A chainsaw requires regular diagnostics and periodic replacement of worn parts. With regular use, not only the saw set becomes unusable, but also the drive sprocket. In this tool, it acts as a clutch disc, which is why it bears a significant load both during startup and during operation. The sprocket on the chainsaw has a simple design, so repairs and maintenance are easy to do yourself. In this article we will look at how to determine the degree of wear of this part and carry out a planned replacement.
Drive star device on a chainsaw
Almost all models of modern chainsaws use a centrifugal clutch system. The specificity of this mechanism is that when the maximum number of revolutions of the gasoline engine is reached, the clutch drum starts automatically, transmitting rotation specifically to the drive sprocket. This reduces stress on the tool's underlying parts, extending tool life and peak performance.
Figure 1 – Diagram of the drive star device
The clutch drum, where the sprocket is located, can be located on the inside or outside of the chainsaw body. There is always a cover on top to protect moving mechanisms from dirt, sawdust and dust. The clutch itself is a metal disc located in the coupling drum. The entire mechanism is attached to the engine crankshaft with bolts and springs, along the edges of which there are friction linings. When the engine speed exceeds a certain value, centrifugal force occurs, exerting strong pressure on the inside of the drum. After this, the sprocket starts up and the chain saw begins to rotate.
Important ! It is the sprocket that drives the chainsaw chain. All parts of this mechanism are closely interconnected; failure of the headset leads to disruption of the instrument.
Causes of malfunctions and how to determine the need for replacement
When idling, the spring compresses the cams and they do not touch the drum. As the speed increases, the centrifugal force exceeds the spring stiffness and the cams come into contact with the walls of the drum. The latter begins to rotate.
The teeth of the saw chain mesh with the teeth of the drive sprocket. One of the functions of an automatic centrifugal clutch is to protect the engine when the load on the chain increases beyond the permissible limit. This can occur when the chain gets stuck.
The outer part of the drum is covered by an emergency brake band. When the handle is folded back, the belt is pressed against the drum and slows down its rotation. The effect is the same as when the chain jams.
A feature of all chainsaws is that the drum and clutch cams are attached to the shaft using a nut with a left-hand thread so that the mechanism does not unwind during operation.
Wear on the drive sprocket teeth can occur for several reasons:
- natural wear and tear along the chain teeth;
- accelerated wear as a result of excessive chain tension or lack of lubrication;
- incorrectly selected chain;
- technological defect.
Metal wear can be determined visually by inspecting the sprocket without removing it from the saw. Dents and chips on the surface should not exceed 0.5 mm.
The need for replacement is determined by increased noise when the chain moves, but this is typical only in the presence of deep potholes. It is difficult to notice shallow wear during operation, but the chain will wear out greatly. When the teeth are broken, the chain may move jerkily, which is especially noticeable during operation.
The clutch operates automatically, depending on the number of engine revolutions.
The units are equipped with a centrifugal clutch, which operates automatically, depending on the number of engine revolutions.
When the engine of the unit operates at idle or low speed, the elements of the clutch basket, which have friction linings, have a certain level of freedom in the circular direction. The presence of freedom of movement leads to the fact that, under the action of springs, the elements are attracted to the center of the rotation shaft and do not transmit rotational motion to the sprocket drum.
As the engine speed of the device increases, the centrifugal force exceeds the force of the springs, which leads to displacement of parts with friction linings. Replacing the piston on a Chinese chainsaw. Replacing the piston group of a Chinese chainsaw 4500replacement piston group of chainsaw 4500 cylinder-piston group for a 45 mm chainsaw replacing the piston group on a chainsaw stihl ms180 chainsaw china replacement.
Replacing the sprocket on how to unscrew the clutch on a chainsaw. On a Chinese chainsaw. These elements are pressed against the inner walls of the drum under the influence of centrifugal force. Due to this contact, rotational motion is transmitted to the drum and sprocket, which drives the saw chain of the tool.
More common reasons that force tool repairs associated with replacing the drive sprocket are:
- chain jamming due to defects appearing during operation of the unit;
- the highest wear of the sprocket as a result of long-term operation of the unit.
