In addition to the above units, chainsaws have a cleaning system for the air supplied to the carburetor, a tire with a saw chain, a starter, a chain tension mechanism, ignition, a silencer, etc.
The chainsaw engine has a maximum speed of about 13,500 rpm. This imposes stringent requirements on the oil added to the fuel mixture.
At low speeds, elements with friction pads (1) having a degree of freedom in the radial direction are attracted to the center of the shaft by springs (2) and do not transmit rotation to the drum (3) connected to the chain drive sprocket. When the engine speed of the chainsaw reaches values at which the centrifugal force exceeds the force of the springs, the friction segments are pressed against the inner surface of the drum and begin to rotate it. As a result, the drive sprocket starts to rotate, driving the saw chain.
As you can see in the photo, the sprocket is behind the clutch.
For other chainsaws, the sprocket may be on the outside of the clutch.
The main advantage of clutches of this type is that when the chain is jammed, the clutch of the chainsaw slips without shutting down the engine and without breaking the mechanisms that transmit movement from the engine to the chain.
Electronic ignition of a chainsaw includes a flywheel (1) with built-in magnets, an ignition module (2) with an electronic circuit, a spark plug (3) and a high voltage wire (4). A rotating flywheel with magnets induces an emf in the module, which is converted using an electronic circuit into electrical signals supplied to the candle. As a result, a spark ignites between the contacts of the latter, igniting the air-fuel mixture.
Below is a diagram of another carburetor chainsaw.
Carburetors have a throttle valve that allows lean or enrich the mixture depending on working conditions. For fine tuning, there are several screws that can be used to adjust low and high engine speeds, as well as idling. An air filter is installed on top of the carburetor to clean the air entering it.
So that, as the fuel mixture is used up, the fuel tank is filled with air and negative pressure is created in it, which will not allow fuel to flow from it into the carburetor, and at the same time so that fuel does not flow out of the air hole, a cover is made in the filler cap breather. And by the way, if the breather clogs up with dirt, then the chainsaw stalls.
From the tank, fuel is pumped through a hose freely hanging in the tank. Due to this, regardless of the position of the chainsaw, the hose is always immersed in fuel. A fuel filter is attached to the inlet end of the hose. Fuel pumping pump inside the carburetor.
To facilitate starting, part of the chainsaws is equipped with a manual pre-pump. primer. When starting a chainsaw with a primer, the carburetor is filled with fuel in advance (excess fuel flows back into the tank). Thanks to this, the engine starts faster, because the stage of filling the carburetor with fuel has already been completed, which without a primer is performed by the carburetor pump due to the starter.
Air purification system
Pre-filters can have a different design and consist of several elements, in particular, from a mesh (2) and snow (1) filter (see photo below).
The latter prevents the ingress of snow into the air purification system and is used only in winter, when it is removed at plus temperature.
Some chainsaw models use pre-treatment air purification using centrifugal forces. The air flow is twisted by a flywheel impeller, as a result of which impurities are thrown away from the suction pipe, which goes to the fine filter.
Fine filters are made of diffusion foam, nylon mesh and other materials.
During the operation of the chainsaw, the air in the zone of its operation is highly contaminated with sawdust and wood dust. Excessive pollution of the filter reduces the amount of air entering the carburetor, which leads to enrichment of the mixture and a decrease in the power of the chainsaw. Therefore, regular cleaning of the filter is necessary. It should be carried out not only when the chainsaw is being disassembled for the purpose of repairing it, but much more often, after any lengthy and dirty work. Cleaning is carried out by a method that depends on the type of filter material. most often by blowing and rinsing.
The starter mechanism consists of a drum (1) with a cable (2) and a handle (3), and of a frame (4) with a return spring. When the handle is pulled up sharply, the drum ratchet engages with the teeth on the engine shaft and cranks the crankshaft. When you release the handle, the return spring returns it to its original position.
It takes some effort to crank the crankshaft at the speed at which the engine starts. It is often not possible to start a chainsaw with one jerk, you have to pull several times. To facilitate starting, various methods are used. enriching the fuel mixture with a carburetor damper, or reducing the pressure in the cylinder using a decompression valve (to facilitate cranking). The valve is automatically closed when the pressure in the cylinder increases when the mixture ignites. Sometimes, an additional spring is used in the starter mechanism, which, when pulling the cable, first contracts, and then abruptly opens, spinning the motor.
The main and most complex links in the chain are cutting links, which are divided into right-handed and left-handed. The upper face of the tooth is the widest of all elements. It provides a wide cut, eliminating the jamming of the remaining links.
The shape of the cutting teeth can vary significantly between chains of different manufacturers. There are two main forms. chipper (a) and chisel (b). However, there are various intermediate contours of the incisors.
