Modern cars of domestic and imported production are equipped with reliable, productive, wear-resistant power units. But any motors have a certain resource, the main elements and components of engines wear out with intensive use. Over time, any power unit is subject to major overhaul, the cost of which depends on the brand and model of machinery.
The need for maintenance and repair can be determined by several visual signs:
- the owner can hear an uncharacteristic knock, which the power unit emits during operation, from the exhaust pipe
- appears thick, black smoke;
- gradually increases the consumption of engine oil, fuel, reduced power, deteriorating dynamics;
- motor knocking is the most worrying.
A serviceable power unit works without any noise, so the appearance of knocks indicates the need to contact a service center.
Knocks in the power unit are caused by metal elements hitting each other. In the places of contact of components there are high loads, so the rapid wear of parts is the biggest problem. The more intense the knocking, the faster the components become unusable and the motor fails. If no action is taken at the first appearance of foreign noises, subsequent repairs will be costly.
Extraneous noises also occur when the gaps between the working elements of the unit increase. The tonality of the sound when a faulty motor is running changes greatly. It is enough for an experienced specialist to listen to the noise of the power unit to understand what the cause may be. If the necessary measures are not taken in time, the knock will progress, its tonality depends on the materials of the contacting parts.
If the cause of extraneous noises is the wear of timing components, the knocking remains constant for a long time. Changes in its tone and intensity indicate wear of parts made of high-strength alloys, as well as the imminent failure of the timing gear. If the soft parts of the power unit are worn out, for example, connecting rod and main liners, camshaft bearings, the engine knock quickly manifests itself and also intensifies intensively.
For any owner, the appearance of extraneous motor noises is always a nuisance, additional maintenance and repair costs. In order to avoid big problems, it is necessary to promptly visit the service center. Determining the cause of knocking on your own is quite difficult, since the source of noises can be various units and elements. The engine can knock bearings, connecting rods, attachments and other elements.
How to determine the cause of knocking independently
Masters of the service center when diagnosing the knocking of the power unit use modern equipment. Most often, possible causes are determined by the tone of the noise, gradually localizing the place of its appearance. Many specialists use a special stethoscope.
Every vehicle owner can use a simple device, with the help of which it is possible to independently determine the cause of knocking with high accuracy. This will require an empty tin can, which is attached to a piece of rebar. The metal bar is applied to different parts of the running motor, the sound is amplified by the can attached to the ear.
On different power units, the tonality of extraneous noises is not always a determining criterion. For motors with a volume of 1.4 liters and 3 liters, knocks and extraneous sounds can be of different intensity and loudness.
Determining the cause of knocking of the power unit:
- the intensity of the extraneous noise and its tone is influenced by the make and model of the motor, with the same malfunction, the knocks on different engines can be very different;
- the character of extraneous noises can be of three types: constant repetitive knocking, sounds of a certain frequency or appearing sporadically;
- in most cases, the volume and intensity depends on the operation of the engine, crankshaft speed and the current load;
- depending on the mode of operation of the engine changes the tone of extraneous noises on the faulty power unit.
With increasing engine shaft speed, the noise in most cases increases, which is determined by the increase in the load on the moving elements of the timing and crank mechanism. At idle speed, extraneous noises may disappear altogether or manifest themselves sporadically. Therefore, involvement in the diagnosis of a competent specialist is the best option for finding the cause of the defect. At the initial stage, periodically manifested extraneous sounds can be heard with the help of special equipment.
Technical examination of the motor is carried out with an increase in the revolutions of the power unit, respectively, the oil pressure in the internal combustion engine also increases. As a result, the extraneous noise can become weaker or completely disappear, even if the load on the power unit consistently increases.
Another peculiarity of knock diagnostics is the change of internal combustion engine temperature. When the engine warms up, the oil liquefies, the extraneous noise increases. On a cold motor, the sound can be practically absent. Also not uncommon reverse situations, the engine knocks at startup, after warming up the extraneous sound disappears. Trying to determine the cause of the knock, it is necessary to take into account all the above factors. To reliably identify the causes, it is necessary to have a lot of experience and skills, so it is best to contact a service center.
Causes of cold engine knocking
For many vehicle owners, the first signs of a defect in the powertrain are manifested in the form of knocks when starting a cold engine. After the engine warms up, extraneous noises disappear. It is possible to use the car in such cases, but at the first opportunity it is best to visit a service center. With intensive use of the motor, the main parts wear out, the gaps between them increase. After warming up, the elements expand, respectively, the gaps decrease and the knock disappears.
