Hydraulic lifters: what they are and why they knock


An internal combustion engine is the most complex unit in a car, the efficiency of which depends on the fine tuning of each mechanism associated with it. An example of this is the design of the gas distribution mechanism. It opens the intake and exhaust valves when the piston moving in the cylinder completes the corresponding stroke.

Everyone knows that during the operation of the internal combustion engine, all its parts heat up. At the same time, metal products expand. And when the motor is running, many processes in it are performed in a matter of fractions of a second. In this case, every micron of the gaps plays a role. If the valve opens a little earlier or later, this will significantly affect the efficiency of the power unit.

Hydraulic lifters: what they are and why they knock

For this purpose, in old motors, gaps were set between the valve tappet and the timing shaft cam. In modern motors, this process is simplified as much as possible. To be precise, the need for this has disappeared, since engineers have developed such a part as a hydraulic compensator.

What can a hydraulic lifter

The hydraulic expansion joint is installed between the valve tappet and the camshaft cam. This part independently adjusts the size of the thermal gap. As the name implies, automatic adjustment occurs due to the hydraulic action of oil on the expansion joint elements.

If earlier this function was performed by mechanical devices that constantly needed adjustment or replacement, these elements work in automatic mode, making life easier for the car owner.

A bit of history

In old engines, for example, the Soviet classics, there were no hydraulic or mechanical expansion joints for the thermal gap. For this reason, the routine maintenance of the vehicle included the mandatory adjustment of this parameter. Manufacturers often set an interval of 10 thousand kilometers.

Hydraulic lifters: what they are and why they knock

When this procedure was performed, the valve cover was removed and the value of the thermal gap was adjusted with a special probe and key. Not every owner could independently perform this procedure, and if this was not done, the engine began to run noisily and lose its dynamic properties.

In such engines, the valves had to be changed every 40-50 thousand run, which added headaches to the owners of such cars. The design needed to be improved, so a washer of a certain thickness began to be installed between the pusher and the cam. Now it was not the valve stem itself that was wearing out, but this part.

Despite this, the adjustment still had to be made, and the repair work was reduced to a simple replacement of the washer. Some manufacturers still use similar parts in their car engines.

Hydraulic lifters: what they are and why they knock

Despite the significant improvement in the operation of the gas distribution mechanism, the maintenance of the unit still had to be carried out quite often.

Mechanical expansion joints were replaced by an original mechanism that corrected the gaps automatically. The system of hydraulic compensators has increased the interval of maintenance work on the internal combustion engine almost three times, and now you need to look under the valve cover much less often - no more than 120 thousand kilometers.

The principle of operation of the hydraulic compensator

The hydraulic compensator has the following device:

  • A metal case in which all the elements of the mechanism are installed;
  • Plunger pair (for more details about the principle of operation of this element, read on the example of a plunger pair of a high-pressure fuel pump), which is powered by oil pressure;
  • Ball - serves as a check valve;
  • Spring - Allows the plunger valve to move into place when the part is at rest.
Hydraulic lifters: what they are and why they knock

The hydraulic compensator operates in the following two modes:

  1. The cam of the camshaft is turned away from the working surface of the compensator. There is no pressure on the plunger spring, so it raises it so that it is pressed against the cam. The plunger is filled with oil. The fluid pressure is equal to the pressure in the engine lubrication system;
  2. When the cam rotates towards the valve, it moves the plunger, lowering it towards the valve stem. The spring rate is selected so that the valve in the cylinder head opens in accordance with the cam position with minimal effort. To increase pressure on the valve stem, the volume of oil in the sub-piston space is used.

Thus, the hydraulic compensator "adjusts" not only to the thermal expansion of the timing parts, but also to the wear of the cams and valve stems. Such an original solution excludes frequent adjustment of the mechanism for these changes.

Briefly about the operation of the hydraulic compensator is described in this video:

Hydraulic compensators. How do hydraulic lifters work and why do they knock?

What are the types and types of hydraulic compensators

The principle of operation of one of the types of expansion joints was described above. Engineers from each individual car company can use other types of hydraulic lifters:

  • Hydraulic pusher as described above. It is installed between the camshaft cam and the valve stem;
  • Hydro support;
  • In old motors, a hydraulic support was used, which was installed in the rocker arms or in the levers of the valve tappets;
  • Roller hydraulic pushers.

Most car manufacturers are trying to get away from hydraulic supports, since the device of hydraulic pushers is as simple as possible. Although a device such as a gas distribution mechanism may not allow the use of this type of expansion joints. The photo below shows which location of the hydraulic lifter may be depending on the type of engine timing.

Hydraulic lifters: what they are and why they knock

Pros and cons of a hydraulic expansion joint

Hydraulic lifters have many advantages. These include:

  • Low noise of the motor;
  • No need to adjust the clearances of thermal and valves caused by natural wear;
  • Maintenance free;
  • Provides constant pressure of the valve stem against the camshaft cam, which ensures high efficiency even for a heavily worn gas distribution mechanism;
  • Stable dynamic characteristics of the old motor.

