How to check the compression on the trimmer

Table of Contents:

Measurement of compression in cylinders of a carburetor engine

The procedure and recommendations for measuring compression in cylinders given in the article are applicable for gasoline carburetor engines of passenger cars VAZ. 2108, 21081, 21083, 2109, 21091, 21099, 2101, 2106, 2105, 2107, 21021, 210213, 1111 and a number of similar (Moskvich, Izh, Volga.). Compression measurement on injection engines has a number of features and will be discussed in a separate article.

Before tuning and adjusting the carburetor of your car, you should take into account the general condition of the engine, since the symptoms of a number of its malfunctions can be mistakenly considered symptoms of carburetor malfunctions. For example, an unstable idle or difficult start may indicate not only problems in the idle system or the carburetor starting system, but also that one of the valves in the engine is burnt out, the head gasket is broken, the piston rings are worn out or stuck, etc. After measuring the compression, we will more or less accurately determine the condition of the engine and identify possible malfunctions in its operation. After eliminating them, you can safely adjust the carburetor.

How to check compression in engines on a VAZ 2101

How to check engine compression on a VAZ?

To carry out the check, as we have already said, it will be needed: A compressor, as well as additional tools, thanks to which it will be possible to unscrew the spark plugs, where the compressor will be inserted, in eight-valve cars such tools include a spark plug wrench, in shesnary cars it will be you need a small spanner key and also a candle key, but there is a candle in the shesnary, take this into account!


When to check compression?
If you have a compression meter, then at least measure it every day, but still, if you are realistic, you often do not need to do this, because when checking, the battery is set (since it turns the engine idle) in the car, in general, the compression MUST be measured in the following cases:

When buying a car, in this way you will find out in what state the engine is, and you will also know you need to do it (Capital) or it will live for some time.

And also after more mileage of the car (When the engine is already driving badly), exactly after what mileage we will not indicate, because there are people who manage to screw up a new engine and then shout why the car does not drive, why is it so badly done, and it all depends on you, dear motorists, how you will operate the car, so he will answer you.

It is not easy to understand that compression has disappeared in the engines (Without a device), if it has completely fallen, then you will notice it immediately, we do not deny it, but the symptoms will be as follows, the thrust will drop, in addition, the engine will triple only on three cylinders), it will have vibration, the engine will sausage back and forth (If we take the classic engines, then they are sausage even from the factory itself, but the shaking there should be very small, but it will be, if the engine is to the left and to the right throws only in this way, then this already says a lot, first of all about the fact that the engine runs on three cylinders, and it can work on three if the ignition disappears on one of the cylinders, as well as if the compression in the cylinder disappears for so on), but but if the compression has not disappeared much, then it will not be easy to understand (Without a device), but remember once and for all, such an engine must be repaired as soon as possible, if you pull it, then it will only be replaced!

Measurement of compression in cylinders of a carburetor engine

The assistant, sitting in the car, presses all the way on the gas pedal and turns the key in the ignition lock, starts the starter for 3-5 seconds.

We observe the readings of the compressometer, record the dynamics of their growth and the maximum value. After fixing, release the pressure in the device by pressing the reset button.

We repeat the operation for each cylinder, write down or remember the measured readings.

Preparatory work

Warm up the engine to operating temperature (80-90º).

We remove the fuel supply hose from the fuel pump.

We unscrew all the spark plugs, having previously cleaned their wells from dirt and debris.

We take out the central armored wire from the distributor cover, insert the spark plug into it and put it on the engine.

We screw the tip of the compressometer into the hole of the first cylinder, or press it firmly against this hole.

Measurement of compression in cylinders of a carburetor engine

Compressor readings analysis

For extended analysis of the compressor readings after the compression measurement, see “Compressor Readings Analysis and Interpretation”. After the analysis, you can independently, with a high degree of accuracy, determine the malfunction of the rings, pistons, cylinders and valves of the engine.