The most common cause of knocking of an unheated engine is wear of the piston group. The main factors that determine extraneous noises are:
with intensive operation of the motor, the liners at the cylinders wear out, the gap between the piston and the wall increases, exceeding the maximum allowable values guarantees the presence of a knocking motor;
aluminum alloys with high heat capacity are used for manufacturing cylinders; when heated, the metal expands, and in the cold state it is strongly compressed;
a warmed motor stops generating knocking, as the gap between the cylinder and the piston narrows and enters the limits defined by the manufacturer.
In addition to knocking in the piston group, a similar effect may be present in the timing gear. If there is a hydraulic chain tensioning system, oil is supplied to the main parts. In a cold power unit, lubricant does not enter the circuit immediately after starting the engine, foreign metallic sounds occur. For similar reasons, there are knocks at the level of hydrocompensators. If the sound does not disappear when the power unit warms up to the optimum temperature, the hydrocompensators are changed.
Causes of knocks of the warmed power unit
The need to contact the service center arises if the engine does not knock at startup, but as the power unit warms up, extraneous noises are clearly audible. First of all, an experienced technician will assume wear of the crankshaft or elements of the piston group. It is possible to understand the cause of knocking in more detail after studying the algorithm of engine operation:
- when starting the power unit, especially at low temperatures, the oil is thick and viscous, the available gaps are filled with lubricant, when rubbing parts extraneous noises do not manifest themselves;
- with increasing temperature inside the power unit liquefaction of lubricant occurs, with high wear of parts, knocking becomes clearly audible;
- extraneous sounds on a warmed engine occur when the gap between the crankshaft journals and the main liners in the bearings increases;
- similar situations are possible even when the crankshaft journals are slightly worn, when the clearance between the crankshaft journals and the crankpins in the bearings increases.
- crankpin and crankshaft journals, foreign noises do not disappear even as the engine warms up;
- cracks in the piston pin and skirt also result in a metallic hum when the engine is running.
The most common cause of rumbling is insufficient lubrication. If the rumble manifested itself on the road, you can top up the oil to the required level. In any case, after the end of the trip it is necessary to visit the service center. If such defects are detected, attention should be paid to the intensity of knocking. If the tone and frequency increase as the load increases while the vehicle is moving, the reason is the wear of the crankshaft bearings. If possible, it is necessary to stop operating the vehicle and call a tow truck to bring the equipment to service.
Many causes of knocking are due to the fact that the vehicle is filled with poor quality fuel. To eliminate extraneous noises, you can add an additive to the gas tank. As a result, the detonation characteristics of gasoline are improved. After this, it is recommended to refuel at a verified gas station.
Causes of knocking at idle engine speed
Cases in which the engine knocks at idle speed are quite common. In most situations, such a problem is not serious. With an increase in engine speed, the extraneous sound disappears. In this case, it is necessary to determine the cause, for this it is enough to undergo diagnostics in a specialized service. Extraneous sounds at idle are fixed for the following reasons:
- touching of the pump or generator pulley with the motor housing due to vibrations during operation;
- engine protection or timing cover is not well fixed, one or more fasteners may be loose;
- if the powertrain has a pinion gear, there is play in the pinion gears;
- the crankshaft pulley is loose.
The most difficult defect is the appearance of one or more cracks in the flywheel. Such breakdowns are fixed on cars equipped with an automatic transmission. For mechanical boxes, such a defect is unlikely, since the flywheel has a massive, solid construction. At idle, extraneous sounds can occur when loosening the fastening of the sprocket or crankshaft pinion. An experienced specialist can quickly determine the causes of knocking with great reliability.
What to do if the pistons knock
The wear of the parts of the powertrain is a consequence of intensive operation. As a result, the gap between the cylinder and the piston increases. When the gap grows to 0.3-0.4 mm, a strong knock may occur. When contacting the service center, the master will offer options for solving the problem. In addition to wear, the causes of noises are the lack of timely maintenance and improper operation. Overheating negatively affects the condition of the cylinder-piston group.
If the emerging knock resembles tapping on the clayware, the cause of the defect is in the cylinder block. In addition to tapping, the problem can be localized by the presence of light clicks. The knock makes itself known on the power unit, just started or running at low speeds. As the engine warms up, the pistons expand, respectively, the extraneous noise gradually disappears.
