At gas mixture combustion in chambers of combustion of cylinders pressure of an order 6 МПа is created that creates high loadings on pistons and piston rings, walls of cylinders, and also saddles and consolidations of valves.

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 infringement of tightness of valves and piston rings the raised expense of oil and fuel, decrease in capacity and the complicated start-up of the cold engine, and also environmental contamination increase is observed. If it so it is necessary to spend measurement of a compression of separate cylinders of the engine by means of the special device — компрессометра on the basis of what it is defined, valves and piston rings are how much tight.

Compression measurement spend in a 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. Three-contact штекерная колодка — 1

- Remove the gauge of position of a cranked shaft and disconnect three-contact штекерную колодку 1 (fig. 159) ignition coils;

- Open throttle заслонку with the assistant who will press an accelerator pedal;

- Densely insert a rubber cone компрессометра into an aperture 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 up by turns 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 the big distinctions in different cylinders, grows out of deterioration of piston rings that it is possible to define also under the raised expense of oil.

The size of a compression of the engine should be not less than 750 кПа. If the received result of measurement of a compression approximately is equal to this size fill in a few engine oil in the engine through an aperture 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 the 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 lining 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 spend 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 not long-term, however there are cases when it really helps. On HUNDRED «Volkswagen» it is possible to receive the information for purchase of the best production such.