How to change a chain saw drive sprocket
chain saw drive sprocket. why change it??
In order to transmit the rotational force created by the power unit to the regular cutting headset, the design of any modern gasoline-powered saw includes a clutch. Its stability is ensured by the drive sprocket, the good condition of which determines the speed of the cutting assembly. Sprocket is in constant contact with the drum during operation. Over time, it will wear out and break, causing the entire garden chain saw to lock up. To solve the problem, you need to learn the rules for replacing a chainsaw drive sprocket.
Untimely replacement of the sprocket on a chainsaw can result in several serious failures, the elimination of which will cost the gardener much more than the installation of a new clutch element.
These faults include:
- Accelerated wear and a reduction in the original smoothness of the chain. this is especially common for gardeners who install new chains on chainsaws with worn old drive sprockets;
- a sudden increase in stress on the engine cylinder head, increasing the risk of burr formation on the cylinder surface and distortion of the piston;
- accelerated wear of the reel and breakage of the clutch spring.
Another problem caused by not replacing the drive sprocket on time is the creation of an injury-prone situation. A chainsaw with a worn sprocket can cause an instant cut or other injury to the cutting assembly, which can lead not only to cuts in the chain but also to other people around the saw.
Drive sprocket replacement on a chainsaw
A chainsaw is designed as a classic mechanism that is powered by an internal combustion engine. The construction of the tool is designed to use the simplest single-cylinder, two-stroke carburetor gasoline-based engine. Because of the simplicity of these engines and the design features of the gasoline chainsaw, this unit is a reliable and dependable piece of equipment that can withstand harsh operating conditions.
The chainsaw does not require any special knowledge or skill to operate. The only way to be sure you get long, trouble-free use of your machine is to have it inspected and serviced at regular intervals. You should replace worn parts when using the appliance at regular intervals. To reduce wear on the appliance, keep the chain and drive sprocket well lubricated and check the chain and drive sprocket for signs of wear.
Before a chainsaw is repaired, it is important to understand the design of the chainsaw. To replace a major structural element, such as the drive sprocket, you need to familiarize yourself with the mechanism of interaction between the clutches on the machine.
How to replace chainsaw drive sprocket/rim sprocket Husqvarna 359
The design of a chainsaw drive sprocket
The sprocket or centrifugal mechanism is a part that resembles a star. It absorbs the motor’s torque and transmits it to the guide bar and saw chain. It guarantees the rotation of the cutting attachment and the sawing process. It is triggered in automatic mode, which depends on the value of the engine speed. The clutch drum can be located both outside the chainsaw and inside it. under a separate cover. It has a protective function not only for the material from which the sprocket is made, but also for the operator, who could be injured by it during operation. In addition to its function of rotating the chain, the drive sprocket prevents the motor system from malfunctioning if the chain jams or stops turning.
Why the drive sprocket needs to be replaced
Among the most common reasons, as a result of which the tool may need to be repaired, is the replacement of the drive sprocket. The part becomes unusable because of:
- The chain jams if any defect occurs during the use of the equipment;
- High sprocket wear from prolonged use of the chainsaw.
Regular use of the tool contributes to increased wear of the part due to the impact of increased load when sawing wooden materials. Several ways of using the tool are known:
In the first way of using the tool, the operation of the saw occurs until it is completely worn out. This method has certain disadvantages, among which is the problem of carrying out manipulations to control wear as a result of intensive use.
If you work with two or more chains, you can get even wear on each chain and sprocket, which will greatly extend the life of the machine and reduce the need for frequent drum changes. It is also important to keep in mind the condition of the bearing in the drum. Operation of this structural element occurs at any engine revolution. When replacing the sprocket, it is also important to take care of replacing the bearing and clutch.
Untimely repair contributes to increased vibration, which affects the increase in wear indicators of parts that are installed in the engine of the device on the crankshaft half. The depth limit for sprocket teeth wear should not be more than 0.5 mm. Sprockets have twice the service life of chains. For this reason it is recommended to use two chains.
When the service life of each chain is exhausted, it is necessary to replace the chain and the drive sprocket at the same time.
Main sprocket replacement on Husqvarna 154, 254, 262 chain saws
For the models of Husqvarna 154-series, 254-series, 262-series chain saws
, equipped with a 0.325 pitch 8-tooth chain, the Rezer SP 38071 drive sprocket is used. This part differs from the previous one in its metal construction. That means there is no such thing as a replacement ring.
On the one hand, this part loses
in service life. the other has a more attractive price. Price is half as much as for a sprocket with a replacement ring. To purchase sprockets for Juxtaphone 154, 254, 262 models, click on the following link.
