5.2. Compression check in cylinders

Compression (pressure in the end of a compression step) in cylinders — the major indicator for diagnostics of a condition of the engine without its dismantling. On its average value and on a difference of values in separate cylinders it is possible with sufficient degree of accuracy to define degree of the general deterioration of details of shatunno-piston group of the engine, to reveal malfunctions of this group and details клапанного the mechanism.

Check a compression the special device — компрессометром which can be got now freely in large shops of autospare parts.

THE NOTE So looks компрессометр, used for an illustration of the given book. There are variants компрессометров at which instead of the carving union for вворачивания instead of a spark plug the rubber tip is established. Such компрессометры at compression check simply strongly press to a candle aperture.

THE PREVENTION The important condition of correctness of indications at compression check is serviceability of a starter and its electric chains, and also full заряженность the storage battery.

1. Start up the engine and warm up it to working temperature.

2. Stop the engine, remove tips of wires from spark plugs and turn out all candles (Replacement and service of spark plugs see).	3. Disconnect pad a plait of low-voltage wires from the ignition coil, having disconnected thereby ignition system.

    

THE PREVENTION Проворачивание the engine a starter at the disconnected tips of high-voltage wires and not disconnected coil of ignition can lead to breakdown of its high-voltage chain.

4. Disconnect the fuel pump, having taken out a safety lock №11 …	5. … or the relay of the fuel pump in the assembly block (Assembly blocks see).

6. Screw in a candle aperture of the checked cylinder компрессометр.

7. Press an accelerator pedal against the stop completely to open throttle заслонку.

8. Include a starter and turn it a cranked shaft of the engine until pressure in the cylinder will not cease to increase. It corresponds approximately to four steps of compression.

THE NOTE For reception of correct indications компрессометра the cranked shaft should rotate with frequency of 180-200 mines-1 or above, but no more than 350 mines-1.

9. Having written down indications компрессометра …	10. … establish its arrow on a zero, having pressed the valve of release of air.

THE NOTE At компрессометров other design of the indication can be dumped in other ways according to the instruction to the device.

11. Repeat operations of subitem 6-10 for other cylinders. Pressure should be not more low 1,0 МПа and should not differ in different cylinders more than on 0,1 МПа. The lowered compression in separate cylinders can result from leaky landing of valves in saddles, damages of a lining of a head of the block of cylinders, breakages or burnings of piston rings. The lowered compression in all cylinders specifies in deterioration of piston rings.

12. For finding-out 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 компрессометра have raised, malfunction of piston rings is most probable. If the compression remained invariable, means, plates of valves leaky adjoin to their saddles or the lining of a head of the block of cylinders is damaged.

GOOD ADVICE The reason of an insufficient compression can be found out also giving of compressed air in the cylinder in which the piston is preliminary established in ВМТ a compression step. For this purpose remove with компрессометра a tip and attach to it a compressor hose. Insert a tip into a candle aperture and submit to the cylinder air under the pressure of 0,2–0,3 МПа. That the cranked shaft of the engine was not turned, include the higher transfer and brake the car a lay brake. The exit (leak) of air through throttle knot testifies about негерметичности the inlet valve, and through the muffler — about негерметичности the final valve. At damage of a lining of a head of the block of cylinders air will leave through a mouth of a broad tank in the form of bubbles or in the next cylinder that is found out on a characteristic hissing sound.