The movement of the chain on the tire chainsaw is due to the drive sprocket connected to the engine gearbox.
Wear on the sprocket on the sprocket means that it needs to be replaced as soon as possible, otherwise it will not clutch with the chain and the chain itself will be damaged.
In this case, it must be taken into account that the drive sprocket has a number of features depending on the model of the saw and its type. In this article, we will highlight such a question as how to remove an asterisk from a chainsaw.
Feature of saw designs
Professional chainsaw brand STIHL
In operation, there are already several dozen chainsaws from different manufacturers, capacities, and most importantly special purposes. The saws are divided into:
- professional (for felling and construction);
- household (garden).
Accordingly, the drive gear will be different for them, as well as the sequence of actions. This is a feature of saw gearboxes. With most professional tools, the tire can change its location on the saw in two planes.
The main malfunctions of chainsaws and actions to eliminate them are described here.
Chain sprocket, crown and bearing
The vast majority of household saws are sold under the brand name Partner. They simply change the star even at home, having bought a repair kit.
Since most often the asterisk in household saws is a prefabricated mechanism, it rotates due to the bearing. That is, changing the sprocket, you inevitably change the bearing and not the shaft.
In professional models (such as Stihl and Husqvarna), as well as in household ones, if it is not possible to have a specialized key for removing a star, use a soft cord with a diameter of 5-6 mm.
In all cases, the sequence of actions is as follows:
- You must open the side cover to gain access to the tire and sprocket.
- Next, remove the tire by loosening the chain.
It looks like a chainsaw tire
- After the sprocket is free, you need to unscrew the spark plug to access the engine piston.
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- Manually rotating the sprocket, bring the piston almost to the very top of the channel and fill the hole most tightly formed from the candle with a soft cord, thereby blocking the movement of the piston.
- Use the open-end wrench and unscrew the sprocket, depending on the model of the saw and the type of gearbox.
Thus, adhering to the recommendations given in the article, you can easily remove the sprocket from the chainsaw yourself.
How to remove and replace the drive sprocket on Husqvarna and Stihl chainsaws is described in detail in this video:
How to remove an asterisk from a chainsaw: varieties and design features
With the constant use of such a tool as a chainsaw, it is important to regularly carry out diagnostic measures, replacing consumables and parts. One such consumable is an asterisk or chain drive mechanism. If the question arises of how to remove the sprocket correctly from the chainsaw, then the time has come to replace it. When and how to correctly replace crowns on chainsaws, we will consider further.
What is the chainsaw sprocket for?
Chainsaw sprockets are clutch basket parts designed to rotate the chain. On chainsaws, a centrifugal drive type is used, the operation of which is automatic, which depends on the speed of the engine itself.
The device of the centrifugal mechanism is such that when the chainsaw is idling, the sprocket does not rotate. This is because the elements of the clutch basket have a degree of freedom. This freedom is ensured by friction pads and springs. As the number of revolutions increases, the centrifugal force increases the force of the springs, as a result of which the elements with friction pads are displaced. In this case, torque is transmitted to the drum and sprocket, which, in turn, moves the saw chain.
This design of the clutch mechanism is due to the fact that when the chain is jammed, it slips. Thus, it is possible to prevent jamming of the internal combustion engine, as well as to avoid its premature failure. Regular use of the saw causes the crown to wear out, and there is a need to replace it.
The leading sprocket of a chainsaw can be of two types: combined or solid (stationary). One-piece has the form of a monolithic device, which is located directly behind the clutch. Such asterisks in the form of a clutch plate with a welded gear star are also called stationary. This type of design is used in most chainsaws. Replacing such crowns on a chainsaw does not present any difficulties, but it will only be necessary to remove them entirely with a drum.
Video: How to Change the Sprocket on a Partner Saw
On expensive chainsaws, prefabricated sprockets are used. The crown is put on the drum shaft, resulting in the transmission of torque to the chain. Replacing a prefabricated device is even easier, since the crown is removed, while the drum remains in place. The prefabricated structure of the element under consideration is a way to extend the life of the clutch. After wear on the drive sprocket, replacement is required. If this is not done, then the tool life is significantly reduced, resulting in an increase in the rate of wear of the internal combustion engine.
How to determine the need for crown replacement
The sprocket is replaced immediately after the product in question wears out and cannot fulfill its functions. The wear of the crown can be determined by the following characteristic properties:
- The presence of noticeable radii in the area of transition of the tooth to the cavity.
- Chipped metal on top of teeth.
- Uneven tooth width.
- Detection of scoring on the inside of the hub.
- Grooving from the tire.
- The chain is off the tire.
The most important sign by which to check on the above items is the occurrence of signs of jamming of the chain when starting the chainsaw. Any of the above factors requires immediate replacement of the item in question. Details on the types of leading stars and their differences can be seen in the video.
How to remove an asterisk on a chainsaw
Before changing an asterisk on a chainsaw, you must first purchase a new element. The drive sprocket should be changed based on what type of element is used on the chainsaw. One-piece devices are often used on domestic and semi-professional ones, and prefabricated ones on professional units.
The process of removing an entire product is the following:
- Initially, the casing is dismantled.
