What should be the compression in a chainsaw

What should be the compression in a chainsaw

A chainsaw is a simple device that, with proper care, can last for a long time. At the same time, the saw is a tool subject to various loads and, therefore, breakages still occur. You will learn about what caused a certain malfunction and how to fix it from this article.

compression, chainsaw

Depressurization of the carburetor and blockage of the nozzle

Over time, the screws that secure the carburetor cover may loosen or the gaskets become unusable. A clogged filter or its improper replacement can lead to clogging of the nozzles. All this also negatively affects the operation of the chainsaw and reduces the service life.

To prevent this, it is sufficient to periodically inspect the saw and, if necessary, evenly tighten the screws.

Chainsaw loses power under load

If in the process of work the saw power disappeared somewhere, then the problem should be looked for in the following places:

  • In the muffler. He, as you already understood, tends to clog.
  • Clogged fuel filter.
  • In a poorly functioning fuel pump.

All chainsaw malfunctions can be divided into two main groups: engine problems with all its components and systems (ignition, fuel supply system, cylinder-piston group, exhaust system) and malfunctions of other components (chain brake, lubrication system, clutch, tire, etc).

Malfunction of other systems

In some cases, users of chainsaws note other problems that do not significantly affect the operation of the tool.

How to check the compression on a chainsaw

With a compression level below 8 atmospheres, the engine will not have enough power, which means that the chainsaw will not be able to fully function.

  • Remove the protective cover and unscrew the spark plug.
  • Insert the tip of the compression tester into the hole where the candle should be located.
  • Using the starter cord, rotate the piston and memorize the maximum readings of the measuring device.

How to clean an air filter

If sufficient air is not supplied, the fuel mixture becomes too rich, which leads to a malfunction of the engine. Regular purging of the air filter, and in especially advanced cases, washing in soapy water will avoid such problems.

Please note that rinsing in acetone, gasoline or other aggressive solutions is not allowed. This can lead to a violation of the integrity of the filter element.

How to clean an air filter

If sufficient air is not supplied, the fuel mixture becomes too rich, which leads to malfunction of the engine. Regular purging of the air filter, and in especially advanced cases, washing in soapy water will avoid such problems.

Please note that rinsing in acetone, gasoline or other aggressive solutions is not allowed. This can lead to a violation of the integrity of the filter element.

Chainsaw does not idle

In this case, you should start looking for a malfunction with the filter elements. For the most part, it is precisely because of the decrease in the throughput of the air and gasoline filters that the idle speed begins to “float”.

If everything is in order with the filters, then it is necessary to check the components of the gas supply system, as well as to make sure that there is no spontaneous change in the carburetor settings.

Malfunction of undefined category

In some cases, the owners of chainsaws have to solve more complex problems in order to fully restore the functionality of their cutting tool.

Question: “What kind of compression should a chainsaw engine have?”

Answer: Normal compression for chainsaws is 8-12 atmospheres (0.8-1.2 MPa). With compression below 8 atmospheres, the engine will not deliver the required power, the torque will not be enough for the stable operation of the chainsaw. How to measure the compression in chainsaw engines? This requires a compression meter. a device for measuring compression. Measurements are carried out on a hot engine. Sometimes, for diagnostics, measurements are also taken on a cold one, in order to establish the cause of the malfunction by the difference in results.

Step by step: Remove the chainsaw cover. We unscrew the candle. It is highly advisable to dismantle the carburetor or remove the air filter. After that, the tip of the compression meter is inserted into the spark plug hole of the chainsaw engine and with the starting cord we rotate the piston until the maximum compression meter readings are reached.

The most common cause of loss of compression is ring wear. This can be checked very simply. after you find that your chainsaw has a compression ratio below normal, fill the cylinder with 10-20 milliliters of oil and check the compression again. If the indicators have increased, then the matter is in the wear of the rings.

