5.4. Check of a compression in cylinders

Compression (pressure at the end of a compression step) in cylinders — the major indicator for diagnostics of a condition of the engine without its dismantling. And on a difference of values in separate cylinders it is possible with sufficient degree of accuracy to determine degree of the general wear of details of tsilindroporshnevy group of the engine by its average value, and also to reveal malfunctions of this group and details of the valvate mechanism.
Check a compression the special device — kompressometry which can be got freely in large shops of auto parts now.

So looks компрессометр, used for an illustration of this book. There are options of kompressometr at which instead of the carving union for a vvorachivaniye instead of a spark plug the rubber tip is established. Such kompressometra when checking a compression just strongly press to a candle opening.

Important condition of correctness of indications when checking a compression is serviceability of a starter and its electric chains, and also full state of charge of the rechargeable battery.

1. Launch the engine and warm up it up to the working temperature.
2. Reduce pressure in an engine power supply system (see. "Pressure decrease in an engine power supply system"). Do not install a safety lock of a chain of the fuel pump in the central assembly block.
3. Remove tips of wires from spark plugs and turn out all candles (see. "Replacement and service of spark plugs").
4. Disconnect a block of a plait of low-voltage wires from the ignition coil, having disconnected thereby system of ignition.

Provorachivaniye of the engine a starter at the disconnected tips of high-voltage wires and not switched-off coil of ignition can lead to breakdown of its high-voltage chain.

5. Screw in a candle opening of the checked cylinder компрессометр.
6. Press an accelerator pedal against the stop that at a provorachivaniye of a bent shaft a starter the butterfly valve completely opened in the mode of a purge of cylinders of the engine.
7. Include a starter and turn it a bent shaft of the engine until pressure in the cylinder does not cease to increase. It corresponds to about four steps of compression.

For obtaining the correct indications of a kompressometr the bent shaft has to rotate with a speed of 180-200 min.-1 or above, but no more than 350 min.-1.

8. Having written down indications of a kompressometr …
9. … establish it to the shooter on zero, having pressed the valve of production of air.

At kompressometr of other design of the indication can be dumped in other ways (according to the instruction to the device).

10. Repeat operations 5-9 for other cylinders. Pressure has to be not lower than 1,0 MPas and more than on 0,1 MPas should not differ in different cylinders. The lowered compression in separate cylinders can result from leaky landing of valves in saddles, damages of laying of a head of the block of cylinders, breakages or burnings of piston rings. The lowered compression in all cylinders indicates wear of piston rings.
11. For clarification of the reasons of an insufficient compression fill in in the cylinder with the lowered compression about 20 ml of pure engine oil and again measure a compression. If indications of a kompressometr raised, malfunction of piston rings is most probable. If the size of a compression remained an invariable, so plate of valves leaky adjoin to their saddles or laying of a head of the block of cylinders is damaged.

Good advice
The reason of an insufficient compression can be found out also supply of compressed air in the cylinder in which the piston is previously installed in compression step VMT. For this purpose remove a tip from a kompressometr and attach to it a compressor hose. Insert a tip into a candle opening and give to the cylinder air under pressure of 0,2–0,3 MPas. In order that the bent shaft of the engine was not turned, include the highest transfer and slow down the car the parking brake. An exit (leak) of air through throttle knot testifies to leakage of the inlet valve, and via the muffler — to leakage of the final valve. At damage of laying of a head of the block of cylinders air will come out through a mouth of a broad tank in the form of bubbles or in the next cylinder that is found on the characteristic hissing sound.