Compression is ... Compression of the engine - what is it?

Compression is the determining factor of engine longevity. It is on this indicator depends on the degree of wear of various parts of the motor. Therefore, motorists try to support it in various ways. Compression of the engine - what is it and how is it measured? In today's article, we will try to describe this phenomenon in detail, and also learn how to measure it on our own.

Characteristic

Compression is the maximum degree of air pressure in the combustion chamber, which is achieved when the piston is in the TDC during the compression stroke. The magnitude of this characteristic determines the serviceability of the motor, as well as the durability of the operation of all its mechanisms. In simple words, compression is an indicator of the viability of the engine, that is, the main factor in the state of its health.

What does it affect?

Many processes depend on the level of this value, namely:

1. Completeness of combustion of fuel in the chamber.
2. Oil consumption.
3. Serviceability of the cylinders. A low compression class increases the risk of engine damage.
4. Easy to start the engine. If the value of the compression ratio is lower than normal, it is very difficult to drive such a motor, especially "cold".
5. Power of the power unit. Over time, it can fall. The smaller the compression class, the lower the car's power. Accordingly, this implies the weak characteristics of the dynamics of motion and acceleration.

The reasons for the reduction of compression

One of the main reasons for low compression is engine overheating. With frequent boiling of the engine in the cylinders are formed scuffing. They can also appear on the pistons. The latter as a result melt or burn out. Low compression (VAZ of the "tenth" family including) indicates the wear of the partitions of the rings. As a result of all these signs, the power is noticeably lost, while fuel consumption is increasing .

Also one of the reasons for the drop in compression is a malfunction in the timing system. In this case, there is a high risk of burnout of the valves. Such a detail is no longer subject to recovery. Burnt out valves should be changed immediately, otherwise the power drop and increased fuel consumption will not stop.

By the way, one of the reasons for the burnout of the valves, and therefore the drop in compression, is their improper adjustment. If there is no necessary thermal gap between them, we can talk about serious malfunctions in the gas distribution system. In this case, the valves will not close completely. But a large gap is also fraught with its consequences. For example, this may cause insufficient opening of the valves. Because of this, less air enters the cylinder. As a result - knocking under the valve cover.

The compression also falls strongly due to the burnout of the cylinder head gasket. In this situation, the exhaust gases will not flow through the muffler and exhaust manifold, but directly into the oil line or into the engine cooling system.

What else can indicate a low compression ratio? The main reason for the loss of compression is the wear of the piston rings and the development of cylinders on the walls. Here the problem is further accompanied by an increased consumption of oil and gasoline.

Ironically, even an air filter can cause low compression. The thing is that the clogged element does not allow air to get into the cylinders. This results in a very lean mixture, practically without oxygen. In some modes of operation this is normal, but when the fuel mixes in such proportions all the time, there is reason to sound an alarm.

The last reason for the reduction in the compression ratio is the crack in the head of the block. Often it happens due to engine overheating. But if you think that because of the low compression ratio the stockings are torn on the bridges, compression is not to blame. Most likely, there was an overload in the rear of the car, no more.

What is the normal compression of the engine?

What is it - the phenomenon of compression - we already found out. Now a little about the numbers. But first you need to note that this indicator is installed on each engine separately, by its manufacturing plant. The exact value of the compression is indicated in the instruction manual of your vehicle. For gasoline engines, this indicator should correspond to the order of 9.5-10.5 atmospheres. Compression VAZ'ov "tenth" family is slightly higher - 11 atm. On diesel engines, the compression ratio is between 28 and 32 atmospheres. In this case, the spread between the cylinders should not exceed more than 0.5-1 atm for petrol and 2.5-3 atm for diesel power plants. Such different compression classes of stockings are the result of different types of fuel ignition. If the gasoline engine ignites it with a spark, then the diesel engines are compressed. Hence, such a different compression. This makes the diesel engines more durable and wear-resistant. Practice has shown that the higher the factory compression ratio, the more powerful and economical the engine is.