Notes and additions

Factors Affecting Compression Measurement Uncertainty

Compressor readings will be lower if:

Compressor readings will be higher if:

Determination of the causes of reduced compression in the engine cylinders using compressed air

Determine the compression stroke in the desired cylinder. Insert a thin long screwdriver (a wooden stick, a piece of wire.) into the spark plug hole of the desired cylinder and hold it with your hand, resting on the piston bottom. We turn the crankshaft by the ratchet (on engines 2101-2107) or with a large slotted screwdriver by the flywheel teeth in the hatch on the clutch housing (2108.). When the piston moves up (compression stroke), the screwdriver will come out of the spark plug hole, supported from below by the piston. It is necessary to catch the moment when it stops moving up and starts moving down following the outgoing piston (intake stroke). This moment will be the top dead center when the piston moves, the end of the compression stroke.

How to compression test a Stihl FS90R Trimmer Weedeater

We insert the compressor hose into the spark plug hole and supply compressed air to the cylinder under a pressure of 2-3 atmospheres. According to where it will come from, we determine the malfunction.

From the adjacent spark plug hole or into the expansion tank (drilling). the block head gasket is burnt out.

From the carburetor. the inlet valve is burnt out or the valves are not adjusted.

From the muffler. the exhaust valve is burnt out or the valves are also not adjusted.

From the breather. the rings are worn out, the pistons are burnt out.

Determining the causes of reduced compression with engine oil

Pour 10 cubes of engine oil into the cylinder and re-measure the compression. Compressor readings have increased. the rings are faulty or stuck, the cylinder-piston group is worn out, remained the same. the valve or the head gasket is burnt out.

De-carbonization (elimination of sticking) of piston rings

Pour 10 cc / cm of a mixture of kerosene (50%), acetone (25%), engine oil (25%) into the spark plug hole of each cylinder of a heated engine using a medical syringe or a rubber bulb.

Let it stand for 3-4 hours, if desired and if there is time, you can leave it overnight.

After this time, turn it with a starter for 10-15 seconds with the candles turned out.

Drain the old oil, replace the oil filter and refill with a new one.

Thus, after making sure that the car’s engine is in good working order, or having identified a malfunction and eliminating it, you can thoroughly start adjusting and tuning your carburetor, excluding, as a result of the measurement, other causes of the malfunction related to the engine.

There is also a lot of interesting and useful information on this topic on the site

TWOKARBURATORS VK. information in our group

Analyzing data

In order to understand how good the engine gave you, you need to have a “Operator’s Manual” for your model and type of car. There should be described the standard values ​​for this particular type of engine. Often, the normal compression of the VAZ 2107-2170 model engine is from 9.5 to 10 atmospheres. In this case, a small scatter in the values ​​is allowed. up to 1 atmosphere. If the compression in your engine is approximately 8.5-11 atmospheres, this is an excellent indicator. But again, in order to make a more accurate calculation, you need to have manual and documentation specifically for this engine model.

But if the values ​​you received are below 8.5 atmospheres, then there are malfunctions in the engine that you must certainly eliminate. In order to identify them, you will need 10 milliliters of engine oil. We pour it into a cylinder and repeat the measurement.

If the data obtained significantly increased and even became an order of magnitude higher than the norm on subsequent measurements in the 2nd, 3rd and 4th cylinders, most likely you have a malfunction in the piston group. This could be ring stuck or worn. To eliminate this malfunction, it is necessary to completely de-carbonize the engine. Well, if the pressure level in the cylinders remains the same, then the problem is hidden in the valves, namely. in their poor fit. It also happens that the cause of reduced compression is valve burnout. Most often this happens due to cracks in the piston or a badly worn cylinder head gasket. This completes the engine compression test.

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What else can affect the compression of the internal combustion engine?

In general, there are a lot of reasons for changing the pressure in the cylinders. Among them, the following points should be highlighted:

  • Throttle position.
  • Incorrect valve drive clearance. It should be noted here that a small clearance can lead to a later closing, as a result of which the pressure in the cylinders decreases significantly. It can also change the angle of rotation of the crankshaft, as a result of which the compression will also significantly decrease.
  • Motor temperature. The operation of many elements of the engine depends on this parameter, in particular, the same valves. The lower the temperature, the smaller the gap. Accordingly, the pressure in the cylinders also decreases.
  • Various leaks in parts that seal the cavity of the combustion chamber.

