the principle of operation of the general and individual nodes


Gasoline saws are used in the construction of log cabins, logging, clearing the area of ​​thickets, and replenishing the stock of firewood. They allow you to effectively work with wood. The relatively simple structure of the chainsaw makes it a durable and reliable tool, both for domestic use and for professional activities. Structurally, the product belongs to the category of machines equipped with an internal combustion engine (ICE). In many cases, this is a two-stroke single-cylinder engine. The user needs to know the structure of the tool and the features of the functioning of its individual components — this will help to properly perform maintenance and, if necessary, make repairs on their own.

General chainsaw device

There are many models of gasoline saws on the market from different brands. Products from different manufacturers differ from each other in design and technical characteristics that determine the ergonomics and functionality of the equipment, but the tool has the same device.

The chainsaw consists of the following structural elements:

  • internal combustion engine;
  • carburetor;
  • tires;
  • chains;
  • handles;
  • clutches;
  • starter;
  • ignition systems, fuel supply, air filtration and chain lubrication;
  • muffler;
  • chain brake and its tensioning mechanism.

The chainsaw circuit is shown in the photo below.

Chainsaw scheme

Carburetor ICE runs on a mixture of oil and gasoline. A diagram of his workflow is shown in the photo below.

Carburetor ICE

The components of the fuel mixture are mixed proportionally. The ratios between them are indicated in the user manual (oil to gasoline from 1:20 to 1:50, respectively). The duration of operation of the tool without repair depends on the quality of the fuel.

Modern gasoline saws from the expensive category often have an oil reservoir. Mixing it with gasoline in such modifications occurs automatically.

See also: what kind of gasoline to fill in a chainsaw, and how to choose oil.

The two-stroke motor is capable of speeds up to 13.5 thousand rpm. It can be located on the tool vertically or horizontally. The first option for placing the internal combustion engine is typical for many professional models of large chainsaws. The muffler is located in front of the engine.

If the motor is located horizontally, then gasoline saws are compact in size. The mass of such tools is also small. These features make horizontal motor products popular with farmers, lumberjacks and other workers using hand saws.

The design of the chainsaw involves the presence of two handles: front and rear. On the latter there is a switch, gas and safety levers. Implemented in the tool vibration and kickback protection. The first is due to the presence of rubber gaskets between the handle and the saw. Some models also have springs that dampen vibrations. A special brake or shield can protect against a kickback.

See also: how to choose a chainsaw.

Design and operation of individual units

The individual components of the gasoline saw discussed above, in turn, consist of various parts. To independently repair equipment, you should know the design and operation of the main systems.

Ignition system

Initially, the ignition system of chainsaws was contact type. Now it is practically not used. Modern manufacturers equip their equipment electronic ignition (pictured below disassembled). For this reason, there is no need to regularly clean the contacts and set the required distance between them.

Ignition system

The ignition system, due to which a spark is generated during engine start, consists of the following parts:

  • magneto;
  • candles;
  • electronic block;
  • electrical wiring;
  • motor on/off buttons.

The appearance of the elements of the ignition system of one of the models of chainsaws from the Shtil brand is shown in the following photo.

Appearance of the ignition system

Magneto — This is an alternating current generator that supplies voltage to a candle. It can be of two types:

  • contact;
  • contactless.

Schematically, ignition systems with non-contact and contact types of magneto are presented below.

Ignition system with non-contact and contact magneto

Any type of magneto includes the following details:

  • flywheel;
  • permanent type magnet;
  • a coil consisting of windings with a core.

Part electronic block diodes, resistances of various sizes, thyristors, capacitors are usually included. The connection diagram depends on the saw model.

Ignition works according to the following principle:

  • when the flywheel rotates with a permanent magnet attached to it, an electromotive force is induced in the system;
  • the current that has arisen in the circuit is converted by the electronic unit into electrical signals;
  • they are transferred to the candle;
  • a spark forms between its contacts, which ignites the fuel-air mixture.

The ignition is initially adjusted so that sparking occurs when the engine piston does not reach its top dead center by about 3-4 mm. If you navigate along the circumference of the crankshaft, then this corresponds to an angle of 28 degrees.

Candle consists of the following parts:

  • central and side electrodes;
  • corps;
  • insulator.

By the condition of the candle, it is possible to visually diagnose malfunctions of the ignition system.

Thus, due to the presence of ignition, the fuel mixture ignites, which ensures the transition of the motor to a working state. Periodically, the system needs adjustment, which is easy to carry out on your own.

carburetor assembly

The carburetor is required for the continuous operation of the internal combustion engine. It consists of the following structural elements:

  • one-piece cast aluminum body;
  • jets, which are valves that regulate the amount of fuel;
  • diffuser;
  • float chamber;
  • atomizer.

carburetor assembly

In the carburetor damper installed, which regulates the supply of atmospheric air, an impulse channel, a diffuser, an inlet fitting, two screws (idle and main). Very often, chainsaw manufacturers equip their products with carburetors from popular brands.