- professional;
- household.
The main difference between them is the frequency of replacement and the rate of wear: in the models of the “Pro” series, wear occurs faster and repairs occur more often.
The latter consist of a hub with a stationary crown of a certain number of teeth. Their factory pressing does not allow the crown to be removed separately from the hub. This situation is typical for many Chinese chainsaws, for example, from the Champion brand.
The situation with prefabricated sprockets is simpler: the removable crown is quickly unscrewed from the drum axis, so repairs do not cause any particular difficulties. This option is an advantage of most saws of European origin, for example, Shtil or Husqvarna.
Drive gears, according to their design, are divided into:
- Whole. The part includes a hub into which the crown is pressed. You can only remove the part for replacement in its entirety. In the industrial conditions of the manufacturing plant, it is possible to ensure the design values of the interference. Special equipment is used for this. This operation cannot be carried out in a home workshop. Difficulties also arise when trying to buy a crown separately - the manufacturer does not consider it an independent part and does not supply it to stores and service centers.
- Prefabricated. The crown is made as a separate part; it can be removed using a special puller or special tricks with a universal tool.
Solid sprocket
Experts identify the following signs of wear on the drive gear teeth:
- semicircular depressions are visible at the base of the tooth;
- the thickness of the tooth varies with height;
- chipped zones at the top;
- scratches appeared inside the hub hole;
- the chain has worn out the groove on the sprocket;
- When starting, the chainsaw jams.
A chainsaw sprocket with such signs should not be used; it must be removed and replaced.
According to the manufacturer's recommendations, the tool should be inspected before starting work. In this case, be sure to check the condition of the saw bar and whether it is securely fastened. If the screw that regulates the position of the chain roller and its tension is loosened, or the nuts securing the bar to the body are loosened, it deviates from the plane of the chain.
Sprockets with replaceable and stationary crown
After tightening the fasteners and making adjustments, do a test run. If free play remains, the sprocket will have to be removed and replaced.
The Husqvarna 137 chainsaw is an amateur, semi-professional class tool. The model achieved high popularity among consumers due to its good performance, light weight and versatility. These days, the Husqvarna 137 chainsaw is actively used not only by gardeners, but also by utility workers.
There are already several 10-cylinder chainsaws in operation from different manufacturers, capacities, and most importantly for special purposes. Saws are divided into:
- prof (for felling and construction);
- household (garden).
Currently reading: How to Adjust the Ignition on a Chainsaw Partner
Accordingly, their drive gear will be different, as well as the sequence of actions. Discover 253 best selection of husqvarna chainsaw sprockets 142 chainsaw chainsaw replacement. Assembling a husqvarna 142 chainsaw. Husqvarna 140 chainsaw. Replacing a chainsaw sprocket. Husqvarna 340 chainsaw repair, chainsaw replacement sprocket.
In this regard, you need to know how to remove the sprocket from the chainsaw correctly so as not to damage the tool. This part is also called a centrifugal mechanism or clutch disc.
To better understand the entire process, it is necessary to understand what an asterisk is and how it is used.
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If the part is not replaced in a timely manner, the stability of the tool will be impaired. A worn part provokes excessive vibrations, which, in turn, have a negative effect on the crankshaft bearings.
Tooth wear of up to 0.5 mm is considered normal. However, users often bring the part to a deeper groove of about 1 mm, not realizing that operation causes damage to other parts of the chainsaw. Naturally, subsequently there is a breakdown of the bearings, which need to be replaced.
When the engine of the unit is running at idle or low speed, the elements of the clutch basket, which have friction linings, have a certain level of freedom in the radial direction. The presence of freedom of movement leads to the fact that, under the action of springs, the elements are attracted to the center of the rotation shaft and do not transmit rotational motion to the sprocket drum.
When the engine speed of the device increases, the centrifugal force exceeds the force of the springs, which leads to displacement of elements with friction linings. These elements are pressed against the inner walls of the drum under the action of centrifugal force. Due to this contact, rotational motion is transmitted to the drum and sprocket, which drives the saw chain of the tool.
