Engine knocking - the most common causes and their solutions

Engine knocking is a common problem for cars that have been used without proper care for more than 10 years. They are often accompanied by other engine noise and vibration. This is also true for cars with a mileage of more than 100 thousand km. Gasoline or diesel engine – it doesn’t matter. If you do not undergo diagnostics at least once a year, then you are likely to encounter these problems in a new car or motorcycle. Since the engine consists of many complex components, various factors can be the possible cause of such problems. Each of these problems signals a specific threat and requires its own method of elimination.

Two main causes of knocking

Knowing why the engine knocks, you can then act in accordance with the cause. According to experts, knocking in the engine when starting occurs only for 2 general reasons.

This is either worn out elements inside the power unit;
Or, if the engine starts knocking, detonation has occurred.

Detonation

Let's start with detonation, as it can create irreparable problems. Detonation is already an alarming signal to the driver, who must know what it is and what are the reasons for this phenomenon when starting or operating the engine.

Detonation occurs due to improper distribution of the air/fuel mixture inside the cylinders. This, in turn, results in uneven combustion. Fuel, gasoline or diesel fuel, burns in the cylinders of car power units, if normal conditions are provided, during the process of mixing with air. All motorists, even beginners, should know this.

When detonation occurs, an explosion occurs inside the cylinders, the mixture burns unevenly, which can lead to damage to the walls or the piston itself.

This phenomenon has been known for a long time, since the creation of internal combustion engines. Described in almost all sources as automatic gas ignition. Previously, it was not possible to thoroughly test this phenomenon. For this very reason, in those days it was thought that detonation was related to ignition, but this is not so.

The knock sensor was specially invented and is equipped with almost most modern cars. This regulator perceives the mechanical energy of vibrations occurring in the cylinders, and then transmits an electrical impulse to the ECU.

Knock sensor

It is noteworthy that during detonation there is a clear knocking sound, more loud. Any specialist or experienced driver with experience can recognize detonation by ear. The knocking appears in this case due to various additional loads on the machine’s engine.

This may be a sudden acceleration;
Slow movement, for example, on inclines;
Driving in the wrong gear and much more.

So, the reasons why detonation occurs at startup.

Very high temperature of the cylinders or piston in various areas;
Too high a compression ratio, which occurs due to an excessive layer of carbon deposits remaining on the piston crown;
Heavy load on the engine, occurring at low crankshaft speed;
Poor quality of fuel (gasoline/diesel) filled at Russian gas stations;
Hot carbon deposits remaining in the combustion chamber;
Spark plugs, which can also be a cause if they are faulty or do not correspond to the thermal conditions.

Wear of engine components

A knock can occur, as mentioned above, due to wear, for example, of connecting rods or bearings. If such a knock has already appeared, then nothing will help: neither the use of more viscous oil, nor later ignition, nor various linings or “fur coats” that are placed under the liners. Although for a while, it will still help. In particular, a worn-out connecting rod hitting the crankshaft journal will no longer make such a strong knock, but only a muffled, almost imperceptible one.

connecting rod

The connecting rod knock did not spare the diesel engine either. True, the noise picture here may be somewhat different. When the car is moving, the pistons of the diesel unit come close to the cylinder head, which forces them to touch the cylinders. Even after the “knock” cylinder stops working, the rumble remains and continues for some time. It is worth noting that you cannot drive a car, diesel or gasoline, with the engine knocking because of the connecting rod, especially when it’s hot. Other parts of the power unit may also knock. These could be, for example, valves, a fuel pump drive that produces an unpleasant sound when knocking, pulleys, etc. A diesel engine can present another surprise to the car owner. The knock of plunger pairs, with which nothing can be done. Although you can drive with such a knock for quite a long time, because it does not affect anything. According to experts, it may happen that after three years such a knock will still lead to wear of some important components, and the car may consume much more gasoline than necessary.

IMPORTANT! At the same time, the sound can come not only from the engine. Apart from small stones falling into the car, the air conditioner, suspension, etc. can make noise. The problem of noise is relevant for any internal combustion engine, be it 22sdi or 3sz.

Phase shifters

They can be installed on machines with chain and belt mechanisms. Inside the phase shifter there are two moving parts, one is attached to the camshaft, the other engages with a belt or chain. When oil is supplied, they can move against each other (I won’t go into detail now, but I already have an article ).

There are special partitions between the chambers that control the oil pressure in the chambers. Over time, both these partitions and the walls of the phase shifter can wear out. And a knocking sound similar to a cracking sound may appear. It comes from the top of the engine

Other causes of engine noise

The list of causes of creaking or knocking in engines is extensive - automotive experts name 120-130 malfunctions of varying severity that lead to noise. The most private of them:

Arbitrary expansion of gaps in valves.
Crack in the valve spring.
Broken cams or camshaft valves.
Broken crankshaft connecting rod bearings.
Piston failure.
Low oil pressure (pay attention to the sensor).
Spontaneous ignition of a flammable mixture (detonation).
Arbitrary expansion of the gaps between valves and liners.
The chain hits the damper.