Most chainsaw models are equipped with identical (in their design) carburetors. Schematically, their device is shown in the photo below. Only rare cheap Chinese-made modifications can be distinguished by the absence of a number of parts in the carburetor assembly.

Carburetor diagram

In order to properly adjust the carburetor of a gasoline saw, you should understand the principle of its operation, which is as follows:

  • when the engine is started, the air damper located on the body in its lower part opens;
  • due to the movement of the piston (stroke), a vacuum is created inside the float chamber, as well as in the air channel;
  • this causes the air mass to be sucked in through the diffuser;
  • from the gasoline tank, the fuel mixture penetrates into the float chamber, passing through the fitting;
  • then gasoline in the diffuser is mixed with atmospheric air, resulting in a fuel-air mixture;
  • then it enters the intake channels;
  • from there the mixture enters the combustion chamber.

Using a damper, it is possible to enrich or deplete the fuel with air, that is, to adjust the intensity of its supply in accordance with operating conditions. With the help of screws adjust the speed of the motor. The speed of gasoline entering the diffuser from the chamber is adjusted by the jet. The incoming air is cleaned by a filter mounted above the carburetor.

The health of the carburetor assembly determines the performance of the chainsaw and the performance of its motor.

clutch mechanism

chainsaw clutch centrifugal type. It works automatically when the motor speed reaches the required number of revolutions.


Schematically, the operation of the centrifugal clutch is shown further in the photo, where the following design elements correspond to the numbers:

  • friction linings;
  • springs;
  • drum.

Schematically the operation of a centrifugal clutch

At low engine speeds, the linings, which can move radially, are pulled up to the shaft by springs. At this time, they do not rotate the drum connected to the chain sprocket. When the internal combustion engine develops the speed at which the force from the springs becomes less than the acting centrifugal force, the friction linings set the drum in motion, pressing against its inner surface. In this case, the sprocket that drives the chain comes into rotation. It can be located in different models of gasoline saws in front of the clutch or behind it.

The main advantage of centrifugal clutches is that they slip when the chain jams without stalling the motor.

Fuel system

The fuel system device is shown in the diagram below.

Fuel system device

The numbers correspond to the following elements:

  • fuel filter;
  • carburetor;
  • fuel pump (primer) manual type.

Gasoline is in the tank, from which it enters the carburetor assembly through a hose. The simplest options do not include a pump. Fuel filter located at the end of the hose immersed in gasoline. Its appearance is shown in the photo below.

Fuel filter

When fuel is consumed, a negative pressure is formed in the tank due to its filling with atmospheric air. This leads to the fact that the flow of gasoline to the carburetor assembly stops. To avoid this phenomenon, the tank cap equipped with a breather: If it is dirty, the instrument will stop.

The primer on the chainsaw makes it easy to start the chainsaw. The carburetor department is filled with fuel in advance, which allows you to quickly start the engine, and also leads to a decrease in the load on it.

Air purification system

In order to obtain a fuel-air mixture of proper quality, clean gas is required. The presence of impurities in the air can disrupt the functioning of the internal combustion engine of the tool. Therefore, chainsaws are equipped with a preliminary and fine filter system to remove polluting particles.

Air purification system

Pre-filtering is usually done with mesh filter.

During operation at low temperatures, an element is also installed that retains snow. But because of it, the air supply worsens, causing a drop in the power of the operated unit.

Chainsaw design

Filters designed for fine cleaning (photo below), are made from nylon mesh or foam rubber or from materials similar in characteristics.


Some models of saws have a system for cleaning the incoming air centrifugal type. It is installed instead of the pre-filter element. The meaning of the functioning of such cleaning is that the incoming air flow is twisted by a flywheel. In this case, polluting particles are thrown away from the nozzle leading to the filter.

chainsaw filter

Contamination of the filter elements leads to a decrease in the volume of atmospheric air entering the carburetor assembly. This causes a drop in the motor power of the saw. Because of this reason, filters that purify the air of impurities should be clean regularly washing or simple blowing. The appropriate method is determined by the material from which they are made.

Starter device

The chainsaw starter is designed to start its motor, which is carried out by cranking the crankshaft. In this case, the air-fuel mixture, which is in the engine, is compressed by the piston. A spark causes it to ignite, as a result of which the internal combustion engine starts.

The components of the starter are:

  • lever;
  • cable;
  • drum;
  • return spring.


