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Check compression in the cylinders

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How to check the pressure in the cylinders of a car engine

Choosing a car, we pay attention to many of his characteristics, but primarily, we are interested in, of course, the power of the engine.

Особенно интересует мощность двигателя

Particularly interested in the power of the engine

If your car suddenly fell to the power of the engine or does the engine began to run with great difficulty, we will be required to undertake initial diagnosis of the car, and need a compression test of the motor vehicle. Anyone, without exception, the motorist will be able to check the pressure in the cylinder of the engine, that is, the check engine compression.

What is the engine compression?

Compression translates from Latin as compression. Motorists under compression understand the value that determines air pressure in the cylinders at the end point of the compression stroke. When checking the engine compression with a certain accuracy to know what problems exist in the operation of the engine without disassembling it.

Компрессия – давление в цилиндрах двигателя

The compression pressure in the cylinders of the engine

To check the compression for Amateur use there is a special device — compressometer. Modern compressometer equipped with everything necessary for the consumer, including adaptors (adapters) for different models, can be measured the compression in a diesel engine car.

Measurement of the compression of the engine in car repair is carried out using motortester or kompressorov, but we will not consider.

The reduced compression can be caused by a variety of reasons, including wear parts, piston group, malfunctions of parts of the timing, etc. the list can be very long. But the most important thing to know is that if you lower the pressure settings of the engine and the efficiency is much worse.

Ordinary motorists are unlikely to be understood by the figures, which are obtained when checking the compression in the cylinders of the engine.

For simplicity and convenience, there are specific guidelines to measure the engine compression. You must use the manual for the specific engine type.

Самостоятельное измерение компрессии двигателя

Self-measurement of engine compression

The overall average compression for a working petrol engine 9.5 – 10 ATM., the difference values in the cylinders should not exceed 0.5 – 1 ATM.

Factors affecting engine compression

The maximum pressure in the cylinder at the end of the compression stroke is determined by several factors:

  1. Throttle valve position. When the cover or closure significantly reduced the pressure in the cylinder.
  2. The degree of contamination of the air filter.
  3. Error installing camshaft timing, which allowed, for example, when mounting a drive chain or belt. This changes the moment of closing of the inlet valve, thereby shifting the beginning of compression in the cylinder at that side or the other.
  4. The clearances in the valve train. With a small gap in the actuator of the intake valve occurs later closing time and, consequently, decrease the compression. Also the small gaps increase valve overlap, that is, the crank angle at which the cylinder simultaneously open both valves. As a result, the compression also decreases.
  5. The temperature of the engine. The lower the temperature, the further cooled compressed in the cylinder of the air, which means more and its pressure.
  6. Air leakage. Air leaks can reduce the engine compression. They can be caused by worn and damaged parts, sealing the cavity of the combustion chamber.
  7. Oil. When applying oil to the combustion chamber through the valve guides, seals, turbocharger, piston rings and the crankcase ventilation system, the compression of the engine is significantly increased, as this causes the sealing action.
  8. Fuel. Upon admission of fuel into the cylinder in the form of drops compression, on the contrary, is reduced because it causes dilution and flushing of oil from the parts and reduces the sealing effect due to its low viscosity.
  9. Leaky check valve or hose compressometer.
  10. Speed of the crankshaft. The more will be the speed of the crankshaft, the higher the compression, as reduced leakage through leaks.

So, what is the compression, of course. Now let’s talk about how to measure the engine compression yourself?

First of all, I must say that the compression test should be carried out in several cases. First, if decreased engine power, and secondly, the overhaul of the cylinder block or cylinder head repair. In the first case, check the compression in the cylinders required, in the second it is done for control.

To check the engine compression you will need compressometer. Modern compressometer equipped with adapters (adaptors) that allows you to check compression engines in all brands of cars.

Прилагаемые насадки могут быть использованы на любом типе двигателя

The attached nozzles can be used on any type of engine

If you don’t have their own stations, the motortester and compressori do not concern yourself, since these appliances are intended for commercial use them in the service station.

In addition compressometer, you will need the manual for your engine type, which are standard options the amount of compression.

Check the compression and the procedure for cylinders of any car is almost the same. Here are the basic rules that you need to know to measure the engine compression yourself:

  • Rule one: check compression in the cylinders, you need warm engine.
  • Rule two: you must first turn off the supply of fuel (i.e. fuel pump, injectors).
  • Rule three: you must Unscrew all of the candles. Not to do so selectively, as do some foolish master.
  • Rule four: the battery needs to be fully charged and the starter is healthy.
  • Rule five: check compression in the cylinders must be executed with open or closed throttle. For each method will be your results engine. In the case of an open valve, you can quickly identify problems such as burnout of the piston, the deformity of the valves, coking of the rings and the scratches on the surface of the cylinder. In the case of a closed valve changing the value of compression would indicate such faults as leakage due to burnout cylinder head gaskets or cracks in the combustion chamber, as well as freezing of the valve.

Замер компрессии позволяет определить наличие поломок и дефектов

A compression test to determine the presence of failures and defects

  • Rule six: the pressure in the cylinder of the engine is checked in turn. Using the starter rotates the crankshaft as long as you do not stop to increase the pressure, then recordable indications. It is then reset and so on with all the other cylinders.

The question arises, what to do after measuring the compression in the cylinders? First of all, you need to understand that the results are relative. That is, should be interested not so much the absolute amount of compression, how much the difference of the readings for different cylinders. Thus, it is possible to know which cylinder is the problem.

Video — definition of compression in the engine cylinders


If the pressure in one of cylinders of the engine is lowered, then this suggests that, most likely, occurred the burning of piston rings. This can also happen when the loose fit of the valves in the seats. Anyway, when identifying reduce the compression of the engine, you need to roll up our sleeves and begin to repair the engine.

We wish you good luck, let your engine will always be normal!