Experts say that the value of compression may differ, despite the stable technical condition of ICE. This may occur due to the difference in conditions in which measurements were made.

There are several factors that can affect the result of compression measurement:

1. The volume of air that enters the cylinders.
2. Engine temperature.
3. Crankshaft speed.

It should also be noted that a viscous oil that has settled on the walls of the cylinder also contributes to an increase in the value of the compression ratio. This phenomenon is observed due to the sealing of the gap between the conjugate elements. Conversely, the compression is reduced due to excess fuel, which enters the combustion chamber.

Do not panic and wonder if the mileage of the car is 200-250 thousand kilometers, and the readings are very large (for example, 10 atmospheres for a gasoline engine). The reason for this can be the accumulation of a thick layer of carbon on the elements of the combustion chamber. As these deposits accumulate, the volume of the combustion chamber itself decreases, which leads to such questionable results.

When does the compression level increase?

In addition to the above factors, this indicator can be increased because of:

• The presence of oil in the combustion chamber.
• High engine temperature.
• Fully open throttle.

Experienced motorists say that when measuring the compression, it is necessary to pay attention only to three points: engine temperature, fuel and throttle position.

How often should I take measurements?

Drivers say that you need to measure the compression ratio every 10-40 thousand kilometers and record all the values in a notebook. Thus, you will constantly know in what state your engine is at the moment. This will avoid such troubles as overheating of the engine, burnout of valves, pistons and their coking.

In what conditions should you make measurements?

It is very important to observe the rules for measuring this indicator, because the accuracy of the measurement depends on this, and consequently the further life of the "heart" of your iron horse. So, when working with a compressometer it is important to pay attention to the following points:

• Engine temperature. The motor must be warm before the measurement, and its temperature should fluctuate within 40-60 degrees Celsius.
• The fuel supply must be switched off.
• Charged rechargeable battery. Its voltage must be at least 12 and not more than 14 Volts.
• Low air humidity. It is not recommended to perform measurements in rainy weather.
• Before measurement it is necessary to unscrew all the candles from the cylinders.
• Switch off ignition.

Compression measurement methods

Before you start, you should make sure that this device (compressometer) is suitable for the engine of your car. The standard models of vehicles have a small tip, so they are difficult to use on 16-valve power plants.

The compression can be measured with both open and closed throttle. Experts recommend measuring in both cases. This will identify engine faults (if any) with higher accuracy.

If the measured value has increased or decreased, you can make a diagnosis - your motor is defective, and it needs urgent repairs. But do not forget that there is a small spread of values for the cylinders, which we talked about earlier.

In order to make an accurate measurement, you need an assistant. So, where to start work? First, it is necessary to press the compressometer to the hole in the cylinder, that is, to where you unscrew the candles. At this time, the assistant includes a starter. The last should work approximately 4-6 seconds. Further on the manometer the arrow shows the values - they need to be written down.

After measuring the compression in one cylinder, proceed to the next. Its verification is carried out in a similar manner. Such manipulations should be repeated with all cylinders. Each value is recorded separately in the notebook. It is desirable that before the measurement, the battery should give a voltage of 13-13.5 volts. This will give us a reserve of starting current, since with every second of the starter rotation the charge of the battery drops to a certain level.

After completing the work, you need to install the candles back and re-check the voltage in the battery. If necessary, recharge it by several volts.

Helpful advice

To more accurately determine the current state of the engine, you need not only to focus on the measured compression, but also on a number of other characteristics. This can be the level of vibration, noise, power fluctuations, engine idling, oil and fuel consumption.

Conclusion

So, we found out what compression should be and how it can be measured. The parameters on the instrument allow to accurately determine the internal state of the motor, its remaining life and current malfunctions. And if you find that you do not have compression, such an engine should be subjected to more detailed inspection and repair. Otherwise, after a couple of thousand kilometers, he will destroy himself, and no major repairs will save him.