Engine knocking, what to do and how to determine the cause?

There is no car without an engine and a body. This old adage of drivers makes sense. It is always expensive to change a rotten or crumpled body, and without a working engine, the car will stop. The most important sign of imminent death of the engine is extraneous sound from under the hood.

In this article, we will tell you in detail about the knock on the engine and what it threatens.

Most often, the characteristic dull sound under the hood occurs due to the gap that appears between the parts inside the engine. If you hear a loud knock, then the permissible distance between the parts is exceeded by 2 or more times. The louder the sound, the more the gap “has grown” and the faster the wear of the insides of the unit.

Why there was a knock and what changes await the engine depends on the quality of parts and operating conditions. In any case, the consequences are sad:

  • excessive loads and increased detonation;
  • constant heating of the working mixture and the loss of its qualities due to which engine parts wear out faster.

Engine knock diagnostics

Checking the condition of the motor when a knock appears is carried out according to several parameters.

  • By the nature of the sound: constant, rare or episodic – the frequency of tapping depends on the type and degree of malfunction.
  • By tone of sound: determining the tone of sound is not an easy task. Only an experienced craftsman is able to understand that the resonant knock of an engine in a Korean brand car and a muffled sound of a more powerful engine in a German car mean essentially the same thing – a malfunction of the crankshaft bearings. The fact is that structurally different engines can sound differently, regardless of the state.
  • By location: to obtain the most reliable data, experts use a stethoscope, but if the device is not at hand, you can make a listening device from scrap materials. For example, from a tin can and steel wire.

The knock in the engine is inextricably linked to the operation of the crankshaft, which provides engine speed. Accordingly, the faster the crankshaft rotates, the more often the engine knocks. Depending on the operating mode of the internal combustion engine, the sound may be louder or quieter. It is important to accurately establish the relationship between the increase in the number of revolutions of the internal combustion engine and the sound intensity.

In the process of diagnostics, it is necessary to check at what moment of operation the engine knocks louder. It often happens that at a high temperature in the system (at the moment when the engine oil is at its most liquid and increased in volume), the power plant knocks hard. In some cases, the knocking is heard precisely when the engine is cold, and after warming up, the noise completely disappears or becomes almost invisible.

Reasons for knocking the internal combustion engine

If urgent measures are not taken, the knocking in the engine may increase. In the systems of the gas distribution mechanism, the cylinder-piston group and the crank mechanism, knocking can:

  • piston in the cylinder;
  • piston fingers;
  • a camshaft in the block head;
  • directly the crankshaft in the cylinder block;
  • the so-called rocker arm, as well as the axis of the valve mechanism;
  • valve and valve guide;
  • valve and cylinder head (cylinder head).


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