How to change a sprocket for Husqvarna 154, 254, 262
has a slightly different algorithm. Let’s look at it in detail.
Remove the chainsaw sidewall to gain access to the saw group
With a combination wrench
Loosen the chain and remove it together with the stitching.
Remove the cable starter
on the opposite side. Use Allen wrenches.
Use a 13 mm open-end wrench to fix the shaft at the impeller side
Using a special key
Remove the clutch clutch. Unscrewing must be clockwise.
Reassemble in reverse order
The clutch clutch should be tightened counterclockwise. the force must not be too high. because the clutch is self-tightening in rotation.
In essence, the replacement process is not very complicated
and it is possible to do it yourself. Buy quality sprockets for Husqvarna 154, 254, 262 in our store TUKINGARDEN.
Top Reasons to Replace a Drive Sprocket
A universal spanner is the basic tool for changing a sprocket.
The most common reasons for tool repairs involving replacement of the drive sprocket are
- the chain jams due to faults in the chain during operation of the machine;
- High sprocket wear caused by too much use of the machine.
If the device is used regularly, it causes increased wear of the drive sprocket as a result of the increased loads it is subjected to when sawing wood. There are two ways of operating the unit:
In the first method of operation, the chain is operated until it is completely worn out. This method has several disadvantages. The main one is the problem of checking the wear during heavy use of the machine.
If two or more chains are used in the process, it is possible to achieve uniform wear of the chain and sprocket, thus prolonging the operation period of the unit until a repair consisting of replacing the sprocket is made. In addition to sprocket wear, the bearing in the sprocket should not be forgotten. This design element operates at all engine speeds. If the sprocket is replaced, the bearing must also be replaced at the same time.
The clutch, complete with sprocket, must be replaced in a timely manner. If repair work is not performed in time during operation, the tool experiences increased vibration that leads to increased wear of the bearings installed in the internal combustion engine on the crankshaft halves. Max. wear depth of the sprocket teeth should not exceed 0.5 mm. Sprocket life is twice as long as one chain, so two chains should be used. When the chains are nearing the end of their useful life, they should be replaced with sprockets and drive sprockets at the same time.
Design Features of Drive Sprockets
Pinion tooth pitch is one of the main parameters of the assembly. It must match the pitch of the chain links and, last but not least, the tooth pitch of the sprocket at the end of the chainwheel bar.
Drive sprockets are subdivided according to their design features:
- Whole. The part includes a hub that has a pressed ring gear. Part can only be removed as a complete unit for replacement. Design interference values can be achieved in the factory at the manufacturer’s facility. Special tools are used for this. This cannot be done in a home workshop. Difficulties also arise when trying to buy a crown block separately Manufacturer does not consider it an independent part and does not deliver it to stores and service centers.
- Assembled. The ring gear is made as a separate part, it can be removed with a special puller or special tricks with a universal tool.
Specialists distinguish the following signs of drive pinion tooth wear:
- there are noticeable semicircular depressions at the base of the tooth;
- the thickness of the tooth varies with the height;
- chipped areas on top;
- there are scratches inside the hub hole;
- the chain rubbed the groove on the sprocket;
- the chain saw jams when starting.
The chain saw sprocket with such signs should not be operated, it should be removed and replaced.
According to the manufacturer’s recommendations, the tool should be inspected before starting work. The condition of the bar must be checked to see if it is securely fastened. If the screw that regulates the position of the chain roller and its tension is loose, or the nuts that fasten the bar to the housing it deviates from the plane of the chain. In this case the rollers of the blade rest not in the middle, but on the edges of the teeth, increasing the load on them and on the chainsaw as a whole. Increased wear leads to premature failure.
Sprockets with changeable and fixed sprocket head
After tightening the fasteners and adjustments do a test run. If there is any play left, the sprocket will have to be removed and replaced.
Features of the clutch drum in chainsaws
The drum, located in the carrier of the mechanism, is an integral part of the chain drive system. This part has a star shape that resembles a sprocket, that’s why it got its nickname. Depending on the chainsaw, it can be a professional or a home appliance. Because chainsaws are used more often than domestic saws, the drive sprocket needs to be replaced regularly. If we talk about household tools, then there is everything depends on the amount of work performed and the load placed on the chain device.
Sprocket, ring and saw bearing need replacement in most cases.
In any case, the main reason for changing the sprocket is the chain wear of its teeth. In this case, when the unit has a solid drum, the chain surface cuts through it almost completely, which requires a complete replacement of the entire part. If the chainsaw has a drum with a removable sprocket, it can be limited to replacing the sprocket.
