How to unscrew the sprocket on a chainsaw. The way for a sprocket with a stationary ring

Expert advise: How to correctly remove the chain saw chain sprocket?

Your chainsaw needs regular diagnostics and periodic replacement of worn parts. With regular use, not only the saw headset becomes worn, but also the drive sprocket. In this tool, it acts as a clutch disc, which puts a significant load on it both during start-up and during operation. The sprocket on a chainsaw has a simple design, so it’s easy to do the repair and maintenance with your own hands. In this article, we’ll look at how to determine the degree of wear of this part and perform a scheduled replacement.

Almost all modern chainsaws have a centrifugal clutch system. The specifics of this mechanism is that when the maximum number of revolutions of the gasoline engine is reached, the clutch drum starts automatically, transferring the rotation exactly to the drive sprocket. This reduces the load on the tool’s basic components, extending the life of the tool and maximizing efficiency.

Figure 1. Schematic diagram of the drive sprocket

The clutch drum, where the sprocket is located, can be on the inside or outside of the chainsaw body. there is always a cover on the top to protect the moving parts from dirt, sawdust and dust. The clutch itself is a metal disc in the clutch drum. The whole mechanism is mounted on the engine crankshaft with bolts with springs and friction pads at the ends. When the engine speed exceeds a certain value, the centrifugal force exerts a strong pressure on the inside of the drum. Then the sprocket starts to run. the chain saw starts to rotate.

Important! It is the sprocket that drives the chain of the chainsaw. All parts of this mechanism are closely related to each other, a breakdown of the headset leads to a malfunction of the tool.

A little about how to operate the assembly

Regardless of the brand of the manufacturer (STIHL, Husqvarna, Partner, Patriot, Makita ) chainsaws are divided into household, semi-professional and professional. The difference, however, does not lie in the quality of the assembly or the manufacture of the components, but in the class of the tasks performed, the performance and the long term power of the drive. This predetermines the choice of sprocket drive material for a chainsaw, its design and the design of the saw chain.

The performance of the tool will be determined by the way the chain-and-sprocket pair is operated. In most cases, users use one of the two options:

• The chain is operated up to complete wear of the teeth, and then both the saw blade and the sprocket are replaced at the same time;
• Periodic replacement of chains, which have different pitches, and each chain requires a different drive sprocket.

The choice of option is often determined by the owner’s attitude towards his tool. If it is all the same what you are sawing (wood or steel staples, screws, etc.) and what you want to saw, the chain saw should be used for the first time.), it is possible to choose the first variant. The chain, however, will have to be reworked from time to time, thus reducing the performance of the chainsaw.

It is categorically not recommended to leave the old chain with a new sprocket and vice versa. If the saw blade is worn, there is almost a one hundred percent chance that the tooth pitch will not match. That’s why at the initial start both components of the chain drive will be exposed to considerable dynamic loads. This will either cause the chain to stretch prematurely, “adjusting” to the sprocket, or one of the teeth on the drive sprocket will crack on impact.

Also you should pay attention to the sprocket shaft bearings. Only the crankshaft rotates when the saw is in RPM mode. But all chainsaws also function occasionally at idle speed when the bearing is rotating. Lack of lubricant causes wear in the seating surfaces and. as a consequence. additional tooth wobbling in the still perfectly functional chain drive.

It follows that when replacing the chain and drive sprocket for a chainsaw, it is a good idea to replace the bearing at the same time.

A way to extend the service life of the drive sprocket

In practice to have even wear of sprocket rim a set of several similar chains is used that are changed in turns as cutting edges of saw chain links get blunt. Nevertheless, sooner or later the user is faced with the need to replace a worn part.

The owner’s wish to have a chain of a different pitch would make it necessary to replace the sprocket with a part with a corresponding profile. This requirement applies to the entire range of chainsaws made in Europe and China.

Operational reliability of a European-made saw, when working in demanding conditions of high loads, can deteriorate significantly if you put a Chinese-made sprocket instead of a brand-name part.

Sprocket Replacement Algorithm

During operation of the chainsaw all parts have a right-hand rotation. That is why the clutch locking clutch has a left-hand thread. It is removed with a puller or screwdriver in a clockwise direction.

Replacement sequence of drive sprocket:

During operation, the clutch sticks to the drive sprocket. Therefore, to remove it, you will most often need to do the following.

• Remove the air filter cover and the filter;
• To gain access to the engine cylinder, unscrew the spark plug;
• Turning the shaft, lift the cylinder to the upper position, pulling it back 5-10 mm;
• Fix the crankshaft with a tight cord, which fills all the internal space above the piston;
• With a special puller, turning it clockwise, remove the clutch; in the absence of a puller operation can be carried out with a screwdriver and a medium-sized hammer.
• Slightly tap the clutch clockwise, then unscrew it by hand. In this case, we advise to be very careful not to damage the clutch and not to leave burrs on the metal;
• Remove the drive sprocket inspect it, then inspect the needle bearing and cage;
• Replace the worn sprocket with a new one;
• Reassemble the saw in the reverse order. We advise to conduct all repair works in clean and well-lit place, carefully and cautiously;

Important: when replacing the drive sprocket, remember that there is a driven sprocket on the bar. It is a good idea to replace both parts at the same time to avoid chain wear and other damage to your chain saw.