- After that, the saw bar is removed together with the chain.
- The snap ring and washer are removed.
- After that, you can remove the clutch together with the drum.
- The crown from the drum is removed using a special key, which is usually attached to the instrument.
After replacement, reassemble the removed parts in the reverse order. The process of replacing the crowns of the prefabricated type is almost similar to dismantling the whole product, only, ultimately, you should only change the gear element without a drum. After the work done, you need to check, evaluating the effectiveness of the actions taken. To do this, chain is tensioned using the tensioner adjusting screw.
It’s important to know! Stationary crowns can be replaced with prefabricated ones, which will save significantly.
From the above it follows that the replacement of crowns is an important diagnostic measure, if not observed, the owner of the chainsaw risks premature occurrence of the need for major repairs of the motor. The video above shows excellent material that describes all the details of the design, removal and replacement of the chain saw sprocket.
Replacing the drive sprocket on a chainsaw
Regardless of the class of the chainsaw and its operational characteristics, the design of removable saw sets is almost identical. The saw device kit includes a guide bar made of a special alloy and a chain, which is activated by the gear ring of the drive mechanism. To extend the life of the saw chain, timely replacement of the sprocket on the chainsaw is important.
The feasibility of timely replacement of worn parts of the drive chain
The design of its crown determines such an important parameter as the choice of chain by step.
- Installing a new part on a worn sprocket reduces its smoothness, accelerates wear, and initiates the risks of breakage and the creation of a traumatic situation.
- There is also an increase in operational loads on the engine and the elements of the kinematics of the tool.
- A similar process takes place when old extended chains are installed on the tire, the diameter of which is adjusted to the size of the tire by removing part of the links.
Experts also do not recommend arbitrarily changing the size of the stars. An experiment can adversely affect the engine resource and the kinematics of the instrument as a whole.
Safety of sawing operations of various degrees of complexity is ensured by the effective operation of the emergency stop brake and devices that block the expansion of the chain ends in case of an accidental break. In any case. the most reliable prevention of contingencies, maintaining the chainsaw in good condition.
A way to extend the leading sprocket resource
In practice, for uniform wear of the crown of the sprocket, a set of several chains of the same type is used, which alternately change as the cutting edges of the saw links become blunt. However, sooner or later, the user is faced with the need to replace a worn part.
Criteria for choosing a repair kit yourself
The desire of the owner to equip the headset with a saw chain with another step, leads to the need to change the asterisk to a part with a crown of the corresponding profile. This requirement applies to the entire range of European and Chinese chainsaws.
The operational reliability of a European-assembled saw, when operating in difficult conditions of increased loads, can significantly deteriorate if, instead of the original part, a Chinese asterisk is used.
Structural problems of different models
The problem is complicated by the design of branded chainsaws, which provides for the replacement of a worn drive only after the complete dismantling of the clutch mechanism and other components. In another embodiment, in order to remove the sprocket from the chainsaw, you must have a special key.
A design feature of a significant part of chainsaw imports is the placement of an asterisk on the clutch mechanism.
- With significant wear of the teeth, the drum is to be replaced, which is a single unit with the drive.
- The more progressive design of the drive sprocket allows you to restore the performance of the part by replacing the crown.
In the list of factory kits attached to the saws, such a tool is extremely rare. The problem is solved by replacing the parts that have exhausted the resource in the service workshop or by making the necessary fixtures at home.
The lack of prerequisites for the restoration of a worn star
The leading sprocket for a chainsaw of any power category is made of special steel, processed by a special technology, so repairing a part by welding by arc welding and subsequent milling is not possible.
The price of the part itself is several times lower than the cost of replacing it in service structures.
- The benefits of self-repairing a drive unit at a lower cost and time.
- If you have the appropriate tool, you can manage the work for a fairly short time interval.
The sequence of working moments is identical for almost all known models in the domestic market of chainsaw equipment. Experts advise using a branded part for replacement.
If we are talking about the modernization of this node, the feasibility of such a change should be clarified by consultation with an experienced specialist.
The best option is to buy a repair kit, which also includes a replacement bearing. In addition to the key, you may need an individual for each model puller of the clutch drum, a metal or plastic stopper to fix the piston in a predetermined position.
Algorithm for self-changing drum clutch with sprocket
Leading sprocket replacement technology provides for the implementation of the entire amount of work in a given sequence:
- dismantling the headset and air filter;
- installation of a piston retainer in the spark plug hole;
- the clutch and the gear drive made at the same time as the drum are removed by means of a puller; the sprocket can only be unscrewed clockwise.
If there is a lot of wear on the separator, breakdown of the springs of the centrifugal mechanism and cams, it is recommended to replace the entire kit.
If the condition of the removed parts is not in doubt, the whole mechanism is assembled in the reverse order. For reliable fixation of the clutch on the crankshaft, it is enough to unscrew the piston stopper, pull out the cord of the standard starter and return it to its original position.
It should be cautioned by amateur craftsmen from simplifying the requirements of repair technology and saving money on installing relatively cheap Chinese components.
The quality of the work done is guaranteed by attention, accuracy, compliance with the sequence of all dismantling and assembly operations.