Replacing a worn chainsaw sprocket

When and why do you need to replace a worn chainsaw sprocket?

The drive sprocket of a chainsaw or electric saw is one of the most important parts of the sawing machine. The main function of the chainsaw sprocket is to transmit engine torque to the saw chain. This transmission is carried out through a centrifugal clutch. By type, sprockets can be divided into professional and household, just like chains. During the operation of the chainsaw and sawing wood, the drive sprocket, like the chain, gradually wears out.

Husqvarna drive sprocket

Let's find out in more detail why it is necessary to replace a worn chainsaw or electric saw sprocket and when is the best time to perform such a replacement.

The main signs that the sprocket needs to be changed:

The chain on your chainsaw has been replaced twice (one of the current operating rules for chainsaws and electric saws is that if you use the tool frequently and actively, after two chain changes you should replace the drive sprocket);
the quality of sawing deteriorated, the chain began to need tightening more often;
you have 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 pitches of the drive and driven chain sprockets must match, otherwise the tool will not work);
you are using a different tire, shorter or longer.

Video about replacing a sprocket on a chainsaw:

When to change a chainsaw sprocket?

The following signs may indicate to the operator of a chain garden tool that an urgent replacement of the sprocket on a chainsaw is necessary:

unstable rotation of the cutting chain - the headset can rotate at variable speeds - sometimes faster, sometimes slower. In this case, the operator himself does not perform any actions with the accelerator;
extraneous noise during chain rotation - it can come from both the headset and the clutch itself. In addition, sounds can come not only while the chain is passing a certain section of the bus, but also in its different positions on the guide;
curved cutting line - when working with wood, the chain on the tire of a gas-powered tool can arbitrarily change its position on the trunk - it can move away from the original axis by a distance of 0.2–20 mm;
the formation of blue or red areas on the guide - if visible colored areas appear on the bar during sawing wood, it means that it regularly overheats. In this case, you will need to urgently replace the clutch sprocket.

Another reason to replace the sprocket is its wear. The uneven length of the teeth, as well as their unequal distance from each other, will tell the operator about the development of teeth. To notice a defect in a part, you will need to disassemble the coupling from time to time for routine inspection and cleaning.

Why do you need to replace the sprocket?

A worn sprocket must be removed for the following reasons:

with an old sprocket, the saw chain will stretch very quickly - after just a few uses the chain will hang, and tensioning will not help;
if you put a new chain on an old sprocket, the smoothness of the chain will decrease, the quality of the cut will deteriorate, the chain will lead to the side when cutting;
the general wear and tear of the chainsaw will accelerate, the tool may fail at any time;
The chain may break or the chain will jam during operation (danger of hand injuries and damage to the body of the electric saw or chainsaw);
the tire will heat up faster, which will lead to rapid overheating of the chainsaw;
the load on the engine and body will increase.

Important! You cannot change sprocket sizes at your own discretion during repairs; use the manufacturer’s standard. Unauthorized replacement will lead to deterioration in the technical performance of the chainsaw or electric saw.

Video on how to change the sprocket on a chainsaw:

How to choose

When it is necessary to select the optimal chain pitch for a chainsaw, it is best to take into account the manufacturer’s recommendations and, based on them, select the type of saw attachment.

If the manufacturer's recommendations are not known, then you need to choose based on engine power. We have provided the recommended values corresponding to a specific step just above.

Important! When choosing, do not forget that the distance between the links is not the only parameter that you need to pay attention to.

It is also worth selecting the thickness of the link, the type of cutting tooth, and the number of links. Productivity largely depends on the sharpening angle, depth of cut and shape of the stopper tooth. The sharper the limiting tooth, the higher the cutting speed and the lower its quality.

Below we suggest watching a video about choosing a chainsaw chain pitch. The video explains and shows how to determine it, for which chainsaws, and what chain pitch to use.

Are there ways to extend the life of an existing sprocket?

The main ways to extend the working life of a chainsaw drive sprocket:

use several chains (preferably three). This method is the most gentle and convenient for the chainsaw owner in that there is no need to constantly tighten a chain worn out by intensive work. Operating three chains in turn will save the life of the sprocket and delay its replacement;
high-quality maintenance of the drive sprocket bearing. This part plays an important role in the functioning of both the drive sprocket and the engine. For lubrication, it is recommended to use a special lubricant. The sprocket bearing is not constantly engaged, but only at idle speed, and therefore requires periodic lubrication. You can use a tire nose lubricant, such as standard lubricant from Repsol or Husqvarna.

Chainsaw drive sprocket design

The design of the chainsaw has not only a driving sprocket, but also a driven sprocket. The driving sprocket of the chainsaw is located in the design of the tool, and the driven sprocket is located at the end of the bar. The purpose of the driven device is to equalize the tension and direction of movement of the chain device.

Driven star on tool bar

Leading devices can be solid or prefabricated. Solid products consist of a hub with a pressed-on gear ring. When replacing, the entire mechanism assembly is dismantled, since the gear structure is one-piece. Chainsaws of many well-known brands are equipped with solid gears from the factory.