A few helpful hints:

• When replacing the drive pinion, always lubricate the needle bearing;
• choose a tire and a chain with the same pitch. Otherwise the sprocket on your chainsaw will flatten and quickly become unusable;
• Watch how the chain saw is cutting. If the chain starts to wedge, lead sideways, the kerf becomes uneven. inspect the sprocket, obviously it is worn and needs to be replaced;
• Always clean your chainsaw after use. Periodically remove the side cover and remove the sawdust. If it is not, debris will mix with oil and get on the chain and sprocket.

The chainsaw clutch system

On chainsaws Husqvarna, STIHL, Partner and most models of other well-known brands, a centrifugal type clutch is installed. It turns on automatically when the engine reaches a certain speed.

The clutch housing is shaped like a disk. It has movable friction pads that can move in a radial direction. Normally they are pressed against the center by the built-in springs, not touching the sprocket drum of the chain drive.

When the engine reaches its normal operating mode at a given RPM, centrifugal forces act on the shaft on which the clutch basket is mounted, exceeding the force of the springs. The elements with the friction liners move to the sides, pressing against the inner surfaces of the sprocket drum, which begins to rotate at the desired frequency. Such a system can save the engine from serious damage in the event of chain jamming.

Depending on the model, the sprocket is located on the outside or inside of the clutch assembly. the entire assembly and part of the guide bar are covered with a protective cover for safety.

Algorithm for replacing the clutch drum with sprocket by yourself

How to change a chain sprocket on your chain saw or chain saw. Read more about it below.

The following steps are required for the sprocket replacement procedure:

• remove the chain brake cover and pull it toward you (avoid contact of the brake band with the clutch parts);
• Use a wrench to loosen the nuts that hold the chain tension and chain cover in place;
• remove the chain and then the bar, removing debris and filings from the mounting holes;
• Fix the piston in the cylinder with the usual string, but if possible, you need to use a piston stop or a special retainer;
• start rotating the clutch and do this until the piston touches the exhaust port;
• then the stopper or string is lowered into the spark plug hole and there secured by tying a few knots (the stopper will lock itself);
• unscrew the clutch nut (note. the thread of this nut is left, take this into account when unscrewing);
• Hard tools should not be used, so as not to break the soft metal of the clutch nut;
• then the clutch is removed;
• then remove the sprocket pinion itself;
• replace the old sprocket with a new one;
• Reassemble the structure in reverse order.

Changing a chain saw sprocket

A universal wrench is the main tool you will need when replacing the sprocket.

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

• jamming of the chain due to defects that occur during the unit’s operation;
• excessive wear of the sprocket wheel due to continuous use of the machine.

High sprocket wear due to excessive force applied to it during wood sawing operations will occur if the chain saw is used frequently. There are two ways in which the machine can be operated

in the first type of operation, the chain is used until it is completely worn out. This method has several disadvantages. The main disadvantage is the problem with monitoring 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, thus extending the life of the machine before a repair consisting of replacing the sprocket. in addition to wear on the sprocket, do not forget the bearing that is installed in the sprocket. This component works at any engine speed. When replacing the sprocket, the bearing must also be replaced at the same time.

The clutch and sprocket assembly must be replaced in a timely manner. if the tool is not repaired in time, increased vibration occurs during operation, resulting in increased wear of the bearings installed in the internal combustion engine on the crankshaft halves. The sprocket teeth should not have a wear limit of more than 0.5 mm. Sprocket life is twice as long as life of one chain, so you should use two chains while working. After reaching the end of the chain life the chains and drive sprocket should be replaced at the same time.

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Replace a Worn Sprocket in a Chainsaw

The chain saw or electric chainsaw chain sprocket is one of the most important parts of the saw. The main function of a chainsaw sprocket: to transmit engine torque to the saw chain.

This transmission is through a centrifugal clutch. Sprockets are divided into professional and household sprockets, like chains.

The chainsaw and wood sawing operations will gradually wear out the drive sprocket and the chain.

Husqvarna chain sprocket

Let’s learn more about why a worn chainsaw or electric chainsaw sprocket needs to be replaced and when it’s best to do it.

The following are some telltale signs that the sprocket needs to be replaced:

• Your chain saw has been changed twice (one of the rules of chain saw and electric saw operation 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 have installed a new chain to which the old sprocket does not fit (this part is not universal and also has its own pitch, in addition, the chain steps of the drive and idler sprockets must match, otherwise the tool will not work);
• you are using a different bar, a shorter or longer.

Why you need to replace the sprocket?

You should remove a worn sprocket for the following reasons:

• with the old sprocket, the saw chain will stretch very quickly. after just a few uses the chain will hang loose and tensioning will not help;
• If you put the new chain on the old sprocket, the chain will run smoothly, the quality of the cut will deteriorate and the chain will run sideways when you cut;
• The overall wear on the chainsaw will accelerate, the tool could fail at any time;
• The chain can break or the chain can jam during operation (risk of hand injury and damage to the body of the chain saw or chainsaw);
• the bar will become hotter and the chainsaw will overheat quickly;
• the stress on the engine and housing will increase.