Each problem requires its own solution. It is better to search for such a solution together with the specialists of the service station, but it would not be amiss to at least roughly understand what, where and why the knocking in the engine occurs. At a minimum, this will allow you to plan for repair costs. Some problems can be resolved on your own.

Engine knocking at idle

It is believed that the cause of this noise is a malfunction of the valves. It is not always so. To try to independently determine the source of the noise, you can use a car stethoscope.

Engine knocking at idle is actually more often associated with valves. If the sounds disappear when you gain speed, this is probably the reason. Often the problem does not go away, the sound of faulty valves is simply drowned out by a running engine. There is no point in delaying the adjustment of valves, since their incorrect functioning leads to accelerated wear of parts of the gas distribution system.

The easiest way to adjust valve play is to tighten the rockers or replace the washers. A knock in a VAZ 2109 engine often indicates wear on the cylinder head. This does not affect the driving performance, but it will not solve the issue.

A malfunction in hydraulic compensators is also a common source of knocking. If it does not go away after warming up, the cause is usually the oil. It is necessary to check the lubricant level in the crankcase and, if necessary, add lubricant. If this does not help, you should check or replace the fuel pump. If the problem is not solved, the service life of the cylinder head will be significantly reduced.

A worn piston also makes a loud knocking noise. If using a stethoscope it is determined that the sound is coming from the middle part of the cylinder, it is most likely the piston. If the knocking noise disappears at rpms of 2 thousand and above, then the probability of problems with the piston is 90%. The most reasonable thing is to contact specialists, since a major overhaul of the engine is possible. You can try changing the pistons and crankshaft liners by grinding it.

Other common causes include a faulty connecting rod bushing. Worn camshaft bearings or pumps produce a dull knock.

Knock in engine when starting cold

Among the causes of noise when the engine knocks when cold, experienced auto mechanics identify five main ones.

Incorrect valve adjustment. It is necessary to inspect the thermal gaps; usually the problem with a high mileage engine is associated with them.
Wear of hydraulic compensators. It is better to change them, and at the same time change the oil and filter.
Incorrect main bearing clearance - more than required. In this case, the knocking noise will be heard until the oil pressure reaches a high level. If during warming up and after it the oil pressure level “jumps”, the problem is in the oil pump.
The timing mechanism often knocks if the gaps in the beds increase too much. This knocking noise goes away after it warms up.
The most serious problem that a knocking sound indicates when starting from a cold state is wear or defect of the piston, as well as wear of the rings.

Valve knock

The appearance of extraneous sounds usually indicates engine wear, especially if it begins to stall. In this situation, it is necessary to carry out a full diagnosis, repair or replacement of parts.

IMPORTANT! There may be a difference between knocking noises in a cold and warm engine. But often turning the engine on at high speeds simply drowns out the valves and pistons.

Since the motors differ in design, the reasons for the noise are different for each. For example, in a Priora sedan the tension roller of the alternator belt may be knocking.

Valve knocking on a cold engine

A common cause is incorrect clearances between the arms and camshaft cams. Due to too much distance, the cam hits the rocker, producing a loud metallic knock. The larger the gap, the louder the sound.

Another common problem is that the valve clearance is too narrow. Over time, the clamped valves stop closing correctly, the engine will begin to overheat, and compression will drop. In addition to the obvious problems, this leads to excessive fuel consumption. You can avoid the problem by adjusting the valves after 10-15 thousand kilometers.

The third main reason is detonation (on an automatic transmission this can be seen by random gear shifting). As a result of micro-explosions, the valves begin to knock. But the problem is not with them. The main signs of detonation are changes in smoke from the exhaust pipe, vibration and a decrease in engine power.

Drivers also experience a knocking noise in a cold engine when the pusher wears out.

Valve knocking on a hot engine

On a hot engine, valves may knock due to low oil pressure. First you need to make sure that the condition (contamination) of the oil is normal, and its technical characteristics (viscosity, etc.) correspond to the engine. If after replacement the pressure measurement does not show an improvement, the matter is due to wear or defects in parts.

Connecting rod knock

The knock of a connecting rod is the most dangerous signal of all extraneous noise. He says the motor will break down any moment. To the ear it sounds like a metallic, slightly muffled knock. But acoustic diagnostics are difficult due to differences in engine designs. One of the simple ways to determine that a connecting rod is knocking is to turn off the spark plug in the cylinder that is suspected.