Chainsaw Repair. Replacing the Drum and Sprocket (Poulan Part # 545171901)
Usually, in order to remove the chain saw sprocket, many people turn to special service centers, but if there is a need to save the home budget, you can do this work without the help of others. This activity does not look complicated, but you must have all the necessary parts and tools. The process of changing the sprocket is the same for any model.
How to change the gas chainsaw clutch and drive sprocket
How the chainsaw’s automatic centrifugal clutch works.
Most brand-name, quality chainsaws have a centrifugal clutch from the start. It is distinguished by high reliability, increased service life and works in the automatic mode, that is, independently triggers when the power unit reaches the necessary speed of rotation. The factory centrifugal mechanism consists of durable friction plates, a chainsaw clutch drum and steel return springs. The friction plates of the mechanism are capable of radial movement. They are pulled up against the crankshaft by the springs when the engine is running at low speed.
At the same time, the built-in metal drum, which is initially connected to the cutter chain sprocket, is set in motion. If the engine reaches a high enough speed, the force of the built-in springs is reduced in relation to the centrifugal force created. This causes the springs to press against the inside surface of the drum and actuate it.
The centrifugal clutch principle has an important advantage. it automatically slips when the cutting chain jams. That prevents the power unit from shutting down and keeps on going.
To avoid unplanned repairs the chain saw operator should follow certain recommendations. They will help to extend the life of your chainsaw clutch and protect it from damage to the chain saw’s main active components.
- regularly lubricate the clutch parts;
- Timely cleaning of the mechanism from dust and dried oil;
- operate your chainsaw only with a fully serviceable guide bar and a well-sharpened chain;
- Avoiding hard metal objects from striking the mounted cutting attachment.
Chainsaw clutch wear is caused by a faulty brake lever. To avoid further breakage, the operator must constantly check the lever and not allow the chain to rotate while the inertia brake is engaged.
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 produces the saw.
Its main structural elements are:
The operating principle is as follows. When the saw starts up, the components that can move freely in a radial direction are compressed against the axis of the shaft. In this case, no torque is applied to the drum and hence to the sprocket and guide rail. The moment the centrifugal force exceeds the force potential of the springs, the clutch elements loosen and compress at the inner drum causing the drum to torsion. Together with it the rotary cycle is transferred to the sprocket and the chain-and-slat bar itself.
The main advantage of this type of clutch is that it slips when the cutting part is suddenly braked, which does not stop the engine. The result is that the heart of the saw. the motors. remain in one piece.
When chain saw is idling the clutch weights, though they rotate together with the crankshaft, do not touch the clutch drum (also known as clutch cup), because they are compressed by the spring and therefore do not transmit torque from the engine to the saw unit. When the engine speed reaches 4000 rpm, the clutch weights under the influence of centrifugal force unclenching and resting their own outer friction surface on the inner surface of the clutch drum, begin to rotate it, thus transferring the torque of the motor to the saw headset.
It is worth noting that all chainsaws are classic devices, driven by a gasoline engine.
Electronic chain saw ignition diagram.
In the construction of chainsaws, single-cylinder engines that run on high-octane gasoline are used. The power unit has no gearbox. It is a single-stage gear that drives the chain. Simple design ensures reliable and trouble-free tool operation even in harsh conditions.
In addition to the above-mentioned components, the chainsaw design includes an air purification system, which is fed into the engine for the fuel mixture preparation, a guide bar with a saw chain mounted on it, a starter, which ensures the start of the chainsaw power plant, a chain tensioning mechanism, an ignition system, an exhaust silencing system.
The design of the chainsaw includes a clutch mechanism, which consists of such elements as:
- slipper disk;
- pressure plate;
- mechanism’s protective cover;
- release lever;
- engaging fork;
At minimum revolutions of the power unit, the chainsaw clutch is drawn to the center of the shaft by a spring device and does not transmit torque to the drum. At the time when the motor speed begins to reach the values at which the breakout force exceeds the force of the spring device, the friction type segments begin to press against the inner surface of the drum mechanism, which contributes to the rotation of the drum of the Chinese chainsaw.
The drive sprocket, which is responsible for moving the saw chain, starts to rotate.
Husqvarna, STIHL, Partner and most other brand name chainsaws have a centrifugal clutch. It is activated automatically when the motor reaches a certain speed.
The clutch basket is shaped like a disc. It has movable friction plates that can move in a radial direction. In normal position they are pressed against the center by built-in springs without touching the chain drive sprocket drum.
When the engine reaches a certain speed, centrifugal forces act on the shaft on which the clutch basket is mounted at a given speed, exceeding the force of the springs. The friction plates move laterally by pressing against the inner surfaces of the sprocket drum which starts rotating at a desired frequency. Such a system can protect the engine from serious damage if the chain jams.