Watch a video about measuring the compression in chainsaws:

Engine malfunctions

When repairing a chainsaw with your own hands, it is necessary to act in an exclusionary way. to inspect alternately all possible prerequisites for a malfunction, starting with those whose verification and elimination takes the least time (for the device and operation of a two-stroke motor, see here).

Ignition system. Almost all types of engine problems listed above can be caused by faulty ignition systems. Therefore, when they occur, it makes sense to start troubleshooting with a candle. This is all the more justified since the state of the latter can provide useful information about the operation of the fuel system. So, if a problem occurs, you need to unscrew the candle and inspect it.

See also  Gasoline to oil ratio for a Husqvarna chainsaw

The wire is disconnected and the candle is unscrewed with a special key.

If the spark plug is dry, this means that the problem is most likely not in the ignition system, but in the fuel mixture entering the cylinder. You can wrap the spark plug back and start working on the fuel system. If the spark plug is heavily splashed with a fuel mixture, then there is an excess of it. This can occur from a misalignment of the carburetor or a violation of the starting rules. The spark plug is wiped and dried, the cylinder is drained by shutting off the fuel supply and operating with the starter to ventilate the combustion chamber and remove excess fuel. Then put the candle in place and repeat the start.

The presence of a large amount of black carbon also indicates a malfunction in the fuel system.

The ratio between oil and gasoline in the mixture may be disturbed, the carburetor is not adjusted, or poor-quality oil may be used. The candle is washed in gasoline, cleaned with a needle or an awl from carbon deposits, the electrodes are cleaned with a fine sandpaper and installed in place.

In all these cases, it will not be superfluous to check the gap between the spark plug electrodes. Depending on its brand, it should be in the range of 0.5-0.65 mm. It is also necessary to check the spark plug gasket. If it is worn out or damaged, the tightness of the combustion chamber may not be ensured, which leads to a decrease in compression in the cylinder and problems in engine operation.

Even if, when checking the spark plug, there is good reason to believe that the problem is in the fuel system, you need to check the spark plug for the presence of a spark. If only to be sure that everything is in order with this. For this:

  • put the ignition cable on the spark plug;
  • using pliers with insulated handles, apply the thread or nut of the candle to the cylinder;
  • pull the starter handle and see if there is a spark or not.

If there is no spark, you just need to replace the spark plug. in general, share the compression. the pressure created in the figure should not be. If the new spark plug does not have a spark either, you need to check the condition of the high-voltage wire for an open circuit and contact with the spark plug.

I periodically monitor the queries of search engines for which visitors come to the site from search engines. For these requests, as well as for the questions asked in the Комментарии и мнения владельцев, I choose the most frequent ones and answer them in the “Chainsaw: Questions and Answers” section. The previous parts can be found here: “Chainsaw: Questions and Answers” “Husqvarna 137e Chainsaw: Questions and Answers.”

So the most popular queries of the last few months:

How to put the piston on a chainsaw correctly

The work on replacing the piston for most models of modern chainsaws is carried out according to the following algorithm:

  • Top and side covers are removed.
  • Unscrew the candle.
  • The handle is removed from the shock absorbers and the handle is detached from the body.
  • The leading sprocket and starter are removed.
  • A piston stopper is installed in the spark plug hole and the nut that fixes the flywheel and clutch is unscrewed.
  • The flywheel, the clutch, the worm drive of the oil pump, located immediately behind the clutch mechanism, is removed.
  • The screws securing the carburetor and air filter are loosened, after which these units are removed together with the engine control lever.
  • The ignition coil is removed, as well as the muffler.
  • The saw is turned upside down and, by unscrewing the screws fastening to the body, the engine is disconnected.
  • The pallet is unrolled and the piston is removed.
  • Since the piston is removed only together with the crankshaft, it is necessary to remove the circlip to disconnect it.
  • The old piston is replaced with a new one, but as carefully as possible. This is due to the high fragility of the compression rings.
  • The crankcase is put in place, and a sealant is used instead of a gasket.

All subsequent actions are carried out according to the reverse algorithm of disassembly.