The main advantage of this type of clutch is that when the saw chain jams, elements with friction linings slip, which protects the internal combustion engine from serious damage.
The main malfunctions of chainsaws and steps to eliminate them are described here.
Features of the Husqvarna 137 chainsaw, which is suitable for all types of work in gardens and households, plantations, small factories and more, is designed with a 2.2 horsepower engine. The fuel tank is designed for 0.4 liters. Recommended tire for Husqvarna 137 chainsaw.
H30, and the length can vary from thirty-four to thirty-eight centimeters. It should be borne in mind that in order to avoid early wear and unforeseen failures, you can not only meet the manufacturer's performance requirements, but also use original spare parts for the Husqvarna 137 chainsaw, which are in an affordable price range.
Types of stars
Depending on the class of chainsaw, all sprockets are divided into two groups - professional and household. The first type of parts have increased wear resistance and are made of durable metal alloys that are not subject to corrosion and mechanical damage. Household ones more often require replacement and scheduled repairs; if the tool is actively used, diagnostics are recommended every six months. Based on their design features, the following types of sprockets can be distinguished:
- Prefabricated . The removable crown can be easily unscrewed from the drum axis, which simplifies checking and replacing this part. Almost all European chainsaw models are equipped with such stars.
- Solid . They consist of a hub and a stationary crown (the number of teeth may vary; you must carefully read the instructions for the chainsaw). Due to the factory press fit, the ring cannot be removed separately from the hub, so in the event of a breakdown it is necessary to disassemble the entire clutch drum. This mechanism is usually found on Chinese models.
If you plan to service the chainsaw yourself, it is recommended to purchase a tool with a professional type of drive sprocket. It should be collapsible, which reduces the cost of repair and maintenance of the instrument.
Sequencing
Chainsaw sprocket, ring and bearing
The vast majority of household saws are sold under the Partner brand. It is enough to simply change the sprocket in them, even at home, by purchasing a repair kit.
Since most often the sprocket in household saws is a assembled mechanism, it rotates due to the bearing. That is, when changing the sprocket, you inevitably change the bearing and the shaft.
In professional models (such as Shtil and Husqvarna), as well as in household ones, if it is not possible to have a specialized wrench on hand for removing the star, they use a soft cord with a diameter of 5-6 mm.
In all cases, the sequence of actions is as follows:
- The side cover must be opened to gain access to the tire and sprocket.
- Next, you need to remove the tire by loosening the chain.
This is what a chainsaw tire looks like
- Once the sprocket is free, you need to unscrew the spark plug to gain access to the engine piston.
When is replacement necessary?
The saw set and drive sprocket are subject to natural wear and tear during operation. This is not a breakdown, but a planned tool maintenance procedure. Reasons for replacing the sprocket:
- intensive and prolonged use of the saw;
- mechanical shocks of the headset;
- Using an unsuitable chain.
Figure 2 – Chainsaw chainsaw chainsaw
Normal wear on the teeth of the drive sprocket is up to 0.5 mm. With regular use, this figure can reach up to 1 mm, but over time this will lead to a load on the engine and damage to other parts of the saw. The need for replacement or repair can be determined by the following signs:
- there is mechanical damage on the guide sprocket;
- the width of the teeth is disproportionate to their height;
- there are asymmetrical angles;
- There are chips, grooves or large burrs on the hub.
How much does a sprocket and its replacement cost?
The price of a chainsaw sprocket is highly dependent on the manufacturer and is somewhat lower than the cost of the saw chain. To avoid regular replacement, manufacturers recommend operating the saw with several chains and periodically swapping them. In this case, the wear of the sprocket teeth occurs more evenly.
The cost of replacement in service centers is commensurate with the price of the part itself, so it makes sense to do this work yourself, especially since no adjustments need to be made after this.
How to change a star on a chainsaw?
