As you know, the engine is the heart of the car. A lot depends on its serviceability. An important factor determining its condition is compression in the engine cylinders. This parameter is different on diesel and gasoline cars. What is engine compression, how to measure it and what are the normal indicators? You will learn about all this from our article today.
Characteristic
So what is compression in the engine cylinders? This is a parameter indicating the pressure that is created in the cylinders at the end of the compression stroke. The technical condition of the engine depends on the value of this figure.
Therefore, the compression check in the cylinders of the car engine is taken as a diagnostic factor, which allows to evaluate the health of the power unit.
What is the norm?
If we talk about gasoline engines, then this parameter averages from 11 to 12 kilograms per square centimeter. Such compression on most cars of the brand "Daewoo", "Ford", "Kia", "Toyota" and others. The highest is Mazda’s sixth series. So, the manufacturer allocates a norm of 16 kilograms per square centimeter. But there are engines where the norm is considered an indicator of 7-7.5. As a rule, these are old deformed motors with a low compression ratio. A vivid example is the ZIL-130 or GAZ-3307 engine. The compression rate in the cylinders of these trucks is 7 kilograms per centimeter square. This is done in order to switch the engine to lower octane gasoline. As practice shows, such engines easily "digest" the 76th and 72nd gasoline, even of the most dubious origin.
Now let's move on to diesel engines. Here the average is in the region of 25-30. A critical indicator for diesel engines is a pressure of 20 kilograms per square centimeter. In this case, the motor may not even start.
Is a runaway in the readings permissible?
It is worth noting that the compression in the engine cylinders should be not only high, but also uniform. If in one cylinder this figure is 12.8 kgf, and in the other - 10, this is not good. The manufacturer allows a take-off of not more than one kilogram per square centimeter. A strong differential may indicate a malfunction. As for diesel engines, here the error can be 3 atmospheres, but no more.
Measurement conditions
The most important conditions for checking compression in the engine cylinders are a warm engine and an open throttle. Measurement is carried out with the candles unscrewed and with a working battery.
About compressometers
It is with this device that this parameter is measured. There are many models of compressometers, but they differ only in their design. So, this device consists of a tip (it is installed in the spark plug hole), a pressure gauge and a check valve. Elements are interconnected by a thick hose or a metal tube.
Experts advise buying the first option, since part of the device can rest on other attachments due to the rigid rod. There are also compressometers that are screwed into the candle hole or simply pressed against it.
Checking engine compression - helpful hints and steps
So, first we warm up the engine to operating temperatures. Then we suppress it, open the hood and unscrew the candles. Next, we install the tip of the compressor in the hole (screw it into the thread or simply press it) and call the assistant. He will twist the starter at your command. You need to rotate it for about two to three seconds. No longer needed - the compression will not be higher, and the battery will discharge significantly. Next, we record the readings of the manometer and write them in a notebook. Then go to the second cylinder. The procedure is repeated in a similar manner. You do not need to screw a candle onto the cylinder - only after all measurement procedures have been completed (otherwise the engine will start and will troit).
After completing the measurements, install the candles back and analyze the result.
Measurements on the diesel engine
Earlier, we examined the procedure for measuring compression in the cylinders of a gasoline engine. But in diesel spark plugs there is no - the mixture ignites from compression. How to measure compression on such motors? Everything is simple. First you need to prepare a specialized compressometer with a scale of up to 60 atmospheres. It should come with an adapter in the form of a nozzle. Next, turn off the fuel supply. To do this, de-energize the solenoid valve. It is worth noting that compression measurement in the cylinders of a diesel engine can be performed only with one injector removed.
So, we start the starter and twist it for two to three seconds. During this time, the arrow should rise to 25-30 (and possibly more) atmospheres. Next, the nozzle is installed in place and the next one is unscrewed, on the adjacent cylinder. All data should be recorded in a notebook or photograph.
What can cause low compression?
If this parameter is significantly different from the factory one in a smaller direction, this is a very bad sign. The motor may need major repairs. And the reasons for low compression can be:
- Scuffing on cylinder walls. They are formed due to metal chips that occurs inside the cylinders during the operation of the internal combustion engine. Chip indicates a significant output - the motor may have experienced oil starvation or the rings are lying.
- Burnout head gasket. As a result, the tightness of the valve-piston-cylinder system is impaired.
- Crack in the block. This phenomenon is due to overheating of the engine.
- Valve leaks. May be caused by burnout or incorrect adjustment. Also note that the valve clearance is violated even in the presence of hydraulic lifters. Over time, their oil holes become clogged. The elements are no longer able to compensate for the required gap, and the valves do not work correctly (they do not close completely, due to which the pressure at the end of the compression stroke drops significantly).
- Coking of piston rings. The problem may be caused by the use of low-quality fuel or an untimely oil change.
- Natural wear. Over time, the gap between the walls of the cylinders and the piston increases. Because of this, the required pressure for the working process is not formed in the chamber. Usually this happens after 300-400 thousand kilometers.
Can this problem be delayed? In order not to experience problems with low compression, it is only enough to change the oil, filters and spark plugs in time (if you have a gasoline engine). This is the only way to extend the life of your engine.
Conclusion
So, we found out what compression is in the engine cylinders and for what reasons it can change. If this parameter is lower than the factory one, you should immediately take measures to repair the engine. The exact reason can already be determined by the minder. But usually these are rings or burnt valves.