.
How The Kart’s Centrifugal Clutch Works
As the name suggests, the clutch uses centrifugal forces in order to generate ‘power’ that is pushed onto the chain and then onto the rear axle. Since the clutch is essentially just a round disc, the weight is pushed to the outside of the shoe and into the clutch drum.
Inside the engine you will find the engine shaft, which has a weight system on it. When the engine is on this weight begins to spin, starting the centrifugal motion in the clutch. The faster the weight spins, the higher the revolutions of the engine.
Once the revolutions reach a certain point, in most cases between 2000 and 3000 RPM, the centrifugal motion inside the clutch creates more pressure, leading it to engage the clutch and start the motion of the sprockets and the wheels.
It’s a complicated process, but what you need to know is that the clutch relies on motion in order to keep the engine running. The clutch shoes inside the drum have small cut-outs on them which help to transfer extra weight into the clutch drum, making it spin.
You’ll notice when your kart is idling, it normally idles at a higher RPM than your average car. It will idle anywhere under 3000 RPM, and while this is enough for some cars to change gear, this is where most go karts will begin to move. Your kart will rev up to 12,000 or even 13,000 RPM.
The centrifugal clutch will only engage when the revolutions reach a high enough point, whereas a normal clutch found in a car can generate motion at lower revs, in some cases under 1000 RPM. This is why the idling revs of karts are so high.
How To Identify Damage To The Clutch
If you never open or inspect your clutch, you’ll never know the true extent of any damage or levels of wear that are on it. However, there are some tell tale signs that your clutch is worn out and is in desperate need of replacement.
The first sign is that your kart is unable to idle. In most cases, this is due to severe wear on the clutch, and you will most likely find the clutch shoe in pieces or severely cracked once you open up the clutch drum.
A weakened clutch shoe will mean that the clutch is not able to produce enough force to keep the engine running at lower revs, so when you try to idle your kart, it tends to just cut out completely. A kart should be able to idle on its own, without touching the throttle at all.
If you find your engine cutting out when the revs drop below 2000-3000 RPM, you should check out the state of your clutch. If the clutch shoe is completely broken, the pieces can jam the clutch drum and prevent it from keeping the engine idling.
Lack Of Power
Another sign that your clutch might need replacing is a lack of horsepower. When your clutch is damaged, it can struggle to send the power from the engine through to the wheels. It can be difficult to tell when your kart is low on power.
However, in most cases a lack of power will make quite a significant difference to your acceleration out of corners and your overall top speed. This will be obvious when you are racing against other competitors whose karts will be significantly faster than yours out of slower corners and on the straights.
If your clutch shoe is shattered, you will also hear a mechanical rattling noise when the engine is running. You can hear this best from the outside of the kart when the engine is running at lower revs. The best way to identify this is to put the kart up on a stand and rev the engine.
While the engine is revving you will hear the distinct mechanical clanking noise, as if you were to take pieces of metal and shake them around inside a tin can. This is the sound of the loose metal pieces of your shattered clutch shoe rattling inside the drum.
Signs Of Wear On The Clutch
You can identify damage to your clutch by actually looking at it as well. This is not the easiest thing to do since it might require you to remove the engine from the kart. You don’t always need to, but it can make the entire process much easier.
Removing the clutch will give you a better idea of the extent of the damage done to it. Firstly, you will need to check the clutch shoe, which you will find inside the drum. The shoe will show some signs of wear in the form of cracks which will begin to appear.
These cracks will run as an almost straight line from the inside circle all the way to the outside edge. They will form in threes around the circular shoe, and they tend to split between the cut-outs, which is where most of the energy transfers through.
Normally when one appears, more will follow very soon. You can still run a shoe that is cracked. However, it will definitely need to be replaced soon, so you need to be prepared for that before it breaks.
If there is only one crack in the shoe, it’s only lightly damaged, and you can still use it. Once you see two cracks appear then it becomes a bit more urgent. A third crack means that it is on the verge of breaking, and you should have a replacement ready at the very least.
The next area where cracks will form is on the clutch drum. These are easiest to see on the inside of the drum, so it will need to be removed from the engine for close inspection. Due to the amount of grease and oil build up inside the drum you will need to clean it out before you check for any damage.
Since the front sprocket is located on the clutch drum, you will also need to check the wear on that. The front sprocket is crucial in the system that transfers engine power to the wheels. It’s the next step in the process after the clutch.
