The compression (pressure in the cylinder at the end of a compression step) characterizes a condition of tsilindroporshnevy group (TsPG). At serviceable power supply systems and ignitions in case of decrease in engine capacity carry out its check.

For compression check the engine should be warmed up to working temperature, level of oil should be normal, and the storage battery should be charged.

On engines with system of injection of fuel before check remove the fuse of the fuel pump from the assembly block of the relay and safety locks. Then start up the engine and wait its stops.

Compression define in the following order:

– disconnect tips of high-voltage wires from spark plugs;

– turn out spark plugs;

– establish a rubber tip компрессометра in an opening of a spark plug of the first cylinder;

– press against the stop a pedal of an accelerator and turn a cranked shaft a starter on 10-15 turns (the assistant carries out), thus watch indications компрессометра;

– fix the highest value of pressure;

– repeat operations for the remained cylinders.

If TsPG condition in norm, pressure quickly increases.

Minimum admissible pressure in the cylinder, MPa (kgf/cm2):

        RP and AAM 0,70 (6,86) engines

 other       engines 0,75 (7,35).

The difference in pressure indications between cylinders should not be more than 0,07-0,1 MPas. If in one cylinder the compression is much lower, than in the others, means, leakage of air via valves in it takes place.

Low pressure in the cylinder on the first step of compression, and then its gradual increase at the subsequent point to wear of piston rings. The low compression during the whole time of measurement testifies to leakage of air via valves or "burn-out" of laying of a head of the block of cylinders. Leak via the valve can be caused it by leaky closing because of a deposit on its rod and a plate, a bend of a rod, "burn-out" of a saddle or a plate of the valve.

For establishment of the reason of an insufficient compression add in the cylinder about 20 cm3 of fresh engine oil through an opening for a spark plug, and then repeat test. If pressure increases, it testifies to wear of piston rings if pressure does not increase — about leaks via valves or "burn-out" of laying of a head of the block of cylinders.

If two adjacent cylinders have equally low values of pressure, it is the most probable that laying of a head of the block of cylinders between them "burned through". It confirms also emergence of cooling liquid in chambers of combustion or on the index of level of engine oil.

After check establish spark plugs, connect to them high-voltage wires and establish a safety lock of the fuel pump.