2.2.3. Check of extent of compression

Check of extent of compression shows what mechanical condition of the top level of the engine (pistons, rings, valves, laying of a head). In particular, check can show that extent of compression is lowered because of the leak caused by wear of piston rings, defective valves and saddles or because of the burned-through laying of a head of the block.

At this check the engine has to be heated-up up to the normal working temperature, and the rechargeable battery - completely


  1. Before removal of spark plugs clear area around them (it is necessary to apply if it is available, compressed air, differently it is possible to use the bicycle pump or a small brush). The purpose consists in that when checking not to allow hit in dirt cylinders.
  2. Remove all spark plugs from the engine (watch Chapter Routine maintenance of the car).
  3. Block a butterfly valve in completely open situation or let the assistant hold a pedal in the pressed situation.
  1. On carburetor models disconnect a wire of low voltage from the ignition coil. On models with injection of fuel switch-off the fuel pump and a chain of ignition, having removed the main relay (it is specified by an arrow).
  1. It is necessary for prevention of ignition of fuel which could be injected into a motive compartment. Usually main relay is located under a cowl near the panel of safety locks, however for exact definition of an arrangement on your model address the Head Sistema of onboard electric equipment.
  2. Establish in an opening of a candle No. 1 компрессометр (the cylinder No. 1 is located from a radiator).
  3. Starter turn the engine, at least, on seven steps of compression and watch indications of the compressor. On the serviceable engine extent of compression will quickly increase. Low extent of compression in the first step with gradual increase in the subsequent steps testifies to wear of piston rings. The low extent of compression in the first step which is not increasing in the subsequent steps indicates leaks in valves or on прогар laying of a head of cylinders (the crack in a head of cylinders can also be to it the cause). The deposit on internal surfaces of heads of valves can also cause low extent of compression. Write down the greatest measured value.
  4. Repeat operation for other cylinders and compare results to values of extent of compression in the Size table and adjusting data at the end of the Management.
  5. If extent of compression low, fill in through openings for spark plugs in each cylinder a small amount of motive oil (having pressed, about, three times a butterdish of plunger type) and repeat check.
  6. If after oil addition extent of compression increased, then piston rings are definitely worn-out. If extent of compression considerably did not increase, then in valves or through laying of a head of cylinders there is a leak. Leak in valves can be caused by an obgoraniye of saddles of valves and/or facets, and also a curvature of valves and existence of cracks and dents.
  7. If two next cylinders have equally low extent of compression, then it is quite probable that laying of a head of cylinders between them burned through. Existence of a cooler in combustion chambers or a case will confirm this offer.
  8. If extent of compression in one of cylinders is 20% lower, than in the others, and the engine idles slightly unevenly; that the final cam of the camshaft is perhaps worn-out.
  9. If extent of compression is unusually high, then combustion chambers are probably covered with a deposit.
  10. In this case it is necessary to remove a head of cylinders and to remove a deposit.
  11. If extent of compression is lower than norm or strongly differs between cylinders, then it is useful to carry out diagnostics of leaks in auto repair shop. This check will precisely indicate the reason of leaks and its degree.