Causes of piston pin knocking
A pronounced metallic knock most often indicates wear of the piston pins. A ringing and subtle sound is clearly audible when the driver sharply presses or releases the accelerator pedal. Extraneous noises are fixed in the area of the cylinder block, occur when the gap increases to 0.1 mm.
Determine the source of the ringing knock can be determined independently, this requires unscrewing the spark plug. The absence of a spark plug stops the process of combustion of fuel in the cylinder, respectively, loads on the piston and knocking is absent. By alternately unscrewing the plugs you can identify the cylinder with increased clearances. Other possible causes of metal ringing can be the use of poor quality fuel, when the power unit experiences detonation. If you move uphill with a heavy load and in an overdrive gear, the powertrain also begins to knock.
Causes of extraneous crankshaft liner noises
In some cases, vehicle owners pay attention to extraneous noises in the area of the crankcase of the power unit. Muffled metallic knocking can be caused by the wear of the main bearings of the crankshaft. With a sharp press on the accelerator pedal, accompanied by an increase in revolutions, the knock increases. The same effect is recorded when driving at low speeds, abrupt throttle reset, use of low-quality lubricant.
Knocks in the area of the crankshaft can not be ignored, it is necessary to immediately contact a service center. The use of poor quality oil or consumables that do not meet the manufacturer’s tolerances are the most common causes of crankshaft problems. The first step is to change the lubricant. If the result is negative, it may be necessary to repair the motor.
Causes of knocking connecting rod liners
High tonality, distinctiveness and audibility characterize the knocking of connecting rod liners. The defect occurs when these elements are worn out due to intensive use. The consequences of extraneous sounds in the crank mechanism can be very serious. Operation of the vehicle in such situations is prohibited. It is best to take the car to a tow truck for service.
If the suddenly appeared knock begins to progress rapidly, becoming more pronounced with increasing crankshaft speed, it is desirable to stop operating the vehicle. The best option is to shut down and do not start the engine again. In a professional service, the engine is dismantled and overhauled.
Drivers who do not listen to the recommendations of experienced engineers, bring the crankshaft to complete degradation. Repair of the node becomes impossible, only its replacement with a similar part is suitable. With further operation of the car, the connecting rod cap is torn off, followed by penetration of the cylinder head. Repair such a motor is too expensive, it is cheaper to replace it.
You can hear the knock of the connecting rod rack yourself. A sharp, metallic ringing is best manifested when opening the throttle. At the same time, the engine oil pressure drops. In the absence of lubrication, the crankshaft jams after a maximum of 15 minutes, in most cases earlier. Such an engine needs to be replaced or repaired at high cost.
Root journals of the crankshaft can knock for two reasons. Extraneous sound of low tonality, corresponding to the vibration of the motor, is manifested by severe wear of the main journals. In such cases, the clearance between the cylinder block supports and crankshaft journals increases significantly.
Low oil pressure in the system is another reason for the knocking of the main journals. The consequence of such a problem is the formation of scoring on the metal elements. But even with such consequences, it is possible to continue operating the technique for some time. But it is best to immediately contact a service center and give the car for repair.
Extraneous sounds in the gas distribution mechanism
Valve knocking is the most unpleasant phenomenon, which can be heard by any car owner. Extraneous metallic sounds can occur in power units of different design, for example, with hydrocompensators in a set or with mechanical valves. For motors with hydrocompensators, the cause can be their wear. As a result, the mechanism ceases to withstand oil pressure. First of all, you should dismantle and wash the hydrocompensator. If this does not help, it is best to replace the hydraulic tappets with similar devices.
In power units with a valve drive of the mechanical type, the appearance of knocking is also possible. To eliminate extraneous noise, the valves are adjusted. For cars made by AvtoVAZ, a set of special washers is used for adjustment. For other makes and models of machinery, the adjustment of the mechanism is performed in other ways.
Incorrect clearance in the valve mechanisms is not the only cause of knocking. Extraneous sounds can manifest themselves in the following cases:
- with a high degree of wear of the cam of the camshaft;
- if there is a large gap between the tappet seat and the mechanism itself;
- wear of one or more valves is a common cause of knocking;
- similar effects are recorded when the adjusting washer fails;
- Knocking in the timing mechanism causes wear of the timing belt and tensioners.