Chainsaw does not idle

It often happens when, after long transportation and constant use, the chainsaw refuses to idle smoothly. As a rule, this problem is eliminated by adjusting the carburetor.

You can learn how to properly debug the carburetor from this

If the carburetor is tuned like a clock, then you need to check:

  • Fuel system. It makes more sense to start with the fuel pump.
  • Muffler. Chances are high that due to the abundance of accumulated soot, the engine may not function normally.


“Rich” or “lean” fuel mixture will sooner or later cause a breakdown. Perhaps even costly. To prevent this from happening, it will be superfluous to regularly check the filter for scuffs, as well as for a breakthrough of the filter cloth itself.

Necessary skills and tools for repair

Most of the malfunctions of gasoline chain saws can be fixed by hand. True, this requires an understanding of the chainsaw device and how the nodes function among themselves. As for the tool, the most often needed are:

  • screwdrivers (slotted and power);
  • the combination wrench included in the kit or conventional wrenches with different head sizes.

Repair yourself or send to a service center

It should be understood that not every problem can be solved on your own. Not every owner of a chainsaw has a compressor at home or a special device that allows you to create a vacuum and the right pressure, for example, to check the crankcase for leaks. In this case, you simply cannot do without contacting specialized specialists.

What is motor compression?

Compression refers to the value of the highest pressure in the cylinder created when the engine is idle by the starter (for example, when the spark plug is turned off). Compression of the motor should not be confused with the compression ratio. these are different concepts.

To measure the compression, you need to install a compression meter instead of the candle. This device is a pressure gauge connected by a hose with a fitting and a check valve. When the engine crankshaft rotates, air is pumped into the hose until the pressure in the hose equals the maximum pressure in the cylinder. Its value will be fixed by a pressure gauge.

How to check the fuel filter and replace

To check the current state of the fuel filter, you must perform the following steps:

  • Remove the fuel hose from the carburetor fitting and direct it to a working container.
  • Press several times on the so-called “swap”.
See also  How The Chain Should Be Right On Your Chainsaw

If the gasoline comes out unevenly and with jerks, then it’s time to put in a new filter element. This is done quite simply:

  • The fuel tank cap is unscrewed.
  • Using tweezers or any other device, the filter itself is removed.
  • Having disconnected the old filter, you must put a new one and lower it into the fuel tank.

How to measure compression chainsaw 4500

The Chinese lawn mower, according to the client, will not start and there is no spark. Looking for reasons.

Gasoline flows from the chainsaw

If gasoline drops periodically appear on the body of the chainsaw, then it is necessary to check the tightness of the fuel tank. Over time, it may dry out. Or the gasket “hardened” and it can no longer perform its direct function.

If full-fledged gasoline streams appear, then there is a high probability that you will have to change the burst hose connecting the carburetor and the fuel tank.


“Rich” or “lean” fuel mixture will sooner or later cause a breakdown. Perhaps even costly. To prevent this from happening, it will be superfluous to regularly check the filter for scuffs, as well as for a breakthrough of the filter cloth itself.

What compression should be in the engine (for car models)?

Compression. it is a very useful method for diagnosing a car engine. We already know how to check the compression in the cylinders of a car engine, and what compression should be in the most average values. However, we suggest that you now find out more precisely what degree of compression should be specifically for your car model.

So we know what compression is. this is the pressure that is created by the piston in the combustion chamber cylinder when it is at top dead center, that is, at the end of the compression cycle. But there is also such a thing as compression ratio. it is the volume of the entire space in the cylinder while it is at the bottom dead center (that is, when this space is maximum), divided by the same volume, but when the piston is at the top dead center (when the volume of this space is minimum). What happens if we see in the technical characteristics of the engine that its compression ratio is 10, then this means nothing more than the fact that the maximum volume of the combustion chamber of one cylinder of such an engine is 10 times more than the minimum. Those. the fuel-air mixture in such a cylinder is compressed 10 times from the volume that enters it.