Important! Do not substitute sprocket sizes for your own needs when repairing, use the manufacturer’s standard. Unauthorized substitutions will cause the chainsaw or electric saw to perform poorly.

Is there any way to extend the life of an existing sprocket??

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

• use more than one chain (preferably three). This method is the gentlest and most convenient for the chainsaw owner in that there is no need to constantly retighten the chain worn by intensive work. Operating three chains alternately will preserve the sprocket’s life and delay its replacement;
• Quality sprocket bearing maintenance. This part plays an important role in the functioning of both the drive sprocket and the motor. For lubrication, it is recommended to use a special lubricant. The sprocket bearing is not engaged all the time, but only at idle speed and therefore requires periodic lubrication. You can use tire nose grease, such as standard Repsol or Husqvarna grease.

What tools do you need to change the chainring?

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

• a special key for the removal of this part (usually supplied with expensive brand name chain saws, cheap saws are not equipped with such a key);
• poke out of aluminum or copper (only soft metals and only in the absence of a wrench);
• hammer (to hit the hammer while unscrewing the sprocket);
• a flathead screwdriver to tighten the nut;
• grease for the sprocket bearing.

design problems, differences between different models

Branded chainsaws have a special design, which does not allow to replace the worn drive without dismantling the clutch and other parts of the chainsaw. That is, the saw has to be almost completely disassembled. modern models of expensive chainsaws are always equipped with a special wrench.

Changing the chain saw sprocket

Also the chainsaw owner 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, if the chain teeth are worn, you must unscrew and replace the drum, one piece with the drive. On newer models, the sprocket can be replaced separately.

Algorithm of independent replacement of the clutch drum with sprocket

How to replace the drive sprocket on an electric chainsaw or chain saw. here’s how to do it in detail.

For the sprocket replacement procedure, you need to do the following steps:

• remove the chain brake cover and pull it toward you (avoid making contact between the brake band and the clutch parts);
• Use a wrench to loosen the nuts that hold the chain tension and the chainsaw cover;
• remove the chain and then the bar, removing debris and filings from the mounting holes;
• fix the piston in the cylinder with normal cord, but if possible, use a piston stopper or special retainer;
• start rotating the clutch and do this until the piston touches the outlet hole;
• After that, a stopper or string lowered into the candle opening and there fix, tying a few knots (stopper will fix itself);
• unscrew the clutch nut (note. the thread of this nut is left, take this into account when unscrewing);
• do not use any hard tools so as not to break the soft metal of the clutch nut;
• then the clutch is removed;
• then remove the sprocket pinion itself;
• replace the old sprocket with a new one;
• Reassemble the construction in reverse order.

Algorithm of replacement of the clutch drum

Regular inspections are essential for the trouble-free use of the chainsaw.

When replacing the clutch drum only a certain type of fixture should be used for installation. When replacing the Print Drum (Cylinder) the bearings of the element must be changed at the same time.

To perform the repair work it is necessary to purchase a special repair kit, which contains a driving sprocket and a bearing. After you have purchased the repair kit, prepare the necessary materials and tools for the repair. The basic tools you will need when making repairs are the following:

• universal wrench that comes with the chainsaw;
• The piston stopper, can be made of plastic or metal;
• A special puller of the centrifugal mechanism or the clutch drum.

The work procedure consists of several steps. Each step has its own characteristics, depending on the design features of the chainsaw, but the scheme and sequence of operations is the same for any model of machine.

The sequence of repair work

The first step is disassembling of the saw headset, the guide bar cover is removed. Dismantle guide bar and saw chain after removing cover. Use the universal spanner provided with the machine to unscrew the clutch nut.

After removing the saw chain and guide bar, the air filter is removed. Then the spark plug is disassembled. The previously prepared engine piston retainer is installed in place of the removed spark plug. The stopper allows the piston to be locked in the cylinder and prevents the crankshaft from turning. The clutch should be removed with a puller in the socket of the allen key. All actions should be carried out in a clockwise direction.

After removing the clutch access to the internal parts of the device opens, that is, after removing the clutch you can remove the sprocket.

After removing the clutch drum, depending on the type of clutch drum, inspect and check the pinion and sprocket. Depending on the design of this unit, wear and tear elements are replaced. Special attention should be paid to the centrifugal springs and cams when making repairs. If wear is detected, they must be replaced.

If you can make no problems with the components, put them on the chain saw in the reverse order. First unscrew the piston lock and pull the starter cord out, then put the piston lock in place. This intricate sequence of operations gives you the opportunity to clamp the centrifugal mechanism to the crankshaft of the machine. The clutch is put in place and clamped with the Allen wrench that came with the chainsaw. Wrench clamping should be done counterclockwise.

The last step of the repair work is to install the remaining structural elements.

When replacing the sprocket, all work should be handled with care and attention. All repair work must be carried out with special tools, otherwise the centrifugal mechanism or the saw chain could be put out of order.