Contents: Petrol engines ↳ Diesel engine ↳
Compression testing allows you to draw conclusions about the condition of the engine. It helps determine whether the valves and pistons (piston rings) are in order or worn out. In addition, the test results show whether the engine needs to be replaced or whether it can still be overhauled. To test, you need a compression pressure measuring device that is designed specifically for gasoline engines.
Attention! For diesel engines, a compression pressure tester with a large measurement range is used. The pressure difference between individual cylinders should be a maximum of 3.0 bar (in a diesel engine, 5.0 bar). If the pressure in one or more cylinders differs from the other cylinders by more than 3.0 bar (in a diesel engine, more than 5.0 bar), this indicates that the valves are defective, the piston rings or the cylinder running surfaces are worn out. If the wear limit has been reached, the engine must be overhauled or replaced. The results of pressure measurements may vary depending on the use of different measuring devices and the number of starter revolutions. As approximate set values, 11-13 bar should be taken for gasoline engines, and 20-25 bar for diesel engines for compression pressure. The pressure difference between individual cylinders is much more important.
Check the engine oil level, add oil if necessary, otherwise the hydraulic valve lifters will not function properly. If you have added oil, then run the engine for a short time.
To check the compression, the engine temperature must be at least +30°C, the engine must be warm to the touch.
Petrol engines
Turn off the ignition.
Remove the supply wires "1" and "2" from the ignition coil.
Disconnect all spark plug tips by hand or using special pliers, such as HAZET 1849.
After this, clean the spark plug sockets in the cylinder head with compressed air (if available), and unscrew the old spark plugs with a spark plug wrench.
Turn the engine over a couple of times with the starter to remove wear products and scale.
Caution! Shift the transmission to idle and apply the parking brake. Press or screw the compression pressure tester into the spark plug hole according to the operating instructions.
Your assistant should depress the gas pedal all the way and keep it in the down position throughout the entire testing process.
Crank the engine several times until the gauge no longer registers an increase in pressure.
Check all cylinders one by one and record the measurement results.
Finally, screw in the spark plugs, connect the ignition wires, see also item 28.
Diesel engine
Check the valve clearances, they should be correct, otherwise adjust them, see paragraph 1.17.
Turn the ignition key to position "0".
Unscrew the electrical wire from the high pressure fuel pump shut-off valve. Valve position see p. 7.7.
Unscrew the glow plug supply wire on bracket "4", insulate it and put it aside. Wrap the wire tip with electrical tape to insulate. 5 - vacuum pump.
Remove the wires from the glow plugs and unscrew the plugs.
Screw the compression pressure tester in place of the glow plug and turn on the starter until the pointer on the control device stops changing its position. Check all the cylinders one by one.
Set the ignition switch key to position "O".
Install the candles, see p. 7.5.
Connect the wires to the shut-off valve and to the glow plugs.