However, despite the abundance of advantages, advanced technology also has several major disadvantages:

  1. Hydraulic compensators use oil pressure, and the holes in them are so small that the thick grease will simply not physically get inside, especially if the system has not yet had time to warm up. For this reason, high-quality oil must be poured into the engine - most often synthetics. But a motor with a high mileage, on the contrary, needs a thicker lubricant - the O-rings are already a little worn out, so synthetics are not able to create a high-quality oil wedge. Because of this, the dynamics of the motor drops;
  2. Even if synthetics are used, the oil still needs to be changed more often, since over time it loses its fluidity;
  3. In case of failure, you will need to buy ideally the same part, and not a cheaper analogue (the location of the hydraulic compensator does not allow the use of a design other than that provided by the manufacturer);
  4. Since the breakdown occurs at later stages, the repair will cost more than with the planned maintenance of the internal combustion engine;
  5. Sometimes, due to poor quality lubrication, the plunger can become clogged, which will lead to incorrect operation of the mechanism.
Hydraulic lifters: what they are and why they knock

The biggest disadvantage is the exactingness of the oil quality. If a motorist ignores the requirements for this parameter, very soon he will have to fork out for the purchase of new expansion joints. In the case of motors that have developed a long resource, mechanical analogs will be a good alternative - they prevent valve wear and at the same time regulate the thermal gap.

How to choose hydraulic lifters

If the engine timing belt is equipped with hydraulic lifters, then the question of whether to buy new parts or not is not worth it - definitely buy. Otherwise, the phase distribution in the power unit will not work correctly - the cam will not be able to open the valve in time, and the motor will lose its efficiency.

If it is not known which models are installed in the motor, then the search for hydraulic lifters is carried out by the VIN code of the vehicle or by the motor model in the catalog. It is worth considering that some sellers call any expansion joints pushers. When selecting a part, you can also indicate to the seller the type of valve timing (SOHC or DOHC - read about the difference between such modifications here).

Hydraulic lifters: what they are and why they knock

When choosing a budget or original compensator, you should also pay attention to its technical characteristics - weight, spring rate, etc. (if they are listed in the catalog). If the valves have a small stroke, then lightweight expansion joints can be installed.

Which hydraulic lifters are better

When choosing this part, you should remember: a budget analogue often requires replacement. But even among the so-called original spare parts, a fake comes across. In order not to waste money on low-quality products, pay attention to manufacturers who have proven themselves in the auto parts market.

Also note that the auto manufacturers themselves do not manufacture hydraulic expansion joints. They use the services of individual companies, so this part does not exist from the manufacturer - they are purchased from independent companies and sold like the original, but at a higher price.

Hydraulic lifters: what they are and why they knock

You can stop your choice on the following manufacturers:

  • German manufacturer INA. Hydraulic compensators are of excellent quality and almost never fail ahead of schedule;
  • Another German company Febi, but the quality of their products is slightly lower than that of the previous representative. The country of manufacture is indicated on the packaging of the part - you should pay attention to this, since Chinese factories do not always manufacture premium products;
  • SWAG is a company whose services are used by the manufacturers of the VAG group (about which car brands are included in the concern, told a little earlier). Parts of this company are in the budget category, but counterfeiting is much more common;
  • Below in the ranking are the Spanish-made hydraulic lifters AE or Ajusa. The consequence of the relatively low cost is a small working resource (about 10 mileage). Another drawback is the high demands on the quality of the oil.

Diagnostics and replacement of hydraulic lifters

Malfunction of hydraulic lifters is diagnosed by knocking them. A phonendoscope is used to make sure that the characteristic sound comes from the compensators.

Hydraulic lifters: what they are and why they knock

If a malfunction of the hydraulic lifters is established, then they are dismantled with a magnet, but this is in the case of a clean and serviceable timing mechanism. It happens that the part sticks in the seat, which is why dismantling must be done with a special puller.

There are several ways to check the performance of the hydraulic lifter. First, an external examination of the part is carried out to find defects. The working surface of the element will be visible to the naked eye. Secondly, there are collapsible expansion joints. In this case, you can inspect the internal components to determine the degree of wear.

Hydraulic lifters: what they are and why they knock

Another diagnostic method - oil is poured into the dismantled expansion joint. A working part cannot be squeezed with your fingers. Otherwise, it should be replaced.

Why do hydraulic lifters knock

There are several reasons for the knock of expansion joints. Here are some of them:

Engine operating mode:Reason:How to solve:
"Cold"Thick oil (the cavity of the sub-plunger space fills slowly); Due to untimely oil change, clots or foreign particles have appeared in the cavities, blocking the operation of the plunger or spring; Natural wearChange the oil in a timely manner; Adhere to the manufacturer's recommendations for the choice of lubricant; In case of failure, the part changes (in order to perform this procedure less often, the entire set changes)
"Hot"Wedge in the plunger pair (most often due to wear of the contact surfaces, for example, the formation of scuffing); Poor lubrication quality (even heated oil does not lose its density or, on the contrary, is too liquid, so it appears through the technical gaps)Change the oil and the hydraulic lifters in time; Use only the type of lubricant specified by the manufacturer

To eliminate the knock of recently replaced expansion joints, flushing of the thin channels in the lubrication system will be required. To do this, you can use special tools, for example, Liqui Moly Hydro Stossel Additiv. It is added to the lubrication system of a car after the engine has warmed up. The effect of the remedy comes after 500 kilometers.

Such additives should not be used immediately or as a preventive measure, as the substance can increase the thickness of the oil, which can adversely affect the lubrication of the entire engine.

Hydraulic lifters: what they are and why they knock

If the lubrication system is heavily contaminated, before installing new expansion joints, it must be flushed with a special oil. In rare cases, it will be necessary to disassemble the power unit. For this reason, do not neglect the regulations for replacing the internal combustion engine lubricant. Read more about this in another review.

In conclusion, watch a video review on how to eliminate knocking hydraulic expansion joints:

WHAT IF hydraulic lifters are knocking in the engine. How to fix! Knocking lifters


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