The cutting edges of the tooth. the side and top. are sharpened at a certain angle. For chains of longitudinal sawing it is 10 °, for transverse. 30 °. Longitudinal chains are rarely used. If necessary, longitudinal sawing can also be done with a cross-cutting chain. Read more about the chainsaw sharpening angles in the article Sharpening chainsaw chains.
The main characteristic of a chain is its step. To establish the chain pitch, the distance between the midpoints of the first and third connecting rivets is measured (see the figure below), and this size is divided in half. The result obtained is the chain pitch in mm. However, in most cases, the chain pitch is set in inches. The distance between the midpoints of the first and third connecting rivets is measured because the distances between the openings of the driving links and the cutting links or connecting links can vary in magnitude. The most common chains in increments of 0.325 and 3/8 inch (8.255 and 9.525 mm, respectively). Chains with a pitch of 0.325 are used with engines of low power (volume up to 40-50 cm 3), while powerful chainsaws are usually equipped with 0.404 inch chains (such chains have higher performance). The cut is cleaner and more accurate if you use a chain with a smaller link thickness and a smaller pitch when sawing.
Important characteristics include shank thickness. Five standard thicknesses are available: 1.1, 1.3, 1.5, 1.6 and 2 mm. The most common are chains with a liner thickness of 1.3 mm (0.05") They are widely used both on household and professional chainsaws. The thickness of the guide links must be consistent with the groove width of the guide bar so that the saw chain fits the guide bar exactly.
Video: Where is the Chainsaw Breather
Chain manufacturers use different technologies for their manufacture and use different materials. The defining characteristic of the latter is not hardness (too hard teeth are difficult to grind by hand), but viscosity and impact resistance. They determine the durability of the chain. Therefore, in the manufacture of cutting teeth wear-resistant alloy steels are used. Cutters are often chrome plated to increase surface hardness. Some firms use bead blasting to increase the viscosity of the teeth.
To guide the chain, the tire has a guide groove at its periphery, in which the driving links of the chain are moved. The groove in the groove serves as a conduit for oiling the chain. The main parameters of the tire include:
- The dimensions of the connecting holes (a), depending on the type of chainsaw.
- The width of the groove (b), which should correspond to the thickness of the shanks of the chain used. The width of the groove of the tire is only a few hundredths of a millimeter greater than the thickness of the driving links of the respective saw chains. Thanks to this, precise lateral guiding of the saw chain is achieved.
- The sprocket pitch (c) also determines the compatibility of the circuits used with the bus.
- Cutting length (g), which determines the size of the processed material. the diameter of the tree trunk, etc.
The brake circuit can be contact and inertial. The first occurs when the brake stop (1) is pressed on the worker’s hand, which occurs spontaneously when the saw is thrown away. The displacement of the stop resulting from this causes the brake band (2) to be tightened on the clutch drum and stops, as a result of which the saw chain also stops.
The inertial application of the brake is based on the inertial forces arising from a sharp blow to the tire acting on the brake elements, which leads to the same result as in the first case. tightening the brake band and stopping the chain. Inertial brake application is faster than contact. However, the second is more reliable. Any preparation for work, as well as the assembly of a chainsaw after its repair or maintenance, should end with a check of the operation of the chain brake. If it does not work, the saw should be considered malfunctioning.
Chain tensioning mechanism
For added convenience, the chain tension screw may be located on the side.
Chain lubrication system
Oil pumps have a different design (piston or diaphragm type) and are made of different materials (metal or plastic). They are driven by a gear train, which receives its movement from the drive sprocket. When the engine is idling (the drive sprocket and chain do not rotate), oil is not supplied. Pump performance depends on the number of revolutions of the drive sprocket; the higher they are, the more oil enters the saw chain. Some oil pumps are equipped with a manual capacity adjustment mechanism. using the adjusting screw (1).
Video demonstrating a chainsaw device:
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A chainsaw is a device that is useful for every host. No matter what model you have a chainsaw, sooner or later you have to thoroughly study it in order to diagnose problems, repair the device yourself. Why is this necessary?
Of course, such a working tool is not safe from breakdowns, but some are not so serious that you contact a service center (where you have to leave a tidy sum). Sometimes a chainsaw can fail due to the banal clogging of the breather. Not sure where the breather on the chainsaw is? You will learn about this and much more from this article.
What is a breather?
This is a part that looks like a standard valve. It plays an important role. it normalizes the pressure in the tank of the chainsaw. Why is it important to normalize blood pressure? In order to answer this question, it is necessary to consider the process of vacuum formation in the tank. This happens when fuel is supplied during the hermetic closure of the gas tank (the pressure on the walls rises). Breather equalizes pressure (relative to atmospheric). Without this small valve, the importance of which many underestimate, proper operation of the chainsaw is impossible.