The front sprocket has teeth just like the rear one, except it will have much fewer teeth, in most cases between eleven and thirteen teeth. Wear on the front sprocket comes in the form of metallic shavings.
When the teeth are worn out, they become sharper and thinner, and this will cause the chain to slip under drive. When the chain slips then you will experience a loss of power and you will hear the engine revving higher.
It’s essentially the same as when the chain falls off a bicycle. The engine will rev higher because there is no longer tension on the front sprocket, and there will be no drive since there is no solid connection between the chain and the front sprocket.
Where Clutch Damage Comes From
There are a number of ways that you can damage the clutch on a kart beyond just the average wear and tear. Knowing what causes the damage on your clutch is important for making it last longer and getting the most use out of it.
Some drivers tend to rev their engines while keeping their foot on the brakes, and although this does help to warm up the engine, overdoing it can severely damage the clutch.
When you brake and rev the engine at the same time you are putting a huge amount of centrifugal force through the clutch, but the problem is that the force has nowhere to go since the wheels are not turning. Therefore, that force and energy is all pushed onto the clutch shoe, which is actually designed to move the energy onto the next part (the front sprocket), causing the motion of the wheels.
The clutch shoe is quite thin on a kart, and if too much energy is put through it, it can easily begin to crack and break into pieces. This is unlike a normal car’s clutch which is able to disengage on the driver’s command, so it will not do any damage to the cutch itself.
Some drivers also tend to ride the brakes and the throttle. This is a terrible habit to form, and it can be difficult to break. Doing so does not make you any faster, and it severely damages your clutch. You need to be either on the brakes or on the throttle, never on both.
Having an aggressive driving style is fine. It can be exciting and it might work for you, but mechanical sympathy is not something that is synonymous with aggression. You will be putting a lot of strain on your clutch.
Being quick on the throttle and brakes does not damage your clutch. What does damage the clutch, however, is riding the kerbs too much. Aggressive drivers tend to take a lot of kerb, and in some cases too much.
Taking too much kerb can cause the kart to catch some air, and the impact on landing can send shockwaves through the clutch which can damage it. In addition, this will cause strain on your rear axle as well, which could end up snapping in half.
Wear And Tear
The clutch will naturally go through some wear and tear during its lifespan. This can vary of course with the type of driving you’re doing. Centrifugal clutches can take a lot of strain but their lifespans are naturally shorter due to the high intensity work rate.
The clutch will begin to wear with heat, and as these are centrifugal clutches, they will naturally generate heat, especially when driving fast. With that being said, driving the kart slower will also damage the clutch since it won’t be able to engage fully.
Tools You Need To Replace Your Go-Kart’s Clutch
There are a couple of tools you will need to remove the clutch from the engine. However, the entire process is relatively easy and does not take long at all. It’s recommended you remove the engine from the chassis if it’s your first time taking the clutch off. It just makes the entire process much easier and gives you more room to work.
The tools you will need are:
- Front sprocket plate
- Crank locking tool
- Brake cleaner
- 17 mm ratchet spanner
- Impact wrench
- 38mm impact wrench socket
- Torque wrench (instead of impact wrench)
- 5 millimetre Allen key
- Clean cloth
Once you have all your tools you are ready to get started. If you are replacing the clutch shoes, clutch drum or the front sprocket you need ensure that you have the new parts ready as well. First of all, if you haven’t taken the engine off the chassis, you need to remove the chain from the front sprocket. Once you do that, you’re ready to start removing and replacing your go-kart’s clutch.
How To Check And Replace Your Go-Kart’s Clutch
1. Remove The Engine From The Chassis
The first step is to clean the back of the engine. You will see a ton of dirt and grease behind the radiator covering the engine and the clutch drum. The best way to get rid of this is to spray it down with the degreaser first and wiping it with the cloth. If there is some residual grease on the engine, use the brake cleaner and also wipe that clean with the cloth.
2. Put The Crank Locking Tool In Place
Once the engine is clean, you can start removing the clutch drum. The first step here is to place the Rotax crank locking tool. You will notice that it fits perfectly into the top right section of the ring gear. This tool will lock the crankshaft in place while you’re working on it.
3. Use A Spanner To Remove The Retaining Nut
Next, you will need your 17-millimetre ratchet spanner in order to loosen the nut that holds the clutch in place. It shouldn’t be too tight, and one turn of the wrench will loosen it enough for you to take it off with your fingers.
