How to remove the variator on a chainsaw

How to remove the drive sprocket from a chainsaw and replace it with a new one yourself

The chainsaw sprocket is used to transmit engine torque through a centrifugal clutch to the saw chain. The sprocket teeth are highly stressed during operation and will gradually wear out. To remove the chain saw chainwheel is easy to do with a special tool, but it can also be done with a handy tool.

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When and why you need to replace a worn chainsaw chain sprocket

The chain saw or electric chainsaw drive sprocket is one of the most important parts of your saw. The chain saw chainwheel’s main function: to transmit engine torque to the saw chain. This transmission is made through a centrifugal clutch. Saw chain sprockets can be categorized as professional or consumer sprockets, just like chains. As you use your chainsaw and cut wood, the drive sprocket. like the chain. will gradually wear out.

Husqvarna chain sprocket

Let’s learn more about why you need to replace a worn chainsaw or electric chainsaw sprocket and when it’s best to do so.

Here are some general warning signs that the sprocket needs to be replaced:

  • Your chain saw has been changed twice (one of the rules for chain saws and electric saws is that if you use the tool frequently and actively, you should change the drive sprocket after two chain changes)
  • cutting quality has deteriorated and the chain needs tightening more often;
  • you installed a new chain, to which the old drive sprocket does not fit (this part is not universal, and also has its own pitch, in addition, the steps of the drive and driven chain sprockets must match, otherwise the tool will not work);
  • you use a different bar, a shorter or longer one.

How to remove and replace the chain sprocket on a chainsaw?

Many gasoline chainsaw owners are concerned about how to remove a chainsaw sprocket after it has broken.

When replacing the sprocket, all work must be done carefully and with care.

The chainsaw is designed as a classical mechanism, which is driven by the internal combustion engine. The design of the unit uses one of the most simple single-cylinder two-stroke carburetor engines, which run on gasoline.

The simplicity of the chainsaw engine and overall design ensures that the chainsaw can operate reliably in harsh conditions. Low knowledge and skill requirements for chainsaw operation.

The only prerequisite for continued, trouble-free use is regular inspection and maintenance of the implement. You should replace worn components while you operate your chain saw.

To reduce wear on the saw chain, check the chain lubrication, chain tension, chain wear, and drive sprocket.

Know your chainsaw’s design before you attempt to repair it. To replace an essential component, the drive sprocket, you must learn how the clutch on the attachment works.

The design of the unit clutch

Chainsaws are machines fitted with drive sprockets which form an integrated unit with the clutch basket.

The clutch operates automatically depending on the engine speed.

The units are equipped with a centrifugal type clutch, which operates in automatic mode, depending on the number of engine revolutions.

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When the machine’s engine is running at idle or low speed, the friction plates in the clutch basket have a certain amount of freedom in the radial direction.

The freedom of movement results in the elements being drawn to the center of the rotary shaft by the action of the springs and does not transmit any rotary motion to the sprocket drum.

How to Easily Remove a Chainsaw Flywheel

As the engine speed increases, the centrifugal force exceeds the force of the springs, which causes the elements with friction pads to move. These elements are pressed against the inner walls of the drum by centrifugal force.

This contact transmits rotary motion to the drum and sprocket that drive the saw chain of the tool. The chainsaw sprocket can be located either outside the tool or under a special cover that protects the mechanism from damage and the device operator from injury.

The main advantage of this type of clutch is that when the saw chain jams, the elements with friction pads slip, which protects the internal combustion engine from serious damage.

The main reasons for replacing the drive sprocket

The Allen wrench is the primary tool you will need when replacing a sprocket.

The most common reasons that force a tool repair involving the replacement of a drive sprocket are:

  • Chain jamming due to defects in the machine’s operation;
  • High sprocket wear as a result of prolonged use of the unit.