Husqvarna chainsaw owners can also read the manual. how to clean the carburetor correctly?
Where it is located?
Husqvarna chainsaw breather, as in models of different manufacturers, is in the tank. Sometimes it becomes clogged, which leads to problems with starting the tool or the chainsaw works intermittently or does not start.
How to fix the problem? Here are a few options:
- use compressor to clean;
- clean the small opening of the breather with a needle.
In both cases, you have to get to this detail. Given the structural features of chainsaws, in order to clean the breather, you will have to remove the handle of the device.
How to get to the breather?
You do not need special skill. The easiest way is to refer to the instruction manual of your model. Nevertheless, instructions for dismantling the handle can also come to the rescue.
To get started, pay attention to the preparatory phase.
- To carry out cleaning after dismantling the saw handle was easier, remove the bar and chain, side cover. This is optional, but desirable, because at the same time you can, using a brush and compressor, remove traces of oil, dirt, sawdust.
- Set the dismantled parts aside.
After cleansing, proceed to the removal of the handle.
- The handle is attached to the body with three shock absorbers (all rubberized), but they cannot be removed right away, so for starters we work with plugs made of plastic. Usually they are located in the inner cavity of each shock absorber.
- Take a powerful screwdriver and start squeezing the shock absorbers. Start with the one closest to the handle at the back.
- We remove two screws that will allow us to dismantle the wire rod (it is connected with the carburetor and the gas trigger, it is close to the handle where you removed the first shock absorber).
- At the end, you have a handle that is connected to the shock absorber. Now it remains to unscrew the case (break the inner part of the handle to the side).
- Remove the case from the gum. All is ready!
If you previously dismantled the chainsaw, handle the dismantling of the handle quickly.
Usually after this step the disassembly of the starter follows. But, given the standard structural features of the chainsaw, this step is not necessary for us to get to the breather. Optionally, you can remove the starter, as many sawdust accumulate under it.
Breather Cleaning Procedure
A simple cleaning method is to use a sewing needle. Before cleaning the valve, make sure that it is clogged. This is not difficult to do.
- Remove the carburetor (it must be disconnected from the fuel hose), estimate the number of traces of fuel.
- If the fuel escapes and the breather remains clean, then everything is okay with it and you need to continue the diagnosis. If a weak stream of fuel flows out of the gas line, you can be sure that the breather needs to be thoroughly cleaned.
Important! If after cleaning the chainsaw shows an increase in speed when idling, do not rush to panic and disassemble the tool or take it to the workshop. After cleaning, this behavior of the engine and carburetor (their interaction leads to an increase in idle speed) is considered the norm. If this feature is alarming, you can slightly adjust the idle screw located on the carburetor and marked T.
Is Sapun the culprit of problems with the chainsaw?
At the first sign of a broken chainsaw, do not rush to sin on the breather. Many do not want to immediately begin to disassemble the handle, if they are not completely sure that the culprit is the small valve. Before dismantling the chainsaw handle, exclude the probable causes of device malfunction so that the breather needs to be cleaned. Start small.
- Rate the quality of the fuel mixture. Not all manufacturers provide adjustable jets for chainsaw models. However, in some they can be configured. This gives the "masters" the opportunity to experiment with the composition of the fuel mixture. Perhaps you decided on such an experiment, but after a while you forgot about it, and now blame the tool’s gas tank breather for the tool malfunction. Remember that ideally you need to use the brand of oil recommended by the manufacturer (indicated in the instructions for the device), do not use the old mixture (you need to develop it in two weeks as much as possible). After a month, it will deteriorate and cause malfunctions in the operation of the device.
- Check the candle (perhaps at the time you start the tool you fill it). Inspect this part; it should be clean without a trace of oil. If there is plaque on it, then it should be light, brown indicates a problem with the ignition coil. Keep spare candles on hand to quickly remove this item from the saw problem list.
- Not only the breather can become clogged, but the carburetor jet and fuel filter (that is why after dismantling the handle must be removed and the carburetor to properly clean the surface under it from sawdust). With the cleansing of both nodes, you can handle it yourself.
- Clogged air filter. This filter can become clogged with dust, which will become the main obstacle when trying to start a chainsaw.
Consider the features of your tool model to be able to accurately diagnose the problem. This will help you not only to eliminate it and return to work with a chainsaw as soon as possible, but it will save you from unnecessary fuss (dismantling those nodes that are not connected with a device malfunction).
Typically, a breather is integrated in the unit’s fuel tank cap, so you can easily get to it, and then quickly and efficiently clean the valve.