If the chain begins to vibrate even at low speeds, the chainsaw can be used for a long time without replacing parts - it is required
carry out diagnostics and, if necessary, change the components of the saw set. For a planned replacement, you will need a new clutch drum or wheel, depending on the specific model, and a basic set of tools:
- spark plug key;
- cable up to 15 cm long or piston stopper;
- factory key for removing the coupling;
- adjustable wrench or wrench.
Figure 3 - Necessary tools for replacing the star
It is recommended to have a round file, pliers, a vice and a knife to eliminate defects in the design of the chain set (if only tooth correction is required).
How to unscrew?
It is easy to remove and replace this part yourself. Working technology:
- Attach the piston to the saw cylinder. To begin, remove the protective cover on the housing, the air filter and unscrew the spark plug. Install a special piston stopper into the hole formed; instead, you can use a thick nylon cord or wire up to 15 cm long. If the piston is in the way, you can slightly turn the sprocket or move the chain clockwise.
- Unscrew the bolts on the cover that secures the tire, remove the protective casing. Loosen the chain tension or remove the saw attachment. At the same time, you can clean it from dust, dirt and sawdust.
- Depending on the model, the sprocket acts as an element of the clutch drum or is built in separately. In the second option, remove this part and replace it with a new one. The one-piece design is difficult to repair - the unit must be disassembled. To do this, unscrew the coupling clockwise and remove the drum. Check structural parts for wear and deformation.
Figure 4 – Replacing the star with a new one
If the sprocket is an element of the clutch drum, then the entire part will have to be replaced. When replacing, you should pay attention to the suitability of the model - it must be similar to the factory one.
How to assemble?
Assembly of the coupling mechanism should be carried out in the reverse order. First install the sprocket on the needle bearing, then put on the drum, washer, gasket and the clutch itself. Tighten counterclockwise and secure the piston with a slight movement.
If the chainsaw has an oil drive spring, it may be built into the drive sprocket. In most models, the correct location of this element is marked with a special color or notch. To get to the desired position, turn the sprocket until it clicks.
The last stage of assembly is installing the saw bar. During this process, you need to release the handbrake and then check that the chain teeth are in the correct slots. After installation, mount the chainsaw chain to working condition. Finally, remove the stopper, screw in the spark plug and replace the filter. The final repair step is to secure the protective housing cover.
Important ! When removing a chainsaw sprocket, clutch or clutch drum, it is recommended to take the part with you to the store. This will allow you to choose a suitable analogue.
Chainsaw sprocket and its functions
Before you figure out how to change a sprocket on a chainsaw, it’s worth understanding what sprockets look like and the problems associated with them. Sprockets have star-shaped teeth that guide the chain to the outside of the sprocket for smooth operation. Ring sprockets: Ring sprockets have a rim that moves freely around a spline to guide the chain around a pin with internal teeth.
Drive sprocket. This is a very important and often overlooked part of chainsaw maintenance. Drive sprockets are selected according to the length of chain you are using. They should be changed every 2 - 3 times the chain is replaced. Try to determine which rim or sprocket you have. Installing a rim and sprocket means it is easier and cheaper to change the rim, which is the part that drives the chain. They wear out faster, but they are cheaper. The rim must be replaced if it is worn by 0.2 mm.
Changing the rim on Stihl chains is easy. On chainsaws where the rim is inside the clutch, such as some Husqvarnas chainsaws, you must remove the clutch first.
Sprockets drive the chain directly from star-shaped teeth on the sprocket itself. When they are worn, the entire sprocket must be replaced. They tend to wear out more slowly, but cost more when you replace them.
The side sprockets and rear clutch sprockets are easy to change. Removing the built-in sprockets is more difficult because the clutch assembly must be removed first. This requires you to remove the spark plug and use a tool to stop the piston.
If you continue to use a worn sprocket, it will begin to damage the drive links, which in turn widens the groove, which then produces poor cutting, which further accelerates wear on all parts! This is a particularly serious problem for longer rods.
Sometimes the bearing on the sprocket needs to be replaced. It's a simple case of removing the sprocket, sliding out the existing bearing and replacing it with a new one.