With a sharp pull of the handle with a cable, the drum engages with the shaft. The latter starts to scroll. After releasing the handle, the spring ensures that it returns to its original position. To turn the shaft at such a speed at which the motor will start, some effort should be made: in most cases, you will need to pull the handle several times.

In order to make the process of starting the engine easier, in practice, for example, the following methods are used:

  • using a damper, enrich the fuel mixture;
  • using a special valve, they lower the pressure inside the cylinder.

To facilitate starting, some models of starters also have a additional spring. It first compresses when the cable is pulled out, and then unclenches, thereby spinning the engine.

Lubrication mechanism

The guide bar, like the chain, is made of metal. When the tool is turned on, the chain begins to rotate at high speed. As a result, friction material overheating. That is why it is recommended to cool the chain during operation. If this is not done, then it will wear out very quickly and, as a result, the tire will also fail.

To prevent this from happening, all models and types of chainsaws (and electric ones too) have mechanisms responsible for lubricating the chain. Such devices perform several tasks at the same time. First, they cool the chain material during operation. Secondly, they allow you to minimize the negative impact of chain friction on the guide bar.

chainsaw chain lube

The mechanism responsible for chain lubrication in a chainsaw is oil pump. There is no need to turn it on separately — the work is done automatically. When the tool motor is turned on, oil begins to flow to the chain. In this case, the frequency of lubrication depends on the speed of the device. The pump itself is called a plunger or piston pump.

To understand the principle of operation of the oil pump, it is necessary to study in detail its main components.

  1. Oil pump body. Made of aluminum or plastic. The second option is most often found in models intended for home use.
  2. Plunger. Part required for pumping oil. It has a cylindrical shape, driven by a worm gear.
  3. Channels. Connect the oil supply and exhaust channels.
chainsaw oil pump

Chainsaw oil pump

In general, the action of the plunger looks like this.

  1. On the one hand, the plunger shaft rests against the stem. In some models, it can be adjusted. At the shaft itself, the wall has a wave-like shape.
  2. On the reverse side of the plunger is its working part, which has a protrusion or cutout at the end of the structure.
  3. When the plunger moves through the supply channel, oil enters from the oil tank, and then, through the outlet pipe, it is fed to the tire, which lubricates the chain.
oil pump plunger

Chainsaw Oil Pump Plunger

The schematic diagram of the oil pump is extremely simple, and it is thanks to this that the cost of the chainsaw remains at a fairly low level. In this case, the part can almost always be repaired, except for the case when the undulating wall wears out. In this case, the node is recommended to be replaced with a new one.

In some models, in order to independently adjust the oil supply, the design of the oil pump provides for the presence adjusting screw. If the part is out of order, then it is forbidden to work with a damaged tool. Checking the health of the pump is quite simple. It is enough to put a blank sheet of paper next to the tire, start the chainsaw and turn on the gas a couple of times. If the mechanism is in working condition, oil stains will appear on the paper.

See also: how to choose a chainsaw chain.

chain brake

The chain in a gasoline saw is a traumatic factor. When it rotates, a short, gentle touch on it is enough to cut yourself or get a more serious injury. For this reason, a chain brake is provided on the chainsaw, which quickly stops it if reverse blow.

chain brake

There are two types of brakes:

  • inertial, responsive to the force of inertia that acts on the brake mechanism;

Inertia brake

  • contact, stopping the chain during a reverse impact after the brake stop is pressed.

contact brake

Inertial type brakes work much faster than contact counterparts.

Before using the chainsaw, for safety reasons, you should always check the operation of the chain brake. If it does not work, then the tool should not be used until the problem is fixed.

Chain Tensioner Device

The chain tensioner is a very simple design, regardless of the tool model. It only consists of pin and adjusting screw. The screw is tightened or loosened with a screwdriver or wrench. With its help, the pin moves in a special groove of the chainsaw. In this case, along with the movement of the pin, the chain is tensioned.

keyless chain tensioner

Some modern models have a keyless chain tensioner.

The location of the adjusting screw usually depends on the specific model of the device. It can be located on the side, below or behind the working unit.

It is not recommended to neglect the tension setting. It is best to do this every time before starting work.

If you work with a loose chain, it may come off the grooves and cause injury to the person using the chainsaw. However, this does not mean that it is necessary to tighten the chain very strongly. If it is too tight, then there is a high probability that it will work under maximum load, as a result of which a break may occur. This is fraught with serious injury.

See also: how to use a chainsaw correctly.

The general principle of operation of a chainsaw any model is simple: a running engine rotates a chain that cuts wood. The functioning of the tool depends on the condition of its individual parts, the quality of the fuel mixture, the degree of purification of the incoming air. In order for the equipment used to last as long as possible, it is necessary to organize regular maintenance, while relying on the instructions contained in the operating instructions.

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