Injector knock

In a diesel engine, knocking often comes from the injectors. This usually happens due to increased fuel supply. This is caused by misadjustment of the fuel equipment. To the ear, this is a characteristic clicking sound, sometimes reminiscent of a chirping sound. The sound is coming from the top of the engine. If you hold the injector fuel line, you will feel vibration.

Knocking fingers

Piston pins can knock for two main reasons: a malfunction or detonation (the problem is related to inappropriate fuel).

What if you hear a knock and then it goes away?

A common cause of knocking noises heard when the engine is cold and disappears when the engine is warm is wear of the cylinder liners, that is, an expansion of the gap between the piston and the cylinder wall. When warmed up, the pistons expand, the gap decreases, and the knocking noise disappears.

If an extraneous knocking noise begins when the speed is increased, this indicates extreme wear of the crankshaft (a knock is heard in the cabin on the left side) or parts of the CPG. When the engine is cold, the oil is more viscous and fills the spaces in the gaps. While the engine is running, it liquefies, resulting in a knocking sound. It disappears when the engine cools. Also, a common cause of noise can be a damaged pin or a crack in the piston skirt.

Metallic knock

This type of sound indicates that metal parts are knocking against each other. If the sound resembles a metallic ringing, detonation is occurring in the engine. It is often accompanied by thick black smoke coming out of the muffler. A weakened chain may sound - such a knock is clearly audible and resembles a click. It goes away or gets quieter when you give it gas. A metallic knock accompanied by a quiet rumble is often produced by the gearbox . If you squeeze the clutch while the engine is running and the knocking goes away, that’s the problem.

A loud knock

A rhythmic, ringing knock indicates the need to replace the connecting rod bearings. If it goes away when the ignition is turned off, the probability of this option is 90%. But these sounds can appear for many reasons: from low-quality oil or oil clogged with impurities to a poor-quality crankshaft. A worn valve rocker makes a loud knocking sound (more like clicking).

A loud metallic knock indicates that there is no oil lubrication between the contacting parts.

Thud

A dull, low knocking sound at the bottom of the crankcase indicates the need to replace the main bearings. If it increases significantly with increased crankshaft rotation, the problem is 90% related to them. Another sign of such wear is a drop in oil pressure. The crankshaft itself (its main journals) can make similar sounds - when the engine is running warm, they can be heard in the cabin on the left.

The dull nature of the knocking sound indicates that parts are hitting, one of which is made of soft metal, and there is a layer of lubricant between them.

Engine knocking when you press the gas

A knock in the engine when changing the number of revolutions (pressing or releasing the accelerator pedal) occurs for a number of reasons. It can be a dull or ringing knock, single or rhythmic. What all options have in common is that there is no noise at high speeds, only when the car needs to start or pick up speed. A knocking sound in the engine when revving up can also occur due to wear on the engine mount. But in 90% of cases, if the sound occurs only when the driver begins to press the gas, disappearing later (and does not affect the engine power), the reason is poor gasoline and detonation.

What sound could it be?

The noise can be constant or periodic (appearing during maneuvers, picking up speed, or immediately when turning on the car), and can be of different frequencies and tones.

As a rule, the appearance of a knock when the crankshaft accelerates is one of the most common phenomena.
And the faster the revolutions are made, the higher the sound frequency.
The tonality of the sound and its strength increase with friction, inconsistencies in the crank or GR mechanism.

Motor lubrication also plays an important role in the propagation of sounds. When the engine is hot, it will lose its thickness and increase the sound from the engine.

Engine knock in VAZ 2114

Car owners, especially those who do not have much experience, often complain about the knocking of a cold engine in a VAZ 2114. This includes new cars that have not driven even 50 thousand km. There is no need to be afraid of this; it is related to the technical features of the model. The design of the piston clearances was designed many years ago (then the task was to maximize the piston stroke) and remained practically unchanged. The high noise level is due to the height of the knee. If your car is under warranty, you can contact an official AvtoVAZ representative.

What are the consequences?

Any extraneous sounds from the engine are the result of significant wear of any car parts. Loosening of the fastening of a part, assembly or assembly may indicate the appearance of a gap.

In such cases, it is advisable to take your car to a good car dealership, where it will receive high-quality diagnostics and specialized assistance.

Knock on Lada Vesta

A common cause of knocking in the Lada Vesta on the right front part of the car is a design feature of the right engine mount. This does not affect driving performance; you can get rid of extraneous sound by lubricating the engine mount with silicone grease (except WD-40). It is applied there, the metal comes into contact with the rubber. You can install plates 1-2 mm thick into the support.

Knock of the pillow The pillow (support) of the engine is the part that fixes it. It prevents movement and dampens vibrations from the motor. The number of such supports varies depending on the model. In Russian cars, problems with such gaskets are quite common. This does not affect driving performance, but is annoying for the driver. For a number of reasons, this is relevant for Lada Vesta.