It turns out that there is a direct dependence of the compression in the cylinder on the degree of its compression, and this dependence is determined by a certain ratio. It is generally accepted that this coefficient is equal to 1.2-1.3 for gasoline 4-stroke engines. That is, if we know the compression ratio of our engine (and this information is presented in official documents for the car much more often than data on compression), then it will not be difficult for us to find out the engine compression.

Of course, in practice, these compressions will differ from those officially declared by the manufacturer, if only because this compression depends on the process of natural wear of the piston group, and the greater this wear, the less compression will be. But what is the line when the compression is so low that the engine components are considered overly worn? It is generally accepted that this criterion is equal to approximately 10-12% of the degree of compression declared by the manufacturer or obtained by calculations. That is, if, according to the documents, the compression rate should be 12 kg / cm 2, then it is easy to calculate that an engine with a compression of less than 10.56 to 10.8 kg / cm 2 is considered to be faulty.

Now let’s look at the brands and models of cars most popular among Russian motorists and find out what kind of compression should be in the cylinders of their engines.!

how to do a COMPRESSION test on a chainsaw or 2 cycle engine

Compression measurement results analysis

Depending on the results of the compression measurements, conclusions and recommendations for engine repair follow. The general and uniform drop in compression in all cylinders of the engine indicates a uniform natural wear of the parts of the cylinder-piston group and the engine as a whole.

If the compression of one cylinder is significantly different from the compressions in the others, then this unit should be given special attention. Cylinder leakage can be caused, for example, by a burnt-out valve, then disassembly, lapping or replacement of valves is required. Leakage can be caused by sagging piston rings. In these cases, the mechanics say “the rings are buried.” A drop in pressure can be caused by a burnt gasket between the cylinder block and the engine cylinder head. And in this case, not only a drop in compression is possible, but also the ingress of coolant into the lubrication system and vice versa, the ingress of oil into the cooling system.

What compression should be in the engine and how to check it?

Compression is the most important indicator of engine health. Each type of engine has its own compression: gasoline, diesel, turbocharged, three- or multi-cylinder And you need to monitor the compression. how?

What compression should be in the engine?

What are the compression and compression ratios for internal combustion engines? They are different. The compression ratio of a gasoline engine can range from 10: 1 to 13: 1, 14: 1, or even higher. The compression of a diesel engine is never lower than 20: 1. Textbooks on the theory of the car and all kinds of manuals define the compression ratio as: “… the ratio of the total volume of the cylinder to the volume of the combustion chamber. The compression ratio is determined using the following formula (V C) / C = CR, where V is the working volume of the cylinder and C is the volume of the combustion chamber “.

Compression calculation formulas do not exist, since this value is no longer calculated geometric, but absolute. This, as mentioned above, is pressure. Compression depends on many factors, the main of which is the quality of the tightness of mated pairs. cylinder-piston, cylinder-valves, cylinder-throttle valve, etc.

How to check compression without a compression gauge?

If there are complaints about the operation of the motor, suspicions of a loss of its power, and at the same time there is no compressometer at hand, then it is still possible to carry out a simple self-diagnosis. You will not get exact figures for the measurement of compression, but the general picture of the state of the motor will be visible to you.

See also  How To Start A Chainsaw Stihl 180 Video

The old chauffeur way is pretty simple.

Husqvarna 359 Chainsaw Low Compression

It is necessary to turn out each spark plug in turn, and instead of it, insert a banal paper gag into the candle hole. Exactly. paper. It is made from crumpled newspaper. not from a wet or oily rag-rag, but from a dry newspaper.

When you crank the crankshaft, the paper wad literally shoots up from the spark plug hole in the cylinder. over. with a very loud clap, but only if everything is in order with the compression of this cylinder. If the tightness is broken, if the valves (or valve) are burnt out, if the piston rings are stuck or the partitions on the piston collapsed, then the cotton will not be as expressive, or it will not be at all. It is this cylinder that needs “treatment”. That is, under repair.