Under what operating conditions will the engine be ideal for compression? The likelihood of air leakage through various holes will be minimal only if:

  • The cylinder will have a perfectly round shape.
  • Piston rings fit as tightly as possible to each other.
  • There are no longitudinal marks on the working surface of the cylinder.
  • The size of the gap in the locks of the rings is close to zero.
  • Valve s are as close to the seats as possible.

Why does this value decrease over time?

The reason for the decrease in pressure in the cylinders of the engine may be a malfunction of the elements of the gas distribution mechanism. But most often this happens due to the natural wear and tear of the mechanisms of the piston group. But be that as it may, lowering the pressure significantly affects the engine power and the total fuel consumption.

How is engine compression measured??

There is a special device for this. It is called a compressometer. At the moment, almost all of its models are equipped with special adapters for different engine models. The compressor is most often used at home, while professional services use more advanced devices for this. compressographs and motor testers.

Preparing the engine for measurements

Before proceeding with the measurement of compression, it is necessary to warm up the engine to operating temperature (at least 80 degrees Celsius). Also check the battery charge before use. If it is discharged, be sure to charge it before diagnostics. The serviceability of the starter also plays a special role in measuring the compression. When he turns the engine at a frequency of less than 200 rpm, such a car diagnostics will be simply useless due to the large difference in readings. If everything is fine with you, you can safely get to work.

What malfunctions can be detected using a compressometer?

Using this device at home, you can independently determine a number of malfunctions of the internal combustion engine. For example, if the compression does not increase, this may indicate that damage has formed in the valve seats, through which air escapes. If, on the scale, there is a rapid increase in this value (for example, at the 1st compression stroke, the pressure level is equal to three atmospheres, and then it increases to eight), this indicates wear of the piston grooves, rings or cylinder walls. When the damper is in the open position and at the same time there is a change in pressure parameters, it is most likely that there are scuffs on the surface of the cylinders, or the valves in the engine are deformed.

How to check engine compression? Car diagnostics

The serviceability of all components and assemblies is the guarantee of the smooth operation of any car. But if he suddenly began to lose power, or does not even start “hot” at all, then he should be taken to the internal combustion engine diagnostics. During this test, using special equipment, the pressure in the engine cylinders is measured. This process is called compression testing. Of course, it is not always possible to contact a professional in a car service. Therefore, today we will look at how to check the compression in the engine on our own.


So, how to check the compression in the engine yourself? First, we need to unscrew all the candle wires, then take out all the candles in turn. over, they should be laid out in such a sequence so that you can then screw each part into its place. Many motorists ask themselves the question: “Why is it necessary to unscrew all the candles?” The answer to this question is very simple. The fact is that checking the compression with the plugs screwed in will not give an accurate result. All values ​​will be approximate only, inaccurate or with large fluctuations. Therefore, in no case should you unscrew only one spark plug in the engine.

But back to work. How is engine compression measured further? After the candles, for safety reasons, we disconnect all low-voltage wires from the coils. Further, if you have a carburetor engine and a mechanical pump, remove the fuel hose. This will shut off the fuel supply to the cylinder. If you have an injector and an electric fuel pump, pull out the relay of the device or remove the power wires from all injectors. After these manipulations, you can start measuring.

How to use a compressometer? First you need to install its end in the spark plug hole, then press the gas pedal (until the throttle valve opens) and start the starter so that it turns the engine. We do this until the data on the scale of the compressor stops growing. After that, we write the obtained data into a notebook and be sure to number the cylinder, the pressure in which we have just measured. After that, we reset the indicators on the compressor and go to the next cylinder. We diagnose it in the same way.

After the pressure on all cylinders has been measured, we collect all the elements in reverse order and proceed to the analysis of the data obtained.

