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 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 conrod and piston group of the engine by its average value, 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 conditions of correctness of indications when checking a compression are 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 a power supply system (see. "Pressure decrease of fuel in an engine power supply system"). After pressure decrease into place do not establish a safety lock of the fuel pump to switch-off the fuel pump.
3. Remove coils of ignition and turn out all candles (see. "Replacement and service of spark plugs").
4. Screw компрессометр in a candle opening of the checked cylinder.
5. Press an accelerator pedal against the stop completely to open a butterfly valve.
6. 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.

7. Having written down indications of a kompressometr, 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).

8. Repeat operations 4-7 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.
9. For clarification of the reasons of an insufficient compression fill in in the cylinder with the lowered compression about 20 cm3 of pure engine oil and again measure a compression. If indications of a kompressometr raised, malfunction of piston rings is most probable. If value of a compression remained invariable, so plates of valves leaky adjoin to 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.