What is engine compression and how to measure it?

Compression in cylinders. is the value of the maximum pressure in the cylinder, which is created at the top dead center (TDC) of the piston.

Measured in terms of pressure measures:

In today’s auto mechanics, it is customary to measure pressure in atmospheres and micropascals. MPa.

Compression is a physical quantity, it is pressure. It should not be confused with the compression ratio. this is a mathematical value, the ratio of the volume of the combustion chamber when the piston is at TDC to the total volume of the cylinder. Compression ratio, in contrast to compression, is measured in fractions of 1:12, 1:20, etc. Often the compression corresponds to the compression ratio, but, for example, in forced and turbocharged engines, these values ​​differ significantly.

Why measure engine compression? For diagnostics, it is an indirect indicator of problems in the engine and is measured by special devices, which are called by the minders. compression meters.

What are the compassometers?

Mechanical instruments for measuring compression, in turn, are clamping and screw-in. This is usually a specially calibrated pressure gauge with a rigid tip or flexible high pressure hose. Pressed against the candle hole or screwed into the candle thread instead of the candle.

Electronic testers are motor testers; they change not so much the pressure in the cylinder itself as fluctuations in the values ​​of the electric current of the starter at the time of idle cranking of the engine. Such an electronic device can simultaneously measure the compression of all cylinders without everting out the candles, and at the same time remove many other parameters.

Domestic mechanical compressometers are quite simple, while imported ones are real sets with sets of adapter adapters for measuring compression in an engine of any brand and modification of a car of any global manufacturer.

Stihl chainsaw low compression diagnoses and How To

Compression measurement in your car engine: how to do it?

The measurement of engine compression with a mechanical compressor is carried out according to the following algorithm. It is necessary to unscrew all the candles from the cylinders and turn the engine crankshaft idle, alternately measuring the compression in each cylinder:

At a professional car service, compression is measured with an open and closed throttle, and the difference in readings may indirectly indicate some defects in the engine. When the damper is closed, less air will flow into the cylinders, and the compression will be low. about 0.6-0.8 MPa. With an open damper, the picture will be different. the causes of engine defects can be determined from the attached table at the bottom of the article.

In any case, one should take into account not only the dynamics of the pressure rise, but also the maximum compression values. And most importantly, in any case, the results of measuring the compression in the cylinders are calculated, relative values, and one should rely on the difference in pressure in different cylinders. If in three cylinders the compression is, for example, 11-12 atm., And in the fourth 7-8 atm., Then the problem is concentrated in him. Here you should look for the reasons for the loss of tightness of the cylinder-piston group.

What to do if the engine compression is too low?

The main reason for the loss of compression is, of course, the loss of tightness. But where exactly did the depressurization occur? You can check this as follows.

50 ml of engine oil is poured into the “suspicious” cylinder and the compression is measured again. There are two possibilities. If the compression remains the same low, then the air comes out somewhere above, in the combustion chamber, and this can be either a leaky throttle valve, or a burnt-out valve, or a breakdown of the cylinder head gasket. And then all together. If the compression has risen significantly, then the cause is the “stuck” piston rings. And if the difference between the factory compression and the existing one exceeds at least 20-25%, then a bulkhead is inevitable. That is. overhaul of the engine.

How to increase the compression in the engine? Do Engine Compression Additives Help? Not always, but. they help. And before you start capital expenditure on expensive repairs, this opportunity is worth taking advantage of. But if the result turns out to be zero, then your car has a direct road to the service station.

Correct, and most importantly, preventive diagnostics of systems and engine components is the key to its trouble-free operation. Compression in the engine cylinders must be monitored periodically. In the same way. as well as for all other systems, units and assemblies of the engine and the entire car.

Only professionals will be able to carry out competent professional diagnostics, identify the reasons for the fall of the same compression in the engine, especially if you have not an ancient carburetor car, but a modern foreign car.

Use the form below to find specialized service stations nearby and sign up for a service at any time convenient for you.