Compression check procedure

Disconnect the high pressure pump fuel cut-off valve connectors.

Disconnect high pressure pump dispenser.

Remove one of the glow plugs.

Connect a compressor or a compressor to the glow plug flange.

Measure the compression with the starter on. The measurement is considered complete when the compression gauge readings stop increasing.

Repeat the measurement, placing the device in the place of the next candle. Record the results of each test.

Reinstall the candles.

Reconnect the fuel cutoff valve connectors and turn on the high pressure pump dispenser.

  • How to check compression in diesel engines
  • How to check compression
  • How to measure compression

Compression is the pressure that is created in the engine cylinder while it is being rotated by the starter motor, when the fuel supply system has not yet come into operation. Compression is one of the most important indicators of engine health. Compression ratings for various engines under normal atmospheric conditions are 28-40 atmospheres.

Checking the compression of a diesel engine involves diagnostics of the cylinder-piston group, which is carried out with a special device. a compression meter or a compressor. The device includes a shut-off valve that prevents pressure release when cranking the crankshaft.

The difference between the two devices is the different way of displaying information. The dial of the dial gauge serves for these purposes in the compressometer, and the compressor allows you to display the data on a computer monitor or print a report on the test results on paper.

How to check compression in diesel engines

Test conditions

The nominal compression value and the value of the maximum tolerance can be found in the operational documentation for the car.

Compression testing should be performed at a crankshaft speed of 200-250 rpm. The condition of the air filters is also a prerequisite for the accuracy of the measured readings. Clogged filter may distort compression readings.

Compression is measured under those temperature conditions in which the actual engine start usually takes place. There is a direct relationship between ambient temperature and the minimum compression at which the engine can start. This performance for a specific engine can be obtained from a series of tests carried out in a workshop environment.

How to increase engine compression

When the car is in operation for too long, there are problems with engine compression. Most often, this is found in VAZ cars, the engine volume of which does not exceed 1300 cubic centimeters. Fortunately, in most cases, even a beginner is quite capable of restoring past performance.

However, there are a number of challenges you will have to face when restoring engine compression. The first step is to determine what exactly is causing the compression problem. You also need to take care of a set of tools in advance that will help you recover the malfunction.

We restore compression without overhaul

In most cases, to restore the normal functioning of the part, it is not required to carry out major disassembly and repair. There are a number of substances that help to carry out high-quality recovery with minimal expenditure of strength and energy.

Recovery with special additives

I think that every driver has heard more than once about the miraculous effect of automotive additives that help restore its former power and reduce oil consumption. Also, everyone has heard that these funds are absolutely ineffective. In reality, the truth is somewhere in between.

Video. restoration of compression:

For the sake of fairness, it should be said that in the 90s, at the peak of the popularity of additives, a lot of low-quality fakes appeared on the market that did not help restore engine compression. But it also cannot be denied that the leading manufacturers of fuel and lubricants still produce additives and position them as a means of restoring key vehicle components.

High-quality additives ensure the restoration of worn metal areas on engine parts, thereby increasing compression. The thickness of the protective layer is minimal, but it is more than enough to patch up the areas worn out by time. Of course, this greatly contributes to the restoration of compression.

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Diagnosing insufficient compression in the engine

Before proceeding with the recovery, it is necessary to determine exactly what the problems are with the compression. There are a number of factors that indicate precisely that engine malfunctions are associated with this defect:

  • decrease in power;
  • increased consumption of oil and gasoline;
  • thick acrid smoke from the exhaust pipe.

Compression Test on a 2 Stroke Trimmer

If, while driving, you find at least one of the above symptoms, then this will be an important signal of a malfunction in the engine and the car as a whole.

check, compression

Loss of tightness between pistons and cylinders can be caused by wear of the piston rings. It is they who provide the tightness between these two engine components.

When the rings between the pistons and cylinders become unusable, oil enters the combustion chamber. Because of this, black smoke comes out of the chimney, power decreases and the consumption of fuel and lubricants increases. over, the exhaust gases enter the crankcase.

