At combustion of gas mixture in chambers of combustion of cylinders pressure about 6 MPas that creates high loads of pistons and piston rings, walls of cylinders, and also saddles and consolidations of valves is created.

At rather small consumption of gasoline the engine shows the best productivity at good tightness of piston rings when all gas mixture is used for useful work. In case of violation of tightness of valves and piston rings the raised consumption of oil and fuel, decrease in capacity and the complicated start-up of the cold engine, and also increase in environmental pollution is observed. If it so, is necessary to carry out measurement of a compression of separate cylinders of the engine by means of the special device — компрессометра on the basis of what is defined, valves and piston rings are how tight.

Measurement of a compression carry out in the following order:

- warm up the engine to working temperature as hot piston rings provide the best tightness;

- disconnect ignition;

- turn out all spark plugs;

Fig. 159. A three-contact shtekerny block — 1

- remove the sensor of provision of a cranked shaft and disconnect a three-contact shtekerny block 1 (fig. 159) of the coil of ignition;

- open a butterfly valve with the assistant who will press an accelerator pedal;

- densely insert a rubber cone компрессометра into an opening of the first candle;

- with the assistant scroll the engine a starter and measure compression size in the engine cylinder. The engine scroll until the arrow компрессометра will not rise any more, i.e. will show the maximum value of a compression;

- in the similar way check in turn other cylinders of the engine.

It is considered normal if value of a compression in one of cylinders does not fall below 80 % from the maximum, all cylinders received at measurement.

The low compression or having big distinctions in different cylinders, grows out of wear of piston rings that it is possible to determine by the raised consumption of oil also.

The size of a compression of the engine should be not less than 750 kPas. If the received result of measurement of a compression approximately is equal to this size, fill in a little engine oil in the engine through an opening of a spark plug and repeat measurements. If after that:

- the result will appear better, it is possible to assume that the reason of a low compression are worn-out piston rings or cylinder walls;

- the result remained approximately the same, the reason of a low compression most likely are one or a little badly working valves or there can be not tight a laying of a head of the block of cylinders. In any case it is necessary to remove a head of the block of cylinders and to carry out careful check for definition of a cause of defect.

On sale there are additives to oils which after their gulf provides additional tightness of piston rings. The effect in most cases gained from it appears very nondurable, however there are cases when it really helps. On HUNDRED "Volkswagens" it is possible to receive information for purchase of the best production such.