BMW 3 series E30

Since 1983-1994 of release

Repair and car operation

3.2.4. Compression check in engine cylinders

THE GENERAL DATA

Results of check of a compression in engine cylinders allow to judge a condition of group of details in the top part of the engine (pistons, rings, valves and a lining of a head of the block of cylinders). Namely, compression reduction can be caused негерметичностью chambers of combustion owing to deterioration of piston rings, damage of heads of valves and saddles, прогара linings of a head of the block of cylinders.

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The prevention

For reception of exact results of check the engine should be heated-up to normal temperature, and the battery is completely charged.

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PERFORMANCE ORDER

1. Begin that clear sites near to spark plugs for what blow compressed air (in the absence of the compressor blow sites automobile, or even bicycle, the pump). It is necessary to exclude dirt hit in cylinders at compression measurement. 2. Turn out spark plugs. 3. Completely open throttle заслонку and fix in such position. 4. Disconnect the central high-voltage wire from a cover of the distributor of ignition, connect it to weight on the block of cylinders. For reliability connection with weight execute by means of a special short-circuiting piece of a wire with clips of alligator type on both ends. Also will not prevent to remove a safety lock of electronic system of injection of fuel on the assembly block that will provide a blackout of the electric fuel pump at compression measurement. 5. Insert a compression measuring instrument into an aperture for a candle. 6. Include a starter and turn коленвал on some turns, watching indications of a manometre of a measuring instrument of a compression. On the serviceable engine pressure should accrue quickly. Low pressure after the first piston stroke and slow increase at the subsequent steps of compression specifies in deterioration of piston rings. If after the first piston stroke pressure low, and at the subsequent steps of compression does not increase, the reason is leak in valves or негерметичность linings of a head of the block of cylinders (the reason formation of cracks in a head also can be). Compression decrease can be caused also deposit adjournment on heads of valves. Write down the greatest value of a compression. 7. Repeat procedure of measurement for other cylinders, results compare to the standard data. 8. Through an aperture for a candle enter into each cylinder of a few oil for the engine (about three full шприцевых butterdishes), then repeat tests. 9. If after introduction of oil the compression has raised, it is possible to draw an unequivocal conclusion that piston rings are worn out. If the compression increases slightly leak occurs through valves, or a lining of a head of the block of cylinders. Leak through valves can be caused a burn-out of saddles and / or facets of valves, and also deformation of cores of valves, or formation on them of cracks. 10. If a compression equally low only in two next cylinders most a plausible reason is the lining burn-out between these cylinders. Occurrence in chambers of combustion or in картере коленвала the block of cylinders of traces of a cooling liquid will be acknowledgement of this conclusion. 11. If value of a compression in one of cylinders more low for 20 percent, than in other cylinders and the engine unstably idles, deterioration of a cam of the cam-shaft operating the final valve can be the reason. 12. If value of a compression exceeds norm the combustion chamber is covered by deposit adjournment. In this case a head of cylinders it is necessary to remove and remove a deposit. 13. If the compression in all cylinders low, or strongly differs for different cylinders it is necessary to conduct tests of chambers of combustion for tightness for what it is necessary to address in a specialised workshop. As a result of tests places of leaks should be precisely established and the quantitative characteristic of leak is given.