If the implement is used frequently, there is increased wear on the drive sprocket as a result of the increased stresses placed on the sprocket when sawing wood. There are two ways to operate the unit:

In the first type of operation, the chain is operated until it is completely worn out. There are several disadvantages to this method. The main one is the problem of checking the wear during intensive machine operation.

If two or more chains are used in the process, the wear on the chains and sprocket is evenly distributed, so that the unit will be in service longer before a repair consisting of replacing the sprocket.

In addition to sprocket wear, the bearing in the sprocket should not be forgotten. This component works at all engine speeds. If the sprocket is replaced, the bearing has to be replaced at the same time.

Complete clutch and sprocket should be replaced on time.

If repair work is not performed in time, increased vibration and wear of bearings installed in the internal combustion engine on the crankshaft halves will occur during operation.

Maximum depth of sprocket teeth wear should not exceed 0.5 mm. Sprocket life is twice as long as a single chain, so you should use two chains. Replace chains and sprocket at the same time when the chain reaches the end of its service life.

Algorithm of carrying out replacement of a clutch drum

Regular inspections are necessary for continued chain saw use.

When replacing the clutch drum, you should use only a strictly defined type of design element of the device. When replacing the drum, replace the bearings of the structural element at the same time.

To perform the repair work, you need to buy a special repair kit that includes a driving sprocket and a bearing. After buying a repair kit you should prepare the necessary materials and tools for the repair. The basic tools that will be required when conducting the repair are as follows:

Clutch replacement

When replacing the clutch, we do not recommend the use of metal or plastic objects as a stopper. The former can scratch the cylinder, the latter can litter it.

  • Engage the chain stop brake, remove the protective cap and remove the saw headset;
  • Remove dirt, sawdust, dried grease, if any;
  • Remove the air filter and glow plug;
  • Unscrew the spark plug by means of a spark plug wrench;
  • Rotating the crankshaft, bring the piston to the upper point, then withdraw it by 6-9 mm;
  • Stop the piston in its upper position with a 7-8 mm rope;
  • We use a special wrench to unscrew the nut on the clutch.
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Most chain saw moving parts are right-handed. That is why the nut on the clutch has a left-hand thread. To remove the cover turn the wrench clockwise. It is forbidden to perform this operation with a hammer and chisel. you will break the edges!

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  • Remove cap and drive sprocket. Diagnose malfunctions and evaluate the wear of parts. Evaluate the condition of the needle bearing;
  • If necessary, we carry out replacement of parts for new ones (most often it needs a leading star);
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To assemble the chainsaw clutch you have to follow the reverse order, but you have to pay attention to some peculiarities.

The nuances in the installation of the clutch system:

  • On some chainsaw models there may be a washer between the drive sprocket and the clutch. Pay attention to which side to the engine it stands;
  • Some oil pump drives have a special spring (whisker) which is responsible for transmitting the rotational motion from the drive sprocket to the oil pump. It is important to adjust the spring so that it is in the proper slot on the sprocket housing at the free end (whisker). Otherwise the saw headset will not lubricate;

Important: after disassembling and reassembling the clutch, be sure to check the automatic oil feed system.

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Troubleshooting and Repair

Chainsaw clutch repair with your own hands is carried out only in special protective clothing: mask and goggles.

Main malfunctions, their causes and remedies:

  • If the chain train keeps turning when the engine is not running smoothly. It can be caused by a failed spring. If this is the case, we recommend that you replace the damaged mechanism with a new one.
  • Unusual noises can be heard as the chain moves. This problem could be related to an overheated cam or a broken spring. The system should be inspected externally and all worn elements should be replaced.
  • If the failure is due to the fact that the coupling device frequently slips, it is necessary to replace the mechanism completely.

Variator Nut Removal Tips.MP4

How to extend the life of a drive sprocket?

Experienced sawyers recommend working with several of the same blades, changing them as the links become dull. This technique can significantly reduce pinion wear, but certainly can’t prevent it completely. Sooner or later it will have to be removed and replaced.