Compression problems are very common after repairs. For example, when the assembly is done incorrectly, the engine power drops significantly. A number of other more serious problems can also be observed.

In this case, there is no compression at all. This is because the valve stem is bent. This is due to the fact that the part does not fit tightly into the groove. Restoring such a malfunction is very troublesome.

Diagnostics using special devices

The symptoms described above can only indicate insufficient compression in the engine. In order to carry out recovery, you will need to accurately determine the cause of the malfunction. and this requires special equipment:

  • compressometer;
  • a set of special keys;
  • some engine oil;
  • syringe.

The first thing you will need to do to get reliable data is to set the clearances correctly. Otherwise, all the information you have gathered to restore compression inside the engine will be useless.

The compressor provides the most accurate data. Although it is possible to carry out all measurements manually. However, in this case, the accuracy of the collected data will be in doubt.

In order to determine what exactly caused the compression problems in the engine, you need to carry out the following manipulations:

  • leave only one candle in the nest. Unscrew the rest;
  • the crankshaft must be cranked before the end of the compression stroke;
  • the candles must be unscrewed in turn, while gradually rotating the crankshaft.

As a result of these simple manipulations, you can understand what exactly causes a violation of compression in the engine and restore.

Start the car before taking readings from the device. As soon as the temperature in the engine reaches 85 degrees. turn off. After that, you will need to unscrew the candles and open the throttle.

To get accurate data, one person must be at the engine and the other at the wheel. The task of the assistant will be to turn on the starter, simultaneously pressing the gas pedal to the floor.

You can turn the crankshaft only when the starter is on. You will have about two seconds to get information that will help restore compression in the engine. To determine the problem area, you will need several measurements.

When measuring compression in an engine, you must take into account that there will be an ideal indicator for each car model. Usually, this data should be provided by the manufacturer in the official documentation or on its website.

It is worth recognizing that the wear and tear of a car is a natural fact that cannot be avoided. Therefore, after your vehicle has traveled a sufficient number of kilometers, check the engine for compression. In addition, it is always easier to repair a small malfunction than a large one.

Removing carbon deposits

You can use an old proven method that has been used by drivers for many years to loosen o-rings that have carbon deposits on them.

The fact is that due to low-quality fuel, microparticles remain on the internal components of the car. They significantly interfere with the restoration of normal compression.

It must be poured through the engine plug socket. One hundred grams is enough to carry out the recovery. After that, just leave the engine on for half an hour. Clean engine oil will remove fumes. Usually, after this procedure, the restoration of compression is observed almost instantly. Rings cleaned from burning will regularly perform their task.

The video shows the restoration of compression after flushing the engine:

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 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. Diesel engine compression 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 the coupled 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 compression measurement, but the general picture of the state of the motor will be visible to you.

The old chauffeur way is pretty simple.

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.

check, compression

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 septa 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. compressometers.

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.

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.

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If the compression of one cylinder differs significantly 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 the compression must be monitored. how?

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 “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.

Compression measurement: without a compression gauge or using special equipment

So, in practice, only two methods are actively used that allow you to measure compression:

  • using a compressometer;
  • measurement of compression by hand;

Naturally, the presence of the device allows you to get the most accurate readings, but in emergency cases or to obtain approximate estimated results, it is also practiced to measure the compression manually.

check, compression

Immediately, we note that in order to measure compression without devices, certain skills and knowledge will be required, while the operation does not present any great difficulties, and even for novice motorists.

  • First you need to unscrew the spark plugs, leaving only the spark plug in the first cylinder.
  • Then the crankshaft must be cranked so that the piston in the first cylinder is at the end of the compression stroke.
  • To accurately determine that the piston is in the correct position, you need to check the marks.
  • Next, you should approximately remember with what effort the crankshaft was turned by hand.
  • After that, the candle is screwed into the second cylinder, and so on.

Note that although the method is quite primitive, in some cases even it allows you to get a general idea and identify a problem in a particular cylinder of the engine. accurate measurements can only be carried out using a compressometer.