In any situation, if extraneous sounds appear, check the condition of the engine oil. If lubrication is insufficient, pressure drops, the knock will manifest itself in almost 100% of cases. With the normal volume and pressure of oil, the problem is localized. Collections in the fuel equipment, drive mechanisms, attachments are excluded one by one. After localization of the problem, the peculiarities of the knock are determined, its intensity is checked when increasing and decreasing the load. If the extraneous sound increases with increasing load, it is most likely necessary to diagnose the CPG and CMM.
One of the causes of pronounced knocking is a problem with the timing gear. In normal mode, the crankshaft and camshaft have a rotation speed that differs by a factor of 2. If the knocking frequency is identical to the crankshaft rotation, the cause is in the timing gear. After starting the power unit, extraneous noise can be almost imperceptible, with an increase in temperature, the volume increases. The reason is the increase in valve clearances due to thermal expansion. When the load increases, the knock may remain unchanged, as it does not depend on the operating mode of the unit.
Full diagnostics of the motor should be performed at the first symptoms of a power unit malfunction. Appeal to professionals is an opportunity to identify the problem without errors and determine ways of its elimination. In complicated cases it will be necessary to dismantle the power unit, disassemble it, defect analysis and replacement of damaged elements. In the best case, partial disassembly of the motor will be required.
To prolong the life of the power unit without defects and breakdowns, it is necessary to perform regular diagnostics and maintenance. For gasoline cars, the periodicity of replacement of consumables is 10-15 thousand kilometers. Diesel engines need to be serviced every 7.5-10 thousand. When operating machinery in harsh conditions, the frequency of maintenance is negotiated individually.
Total table
| Knock type | Possible Causes | Treatment options |
|---|---|---|
| Knocking when starting a cold engine | Wear of piston group, increased clearances between piston and cylinder | Repair or replacement of the piston group, diagnosis of hydrocompensators |
| Knocking when warming up the engine | Crankshaft wear, wear of main liners, cracks in the piston pin | Crankshaft liners replacement, crankshaft repair |
| Knocking when revs rise | Crankshaft or connecting rod bearing wear, timing problems | Bearing repair or replacement, timing system diagnosis |
| Knocking at idle | Loosen fasteners of engine components (pump, alternator pulley), timing wear | Diagnostics of fasteners, tightening of bolts, check of timing system condition |
| Metallic ringing knock when over throttle | Wear of piston pins, detonation due to low-quality fuel | Replacement of piston pins, use of quality fuel |
| Knocking in the area of the crankcase | Wear of main bearings, low oil pressure, use of poor quality lubricant | Change bearings, check oil level and quality |
| Valve knocking | Wear of hydrocompensators, improper valve adjustment | Replacing or adjusting valves, flushing or replacing hydrocompensators |
| Knocking in the timing mechanism | Wear of the timing belt, rollers, chain tension failure | Replacement of the belt/chain, rollers, tensioners |
| Knocking of connecting rods | Wear of connecting rod liners, loosening of connecting rod fasteners | Replacement of connecting rod liners, engine overhaul |
| Piston knocking (tapping on a clay dish) | Cylinder block wear, clicking at low revs | Cylinder block diagnostics, engine overhaul |
Anti leaders in the rating of motors
Modern motors are inferior in reliability to units released 10-15 years ago. One of the most unsuccessful is considered to be the engine for Volkswagen Polo with a volume of 1.6 liters. All three modifications, produced since 2010, were equipped with a chain drive. There is no phase change system in the motors.
Many owners of cars of this brand notice the knocking of pistons at the time of starting and warming up the engine. Despite the unpleasant sounds, such noises do not have a negative impact on the condition of the engine. After warming up to operating temperature, the knocking stops. Another problem of power units is the knocking of hydrocompensators, but such situations are recorded very rarely.
Diesel motors DCi for Renault also have characteristic defects. Motors with a volume of 1.5 to 2.2 liters, manufactured in the period from 2001 to 2009 are not distinguished by reliability and wear resistance. The most problematic unit is the crank mechanism. With severe overheating and heavy load, the motor begins to knock. First of all, the engine oil is changed. For power units with a capacity of 1.5 liters, the rotation of connecting rod liners is possible after 130 thousand kilometers of mileage.
Gasoline motors exceed diesel analogues in their reliability and wear resistance characteristics. In such engines, the crank mechanism practically does not cause problems. The breakdown of the crankshaft is fixed with oil starvation. The use of poor-quality lubricant also leads to the appearance of knocking.