The main signs of support malfunctions:

Increased vibration of the steering wheel when the engine is running.
Knock in the gearbox area when driving on poor quality roads.
Excessive jerking in the transmission when driving or changing gears at high speed.
Knocking noise under the hood when driving on poor roads and idling.

To determine if the airbag is knocking, just drive off with the hood open. If the engine moves and a characteristic sound is heard, similar to the knocking of a faulty shock absorber, the cushion must be changed. With the engine turned off, you can try to move it by inserting a pry bar between the engine and the body.

The condition of the lower cushions must be determined by driving the car into an inspection pit.

Diagnostics

Engine knocking at idle speed is quite easy to diagnose. It is enough to listen to the engine with a stethoscope. This way you can accurately determine the source of the sound, and then carry out work to determine the cause of the malfunction and eliminate it. It is advisable to listen to the engine in different operating modes. After all, different knocks manifest themselves differently at different speeds. This will also allow you to more accurately identify the problem.

Read more about “How to make a car stethoscope with your own hands.”

Engine knocking in Kia Sportage 3

Like the IX35, the Sportage 3 has a G4KD engine. In addition to the problems described above, this engine has increased demands on oil. Due to savings on materials, which the manufacturer is famous for (in this engine, the plant saved on cooling nozzles), the pistons experience excessive temperature load. To delay the appearance of noise as much as possible, you need to change the oil more often, fill only certified oil (possibly with additives). It is possible to get rid of knocking completely only through a major overhaul.

Sounds from the internal combustion engine

At its core, knocking in the engine occurs at the moment when one part hits another part. If this sound did not haunt you when buying a car, a critical increase in the working gaps between the engine elements is probably to blame.

A knock may have a specific tone due to the material, and a change in this tone indicates changes in the characteristics of the material.
For example, the sound of soft parts that work with hard ones (liners, bearings) may change as the soft part wears out faster.

And if the problem is in the joint of the gas distribution mechanism, then the knocking will be the same for a long time, since such parts are made of durable material.

Let's sum it up

Above we talked about the main places where knocking can occur when you press the accelerator.

Since identifying the cause is quite difficult due to the large number of places where it can appear, you should start checking from the smaller ones.

First, check the interior and doors, then inspect the condition of the suspension and steering mechanism, and then diagnose the condition of the airbags.

It is better to check the transmission and drive last, since this may require removing them from the car.

Even if most of the places being checked are not the cause of the sound, an additional check of them will not hurt and will provide information about the condition of the car’s elements.

Source

Valve lifters and hydraulic compensators

There is both normal operation and breakdowns. Old engines were usually equipped with valve pushers; now hydraulic compensators are being installed more and more (what they are and what is better - I wrote here ). So here it is:

The old system takes into account the thermal gap (when cold) between the pusher and the camshaft cam. Therefore, after starting the engine, you can hear a characteristic knock, but it goes away after the metal heats up and this gap is removed. This is a completely normal operating mode designed by the engineers. True, due to long runs, the contact surfaces may wear out - a larger gap appears. And the noise may already appear when the engine is warm, then only adjusting the valves .

A more modern system (based on hydraulic compensators) ideally does not knock at all! This is because here the thermal gap is adjusted automatically and it is always minimal. However, if the noise begins to appear specifically from the valves, it means that the hydraulic compensators are either: - out of order, - dirty. You need to take it apart and look. SEPARATELY, I would like to highlight the engine oil, if you fill this system with oil of the wrong viscosity, knocking will also appear. THIS IS IMPORTANT HERE!

In any case, if it is constantly noisy both cold and hot, then you need to either adjust it or disassemble and clean (change if necessary) the expansion joints.

Cooling system

The cause of premature detonation may be exceeding the permissible engine temperature due to damage to the thermostat. With such a malfunction, coolant will not flow into the radiator in sufficient quantity, which will lead to engine overheating.

If the thermostat breaks down, it is also possible for excess coolant to enter the radiator, which leads to an increased noise level of its operation. This malfunction can be eliminated by cleaning the thermostat or replacing it.

Pistons - cylinder walls

Next comes heavy artillery. There is no longer a simple knock, and they are all caused by complex breakdowns. Or rather, wear and tear.

Pistons - usually the piston skirt wears out (the lower part, if exaggerated, it calms it down) and it begins to move a little from side to side, creating a knocking sound. Moreover, oil consumption increases and engine power decreases

The piston pin is the part that connects the connecting rod and the piston itself. If there is a gap in it (about 0.1 mm), then knocking noises appear

Cylinder block walls . Due to excessive wear, overheating, insufficient lubrication, or a damaged catalyst , they too can wear out. Scores may appear on the walls, play may form at the piston - and, of course, noise. There is no escape from this.

A major overhaul of the engine can fix all this; simple methods are not enough.