With the help of a compression check, it is possible to determine the wear of the connecting rod-piston group and the overall wear of the engine.
Check the compression with a special device - a compressor, which can be purchased in auto parts stores.
This is what a compressor meter looks like.
There are variants of compressometers that have a rubber tip instead of a threaded fitting for screwing in instead of a spark plug.
Such compressometers, when checking compression, are simply pressed hard against the candle hole.
You will need a key for 16 to turn out the spark plugs
The procedure for checking compression in the cylinders is shown by the example of the K7J and K7M engines.
Check the compression of the K4M engine in the same way.
The difference is that four ignition coils must first be removed from the spark plugs of the K4M engine
Start the engine and warm it up to operating temperature
We stop the engine and disconnect the wiring harness from the ignition module.
If this is not done, then with the tips of the high-voltage wires disconnected, turning the engine starter can lead to a breakdown of its high-voltage circuit.
Unscrewing all spark plugs
Turn off the fuel pump by removing the fuel pump relay from the mounting block in the engine compartment.
Screw the compressor into the candle hole of the cylinder being checked (if it is threaded, if with a rubber tip, then insert and press it to the candle hole)
The assistant presses the gas pedal all the way to fully open the throttle.
Turns on the starter and scrolls the crankshaft of the engine until the pressure in the cylinder stops increasing (according to the indication of the compressor).
In order for the compressor readings to be correct, the crankshaft must rotate at a speed of 180-200 min -1 or higher, but not more than 350 min -1.
Having fixed the readings of the compressor, set its arrow to zero by pressing the air release valve.
Repeat operations 5-8 for the remaining cylinders.
The pressure should not be lower than 1.0 MPa and should not differ in different cylinders by more than 0.1 MPa.
Reduced compression in individual cylinders may occur as a result of loose fitting of valves in the seats, damage to the cylinder head gasket, breakage or burning of piston rings.
Reduced compression in all cylinders indicates wear of the piston rings.
To find out the reasons for insufficient compression, pour about 20 ml of pure engine oil into the cylinder with reduced compression and measure the compression again.
If the readings of the compressor have increased, the piston rings are most likely to malfunction.
If the compression value remains unchanged, this indicates a loose fit of the valve plates to their seats or damage to the cylinder head gasket.
The reason for insufficient compression can also be found out by supplying compressed air to the cylinder in which the piston is pre-installed in the TDC of the compression stroke.
To do this, remove the tip from the compressor meter and attach the compressor hose to it.
Insert the tip into the candle hole and supply air to the cylinder at a pressure of 0.2-0.3 MPa.
To prevent the engine crankshaft from turning, turn on the upper gear and brake the car with the parking brake.
The air outlet (leakage) through the throttle assembly indicates the leakiness of the intake valve, and through the muffler - the leakiness of the exhaust valve.
If the cylinder head gasket is damaged, air will escape through the neck of the expansion tank in the form of bubbles or into the adjacent cylinder, which is detected by a characteristic hissing sound.