4. Remove The Retaining Washer And The Clutch Drum
When removing these parts, it is crucial to remember the order. The best way to do this is to place them down in a line as you take them out. The retaining nut is first, then the outside washer (there are two of these, and they are different).
Then, remove the clutch drum. There will be some dirt and grease inside the clutch drum which you need to clean out with your cloth. Wipe the inside the drum clean so that you can inspectit properly. At this point you can check for any cracks in the drum. They tend to form on the outside edges first.
5. Replace The Clutch Drum (If Needed)
This step is relevant if you are replacing your clutch drum. You will be removing the sprocket in this step and transferring it over to a new drum. You need to remove the nut on the inside of the drum. For this step you need the sprocket plates.
The sprocket locks into one of the cut-outs on the plate depending on the size of your sprocket. This holds the clutch drum in place while you undo the nut. You can use the impact wrench with the 38-millimetre socket to undo it, as this is the easiest way to undo the nut.
However, if you don’t have one of those, you can use a torque wrench. It will be more difficult though and you may need to use a vice grip or locking pliers to hold the plate. The sprocket may still be stuck inside the clutch drum, and if so you can use a small hammer to knock it out of the drum.
Reassemble the front sprocket to the new clutch drum and always ensure that you use some Loctite on the nut before you tighten it again. This one needs to stay in place under an immense amount of pressure.
You can retighten the sprocket nut with the impact wrench or torque wrench, and then it will be ready to go.
6. Remove The O-Ring And Washer That Holds The Clutch Shoe In Place
Next we will work on removing the clutch shoes. It’s held in place by another washer and an O-ring which you can simply pull off the bushing. Once again, remember the order that they are placed in. From the outside, it’s O-ring first and then the washer.
7. Undo The Bolts That Hold The Clutch Shoe In Place
You will notice three screws that hold the clutch shoe in place. You will need a 5-millimetre Allen Key to remove these. Undo each of them bit by bit before completely removing them, as you would with a wheel. The clutch shoe is essentially just a circular piece of steel with some cut-outs in it.
8. Remove The Clutch Shoe
To get the clutch shoe off the engine you can use a flat screwdriver to separate them by leveraging it behind the shoe. The shoe should come off easily and it most likely will not require a lot of force to remove from the engine.
9. Replace Clutch Shoe If Necessary
Once you remove the clutch shoe from the engine you need to clean it, once again using your brake cleaner and cloth to wipe all the grease and oil off. You can then begin to inspect the shoe for damage.
The general high-pressure areas are where the cut-outs are, and this is where cracks and chips will begin to form first. The cracks also tend to begin to form at the back of the shoe.
10. Reassemble In Reverse Order
Before you begin to put everything back together make sure that you give everything a good clean. From the clutch shoe to the engine cluster that holds the shoe. It’s best to use brake cleaner on all of these areas just to be safe.
Using oil can generate extra heat within the clutch unit itself and trap the hot air being generated. This will put more stress on the clutch and cause it to break or even melt while in operation.
Make sure you put Loctite on the Allen key screws before you bolt the clutch shoe back onto the engine. You can use the torque wrench to put these back and tighten them to 15 Nm. It’s best to use the torque wrench to ensure that you get equal tension on all three bolts.
Next up is the internal thrust washer and the O-ring, and then the clutch drum with your sprocket fitted. After that it’s the retaining washer and finally the retaining nut. Before putting the nut on, put a little bit of Loctite on the bushing. Once you do that, you’ve finished replacing your clutch.
Proper Clutch Maintenance
We recommend you service your go-kart’s clutch every 2 hours of engine running time. This varies from driver to driver, but it’s a good idea to check it out once a week. It’s a quick and easy job and it is absolutely worth it if you want to keep your kart’s engine running at maximum performance.
Removing the clutch drum assembly and the clutch shoe is a proper service, and you should be cleaning them and removing all the dirt and grease while you’re doing so. Inspect them for damage and cracks while you’re busy with it too. The more you do this the easier it becomes, and before you know it this will be a regular part of your routine that you can do in less than ten minutes.
Many people are afraid of working on their go-kart’s clutch. However, they do not realize how simple the process actually is. The clutch remains an important part of the engine which needs to be looked after very carefully. Just follow the steps above, and you’ll be checking and replacing your go-kart’s clutch with ease in no time!