Extraneous noises and engine knocks can be strong and weak, dull and sonorous - all of them not only reduce the comfort of driving and irritate the hearing, but also signal malfunctions in the engine components and assemblies. Significant loads on its parts are periodic in nature and depend on the speed. Therefore, several thousand blows every minute can lead to very sad consequences.
In most cases, knocks occur in the contact area of parts with an increased gap between them. With normal lubrication and cooling, the gap must be exceeded twice the normal value for knocking to occur. And the larger this gap, the stronger the knock is heard.
Obviously, the knock occurs when one part hits another. This means increased loads on these parts in the places of their collision, and, consequently, increased wear and destruction of the impacting surfaces. Therefore, shocks tend to get worse over time until all of this leads to breakage.
The rate of development of this process depends on the design, material and production technology of parts, loads on them, lubrication and cooling. For example, knocking on the gas distribution mechanism can last many thousands of kilometers before causing damage. And knocks in the crank mechanism are able to bring it out and build it for a couple of hundred or tens of kilometers.
Most often, such knocks are observed in engines with high mileage and significant wear of parts. That is, the main reason is natural wear and tear as a result of long-term operation.
In addition, shocks can also occur with normal clearances between parts that do not show signs of wear. This occurs when excessive loads, misalignment and jamming of parts, a decrease in oil viscosity. In this case, the knocking disappears when the causes are eliminated, if the striking parts did not have time to get damaged.
Knocking due to misalignment of parts is due to human factors. For example, the deflection of the connecting rod due to a water hammer after forcing a puddle or a defective part installed by a mechanic. The use of parts with incorrect geometric dimensions always leads to increased stress on them. This is accompanied by a violation of its temperature regime of operation and deterioration of lubrication. All this leads to rapid wear, increased clearances and knocking.
And the last, most unconventional reason is a knock when non-conjugated parts come into contact. It occurs only when one of them is severely deformed. For example, a hydraulic shock in a cylinder causes the connecting rod to shorten, causing the piston to touch the crankshaft counterweights at bottom dead center. It happens that the edges of the head gasket hang down into the cylinder, and the pistons protrude upward above the plane of the block. Rarely, but there is an incorrect phase setting, when the valves touch the pistons during operation.
In any case, the appearance of a knock in the engine signals the need for its early diagnosis. The amount of repair work depends not only on its nature, but also on the speed of the repair that has begun and on the correctness of the diagnosis.