What does a solid gear look like on a chainsaw?

Collapsible products are more advanced, since the process of replacing them is simplified through the simplest mechanism design. Only one crown is replaced, the cost of which is 2 times less than the prefabricated mechanism. The appropriate wear of gear teeth can be determined by the following signs:

The presence of large radii at tooth transition points
Uneven tooth width
Detection of chips and metal shavings on the top of the teeth
Scores and marks on the inner surface of the holes in the hub
When starting the tool, chain jamming is detected

When the master device wears out, it must be replaced. You can do this yourself, for which you initially disassemble the tool and determine the version of the installed device. Even if a non-separable gear is installed on the tool, then instead of it you can install a prefabricated mechanism, which is more rational.

Collapsible gear type for chainsaw

There are two types of installation of leading stars on chainsaws. The first method involves placing the gear on the outside. Such designs are the most common on Stihl chainsaws. The design of such a device is shown in the photo below.

Non-separable type product on the tool

The second option is typical for instruments of Chinese origin. The gear teeth are located not on the outside, but on the inside, that is, the device is located in reverse.

Star design on a Chinese chainsaw

Depending on the design of the tool, the process of dismantling the products in question will differ.

This is interesting! To extend the life of the chainsaw drive gear, it is necessary to run-in the tool and not overload it during operation, which depends on the purpose (household, semi-professional or professional). You can cut down a tree with a household tool, but the saw is not intended for this, and its frequent use with overloads will lead to wear of the component parts.

What tools are needed to replace the sprocket?

To replace the drive (drive) sprocket you will need the following tools and components:

a special key for removing this part (usually supplied with expensive branded chainsaws; cheap saws are not equipped with such a key);
a drift made of aluminum or copper (only from soft metals and only in the absence of a key);
hammer (for striking the drift while unscrewing the sprocket);
flat screwdriver for tightening the nut;
sprocket bearing grease.

Design problems, differences between different models

Branded chainsaws have a special design that does not allow replacing a worn drive without removing the clutch and other parts of the chainsaw. That is, the saw needs to be almost completely disassembled. More modern models of expensive chainsaws are always equipped with a special key.

Replacing a sprocket on a chainsaw

Also, the owner of a chainsaw may encounter the following nuance: on Chinese imported chainsaws or electric saws, the sprocket on the clutch mechanism may be located in an unusual way. On older models, when the chain teeth wear out, you need to unscrew and replace the one-piece drum with the drive. On newer models, the sprocket can be replaced separately.

Algorithm for self-replacement of the clutch drum with sprocket

How to replace the drive sprocket on an electric saw or chainsaw - more on this below.

To replace the sprocket, you need to do the following:

remove the chain brake cover and pull it towards you (avoid contact of the brake band with the clutch parts);
using a wrench, loosen the nuts holding the chain tension and the chainsaw cover;
remove the chain and then the bar, removing debris and sawdust from the mounting holes;
we fix the piston in the cylinder using a regular cord, but if possible, you need to use a piston stopper or a special lock;
the clutch begins to rotate and does this until the piston touches the exhaust port;
after which the stopper or cord is lowered into the candle opening and fixed there by tying several knots (the stopper will fix itself);
unscrew the clutch nut (note that the thread of this nut is left-handed, take this into account when unscrewing);
It is prohibited to use hard tools so as not to break the soft metal of the clutch nut;
then the clutch is removed;
then remove the sprocket gear itself;
replace the old sprocket with a new one;
Reassemble the structure in reverse order.

How to replace a star on a Chinese chainsaw yourself

If you come across a tool where the star is placed on a thread (fixed instead of a bracket), then the replacement process will be somewhat labor-intensive. Let's consider the sequence of actions in order:

Initially you need to remove the casing, as well as the bar and chain, as in the first case
After this, the protective cover is removed, under which the air filter and spark plug are located.
The spark plug should be unscrewed. You need to screw either a special plastic insert inside the cylinder, or insert a cord. This is done in order to block the movement of the piston. The cord used is wool without any protruding wire. The best option for such purposes is a wire from an iron
Preference is given to the second option, since plastic inserts can damage the piston structure. The cord is inserted into the cylinder when the piston does not reach 2-3 mm from TDC
When the movement of the piston is blocked, you should use a special key, which is usually supplied with the tool. If there is no such key, you can use one that is designed for angle grinders or a regular open-end one at “19”
You need to rotate the device to the side in a clockwise direction. Once the fastening is loosened, you can unscrew the device by hand, remove the gear and replace it, and install all the parts in place in the same way

Finally, when the star is fixed, the cord is removed from the cylinder and the candle is installed in place. A detailed description of the dismantling process is presented in the video.

After the work has been done, you will need to adjust the chain tension and check the tool in action. At this point the replacement process can be considered complete. How to replace a chainsaw sprocket and what this procedure is is described in detail in the material. If you encounter various problems, then seek help from specialists who will help you understand the situation free of charge.