  • First of all, you need to study the technical documentation in relation to the specific type of ICE installed on the car.
  • Having determined the specific compression value for the engine, it is necessary to start the engine and warm it up until it reaches the operating temperature (the cooling fan turns on).
  • Then the spark plugs are carefully unscrewed. Next, you need to invite an assistant who will depress the gas pedal (an important condition when measuring compression) and crank the engine with a starter.
  • If we talk about the device, the compressor has a special tip that fits tightly into the spark plug hole.
  • After that, the engine is cranked by the starter for about 3-4 seconds. It is also important to take into account that the compression should be measured provided that the battery is charged and the starter itself is fully operational. The fact is that insufficient crankshaft speed can lead to a noticeable decrease in performance, but this will not mean that the compression in the engine has dropped so much.
  • Then, when the readings have been obtained, they need to be compared with the nominal values ​​for the particular engine.

It is also important to understand that it is not recommended to continue to operate an engine in which the compression is reduced in one or more cylinders for a long time. The fact is that the parts in this cylinder will wear out even more, the engine itself will vibrate more and work unstably, excess unburned fuel will drain into the oil pan, which will cause oil dilution, thereby increasing the overall wear of the internal combustion engine, etc.

Checking engine compression without a compression gauge

As you know, the compression ratio in the engine allows you to obtain certain information about the condition of the engine without disassembling and troubleshooting the power unit. Compression measurement is a diagnostic operation that conditionally allows you to assess the “tightness” of the cylinder and the efficiency of the mixture compression.

Next, we will talk about what methods allow you to measure the compression on the cylinders, which malfunctions are indicated by a decrease in compression, and also how to determine the compression in the engine without a device, that is, to perform the necessary diagnostics in the field if necessary.

Low compression and how to understand what the problem is: CPG, rings or valves

As already mentioned, compression reduction can occur for various reasons. In this case, quite often this leads to the occurrence, wear or destruction of the piston rings. To check the rings in place without disassembling the engine, you can use the available check method using engine oil. You only need to have a spark plug wrench, some oil and a syringe on hand.

  • After the problem cylinder has been identified and the compression readings are recorded, about 20-30 ml must be poured through the plug hole with a syringe. pure oil.
  • Then the hole must be closed and the engine cranked with a starter. This is necessary in order for the lubricant to spread through the cylinder.
  • Next, the compression in this cylinder is re-measured.

If the compression index after oil filling increases slightly, then problems with the valves are quite possible (for example, valve burnout, etc.). Also, the piston rings can be severely damaged, as well as the cylinder head gasket is punctured.

The complete absence of any changes means that the tightness of the combustion chamber is broken due to any problems with the valve mechanism. It is possible that the valves do not fit tightly to the seats, that is, they need to be adjusted, lapped, etc. Also, cracks and breakdowns in the BC or cylinder head should not be ruled out.

Engine compression: what it is and what deviations from the norm lead to

As for the compression itself, without going into details, it is the pressure in the cylinder. The specified pressure directly depends on the compression ratio in a particular engine. To measure the compression, the maximum air pressure at the end of the compression stroke is measured.

If we talk about the problems of the internal combustion engine, a decrease in compression leads to the fact that the fuel-air mixture in the cylinder will not be compressed enough for normal combustion of the charge. As a result, the power unit can start up with great difficulty, work unstable, triple (one or several cylinders do not work or work intermittently). There is also a decrease in power, an increase in fuel consumption, etc.

What is the bottom line

As you can see, the need to measure the compression can arise for various reasons. Often this procedure is used as part of a general diagnosis of the state of the internal combustion engine. Also, measurements are taken after the engine has been assembled after repair (both overhaul and bulkhead). This is necessary to identify possible defects after assembly.

Also, the device, if necessary, can be made independently using a pressure gauge, tubes and various adapters. For this reason (especially for owners of cars with a solid mileage) it is recommended to have a separate ready-made device for measurements in the car.

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