Drive components are made of extremely hard, high-alloyed alloys in an industrial environment. They are also given special treatments to improve their strength, wear, and corrosion resistance. These can include:

You cannot duplicate this process in your own home workshop. Attempting to restore by surfacing followed by milling to size will not work either. Such a remanufactured pinion will last several times less than the original one. The cost of repair kits is incomparably small compared to the wasted effort and time.

Part replacement in service shops is expensive, so it’s smart and economical to change it for a suitable industrial pinion by yourself.

How to remove the clutch on a chainsaw: step-by-step instructions, recommendations for different models.

The clutch is one of the main mechanisms of modern chainsaws. It is required to transmit torque to the saw chain sprocket and protects the motor from overloads and breakdowns. Over time, this element will require scheduled preventive cleaning or even replacement. It is also possible to remove the clutch at home. To do this you must have a basic understanding of how it works and the construction of the saw model in question.

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All chainsaws of the latest generation are equipped with a centrifugal-type clutch mechanism. Clutch transfers torque from the engine crankshaft to the saw head. The element operates exclusively in automatic mode, which prevents excessive stress on the internal combustion engine. The main elements of the clutch:

  • Drum. Can have a removable or fixed sprocket; it is a transmission mechanism.
  • Friction plates (counterweights). They are moved by centrifugal force, there is always a smooth connection to the drum.
  • Springs. They ensure a firm grip on the crankshaft.

When the chainsaw starts, the crankshaft is in motion. The clutch is attached to it, from which the chain drive sprocket moves away. Friction pads are clamped in idle mode so that the torque is not transmitted to the drum. Once the revolutions are increased, they move and drive the rotating sprocket.

Important! Professional models have a drum with fixed sprockets. This increases its wear resistance, but increases the cost of repair.

Design and operation of the chainsaw clutch

Modern chainsaws are equipped with a centrifugal clutch. This means that their operation depends entirely on the torque of the motor, which at a particular moment in time is produced by the saw.

Its main structural elements are:

The principle of operation is as follows. When starting the saw, elements that move freely in a radial direction are pulled to the shaft axis by springs. In this case the torque is not applied to the drum, and therefore to the sprocket and guide. The moment centrifugal force takes precedence over the force potential of the springs, the clutch elements loosen and compress around the interior of the drum causing it to torsion. It causes the rotation cycle to shift to the chain sprocket and the bar chain itself.

The main advantage of this type of clutch is its slippage during sudden braking of the cutting part, which does not stop the engine. As a result, the “heart” of the saw. the motors remain intact.


Speaking of chainsaws, it is impossible to ignore such an important device of a chainsaw as a carburetor that ensures reliable engine operation along with the ignition. It controls the quality of the fuel-air mixture that makes the chainsaw easy to start and the power and stability of the chain saw. Chainsaw manufacturers prefer to use carburetors from well-known brands like Walbro, Zama and others.

Chainsaw carburetor. Upper arrow. fuel hose, lower arrow. throttle actuator.

Chainsaw carburetor. Arrow. throttle valve actuator cable.

chainsaw carburetor. Arrow. fuel hose.

Below is a diagram of another chainsaw carburetor.

Carburetors have a throttle valve that allows the mixture to be leaner or richer depending on operating conditions. There are several screws for fine tuning, which can be used to adjust the low and high RPM, as well as the idle speed. An air filter is installed on top of the carburetor to clean the air that enters it.

Chain brake adjustment

The chain brake often does not work because the brake band and the space under the cover is clogged with grease or sawdust. All parts should be clogged. It is possible that the belt is simply worn out, in which case it must be replaced.

Chain brake operation can be restored by mechanical cleaning

Some chain saw parts wear out quicker than others. These include the drive sprocket, guide bar, chain, anti-vibration elements. For quick replacement parts, it is best to always have them on hand. You should not neglect the sharpening of the chain as well.

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