Features of replacing a star for chainsaws of different brands
When replacing or repairing a chainsaw, you should take into account the design features of the model. Specifics of servicing coupling drums from popular manufacturers:
- Stihl (Calm) . Models of this brand have one-piece and collapsible types of sprockets. To unwind the clutch you will need a 19mm socket and a wrench. Please note that the thread is left-handed, and a reflective plate is installed behind the clutch (a consumable material that often breaks when diagnosing the drum).
- Partner (Partner) . The peculiarity of this brand is that when replacing a sprocket, it is recommended to change the bearing as well. If you ignore this step, after scheduled repairs there is a risk of disruption of the chain and a change in the pitch during active sawing.
- Husqvarna (Husqvarna) . Many Husqvarna models use a sprocket with a replaceable ring. This simplifies routine replacement and repairs. When disassembling the tool, you will need a 13mm wrench to fix the shaft from the impeller side.
- Carver (Carver ). Unlike other manufacturers, there are no specific clutch design features. Depending on the brand, the star can be solid or collapsible.
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.
How to reduce drive sprocket wear?
The service life of a chainsaw clutch can be increased by routine maintenance and high-quality maintenance of the tool. Helpful Tips:
- Apply grease to the needle bearing after each sprocket replacement;
- correctly select all parts of the saw set depending on the chain pitch, use reliable consumables;
- do not replace parts of the clutch and saw at the same time - this leads to a change in pitch and wear of the headset;
- Clean the saw regularly by removing the side guard.
During operation, you should carefully monitor the sound and behavior of the circuit. If it begins to jam, vibration and rattling appear - diagnostics are required.
Replacing the sprocket in a chainsaw is a planned procedure that ensures reliable and stable operation of the tool. When diagnosing or repairing the coupling mechanism, the design features of the model and the manufacturer’s requirements should be taken into account. To avoid frequent breakdowns, it is recommended to use only original parts or high-quality analogues, and systematically clean the chainsaw.
Design problems of different models
The problem is complicated by the design of branded chainsaws, which requires replacement of a worn drive only after complete dismantling of the clutch mechanism and other components. In another option, in order to remove the sprocket from the chainsaw you need to have a special key.
A design feature of a significant part of chainsaw imports is the placement of a sprocket on the clutch mechanism.
- If the teeth are significantly worn, the drum, which is integral with the drive, must be replaced.
- A more advanced design of the drive sprocket allows you to restore the performance of the part by replacing the ring.
In the list of factory kits supplied with saws, such a tool is extremely rare. The problem is solved by replacing the worn-out part in a service workshop or by making the necessary device at home.
Algorithm for self-replacement of the clutch drum with sprocket
Removing the chain
As with any other tool, chainsaws require careful maintenance. It is necessary to constantly check the oil supply to the chain, chain tension, operation of the brake, ignition system, etc. Fortunately, almost any problem can be solved at home on your own.
- dismantling the headset and air filter;
- installing a piston retainer in the spark plug hole;
- The clutch and the gear drive, integral with the drum, are removed using a puller; the sprocket can only be unscrewed clockwise.
If significant wear of the separator, breakage of the springs of the centrifugal mechanism and cams are detected, it is recommended to replace the entire set.
If the condition of the removed parts is beyond doubt, the entire mechanism is assembled in the reverse order. To securely fix the clutch on the crankshaft, it is enough to unscrew the piston stopper, pull out the standard starter cord and return it to its original position.
Amateur craftsmen should be warned against simplifying the requirements of repair technology and saving money by installing relatively cheap Chinese components.
The quality of the work done is guaranteed by attention, accuracy, and compliance with the sequence of all dismantling and assembly operations.
Alternative solutions
The sequence of operating moments is identical for almost all known models on the domestic market of chainsaw equipment. Experts advise using a branded part for replacement.
If we are talking about modernizing this unit, the feasibility of such a change should be clarified by consulting an experienced specialist.
The best option is to purchase a repair kit, which also includes a replacement bearing. In addition to the key, you may need a clutch drum puller individual for each model, a metal or plastic stopper to fix the piston in a given position.
