How to check the compression of the engine without devices: available ways

As you know, the compression indicator in the engine allows to receive certain information on a condition of the motor without dismantling and defecting of the power unit. Compression measurement is a diagnostic operation, which conditionally allows to estimate "tightness" of the cylinder and efficiency of compression of mix.

Next we'll talk about that, what methods allow to measure compression on cylinders, which faults indicate a decrease in compression, as well as how to determine the compression in the engine without the device, that is, perform the necessary diagnostics in the field if necessary.

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

As for the compression itself, without going into details, this is the pressure in the cylinder. The specified pressure directly depends on that, what is the degree of compression in a motor. To measure 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, reduced compression leads to, that the fuel-air mixture in the cylinder will be compressed insufficiently for normal charge combustion. As a result, the power unit may start at too high a force, work erratically, triple (one or more cylinders do not work or work intermittently). There is also a decrease in power, fuel consumption increases, etc..

Extraneous noises and knocks may occur in the engine at the same time, power unit in some cases works quite "roughly". Quite obviously, that the problem needs to be identified as soon as possible, so that the already existing problems of the power unit do not grow into a whole set of more serious problems.

Compression measurement: without a compressor or with the help of special equipment

so, in practice, only two methods are actively used, which allow you to make compression measurements:

• using a compressor;
• measured compression by hand;

Naturally, the presence of the device allows you to get the most accurate readings, however, in emergencies or to obtain approximate evaluation results, the decision to measure the compression manually is also practiced..

Let's note at once, to measure compression without instruments, some skills and knowledge will be required, the operation is not very difficult, and even for novice motorists.

1. First you need to unscrew the spark plugs, leaving only the spark plug in the first cylinder.
2. Then the crankshaft should be turned so, so that the piston in the first cylinder was at the end of the compression stroke.
3. To pinpoint, that the piston is in the correct position, you need to check the labels.
4. Next you need to remember something, with what effort the crankshaft turned by hand.
5. After that the candle is screwed in the second cylinder and so on.

The main task is to identify the problem cylinder, when the crankshaft rotated most easily after screwing in the spark plug (with the least effort). In other words, if the compression is reduced in one cylinder, then the effort, to be applied for scrolling cloned, will be less compared to checking the compression of other cylinders.

Note, that although the method is quite primitive, however in some cases even it allows to receive the general idea and to find out a problem in this or that cylinder of the engine.. More accurate measurements can only be made with a compressor.

1. First of all, you need to study the technical documentation for a specific type of engine installed on the machine.
2. Determining the specific value of compression for the engine, it is necessary to start the motor and to warm up it before an exit to working temperature (the cooling fan is switched on).
3. Then the spark plugs are carefully unscrewed. Next you need to invite an assistant, which will squeeze the accelerator pedal (an important condition for compression measurements) and scroll the engine starter.
4. If we talk about the device, the compressor has a special tip, which is tightly inserted into the hole of the candle.
5. After that, the engine scrolls the starter close 3-4 sec. It is also important to consider, that compression should be measured provided that, that the battery is charged and the starter itself is fully functional. The point is, that insufficient crankshaft speed can lead to a significant decrease in performance, however, this will not mean, that the compression in the engine dropped so much.
6. Then, when the testimony was obtained, they need to be compared with the nominal ones for a specific engine.

We will add, that the difference in compression readings for all cylinders (data scatter) should not be more 1/10 from the maximum value. This means, what if in some cylinder the compression fell on 15-20% compared to others, then there is a high probability, that worn piston and piston rings, there was damage to the timing valves, etc..

It is also important to understand, that continued to operate the engine, in which the compression is reduced in one or more cylinders, not recommended. The point is, that the parts in this cylinder will wear out even more, the engine itself will vibrate more and run erratically, excess unburned fuel flows into the oil pan, which will cause oil thinning, thereby increase the overall wear of the internal combustion engine, etc..

Low compression and how to understand, what is the problem: CPG, ring or valve

As already mentioned, decreased compression can occur for a variety of reasons. At the same time quite often this leads to occurrence, wear or destruction of piston rings. To check the rings on the spot without disassembling the engine, you can use the available method of testing with engine oil. All you need to have a candle key on hand, a little oil and a syringe.

• After, as the problem cylinder was detected and compression readings were recorded, through the candle hole you need to pour the syringe close 20-30 ml. pure oil.
• Then you need to close the hole and scroll the engine starter. This is necessary for that, so that the oil spreads on the cylinder.
• Next, re-measurement of compression in this cylinder.

In that case, if the compression is clearly increased or even close to normal, then it is likely, that the following elements of the CHP are worn out: pistons, rings or the walls of the cylinders. In this case, the oil "seal" the existing defects, allowing to achieve the necessary compression of the mixture in the cylinder.
We also recommend reading the article about it, why the compression is increased in the engine and what problems lead to it. You will learn from this article, why increasing compression is bad for the motor, as well as the consequences for the internal combustion engine, if the compression in the cylinders is above normal.

If the compression ratio after pouring the oil increases slightly, then problems with valves are quite possible (example, burnout of the valve, etc.). The piston rings can also be severely damaged, as well as punched cylinder head gasket.

The complete absence of any changes means, that the tightness of the combustion chamber is violated due to any problems with the valve mechanism. It is possible, that the valve is loose to the seats, that is, they need to be regulated, grind, etc.. Also, cracks and breakdowns in the BC or cylinder head should not be excluded.

As a result

As you can see, the need to measure compression can arise for various reasons. Most often, this procedure is used in the general diagnosis of ICE. Measurements are also made after that, as the engine was assembled after repair (as capital, and sorting). This is necessary to identify possible defects after assembly.

We also recommend reading the article about it, why there is low compression in the diesel engine and how it affects the operation of the diesel engine. In this article you will learn about the reasons for reducing compression in a diesel engine, what symptoms indicate this, etc..
We will note still, that although checking the compression of the engine without a compressor in some cases allows you to localize the problem, more detailed information cannot be obtained. It is worth adding, that a simple compressor is quite affordable (usually, the cost is about 15-20 u.o.).

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