Timing belt is one of the most critical and complex components in a car. The gas distribution mechanism controls the intake and exhaust valves of an internal combustion engine. On the intake stroke, the timing belt opens the intake valve, allowing air and gasoline to enter the combustion chamber. On the exhaust stroke, the exhaust valve opens and exhaust gases are removed. Let's take a closer look at the device, the principle of operation, typical breakdowns and much more.
Main timing units
The main element of the gas distribution mechanism is the camshaft. There may be several or one, depending on the design features of the internal combustion engine. The camshaft performs the timely opening and closing of the valves. It is made of steel or cast iron, and is installed in the cylinder block orcrankcase. From this we can conclude that there are several engine designs - with an upper and lower camshaft. There are cams on the shaft, which, when the camshaft rotates, act through the pushers on the valve. Each valve has its own tappet and cam.
Intake and exhaust valves are needed to supply the fuel-air mixture to the combustion chamber and remove exhaust gases. The intake valves are made of chrome-plated steel, and the exhaust valves are made of heat-resistant steel. The valve has a stem on which the plate is attached. Typically, intake and exhaust valves differ in the diameter of the plate. Also, the timing should include rods and drive.
It is worth a few more words to say about the design of the intake and exhaust valves. The valve stem has a cylindrical shape and a groove for mounting the spring. The movement of the valves is possible only in one direction - towards the bushings. To prevent engine oil from entering the combustion chamber, sealing caps made of oil-resistant rubber are installed.
There is also such a node as the timing drive. This is the transmission of rotation from the crankshaft to the camshaft. It is noteworthy that for two revolutions of the crankshaft there is one distribution. Actually, this is the duty cycle in which the valves open. It is worth noting that a motor with two camshafts is more powerful and has higher efficiency. This is especially noticeable at high speeds. For example, when an internal combustion engine is equipped with onecamshaft, then the marking looks like this: 1.6 liters and 8 valves. But two shafts - this is always twice as many valves, that is, 16. Well, now let's go further.
Operation of the gas distribution mechanism
The principle of operation on all motors, when it comes to types such as internal combustion engines, is almost the same. All work can be conditionally divided into 4 stages:
- fuel injection;
- duty cycle;
- exhaust gas removal.
Fuel is supplied to the combustion chamber by the movement of the crankshaft from top dead center (TDC) to bottom dead center (BDC). When the piston begins to move, the intake valves open, and the fuel-air mixture is fed into the combustion chamber. After that, the valve closes, during this time the crankshaft rotates 180 degrees from its original position.
After the piston reaches BDC, it rises. Hence, the compression phase begins. When TDC is reached, the phase is considered completed. The crankshaft at this time rotates 360 degrees from its initial position.
stroke and venting
When the piston reaches TDC, the fuel mixture is ignited by the spark plugs. At this time, the maximum compression torque is reached and high pressure is applied to the piston, which begins to move towards bottom dead center. When the piston descends, the working stroke can be considered completed.
Final phase - removal of exhaust gases fromcombustion chambers. When the piston has reached BDC and begins its movement towards TDC, the exhaust valve opens and the combustion chamber is rid of the gases that were formed as a result of the combustion of the fuel-air mixture. When the BDC piston is reached, the gas removal phase is considered to be completed. In this case, the crankshaft rotates 720 degrees from its initial position. To achieve maximum accuracy, the timing mechanism of the engine must be synchronized with the crankshaft.
Main Timing Malfunctions
The technical condition of the motor depends on how timely and efficiently the maintenance of the motor will be carried out. During operation, all elements are subject to wear. This also applies to timing. The main malfunctions of the mechanism are as follows:
- Low compression and pops in the exhaust system. During the operation of the internal combustion engine, carbon deposits form, which causes a loose fit of the valve to the seat. Shells appear on the valves, and sometimes through holes (burnout). Also, compression drops due to deformation of the cylinder head and a leaky gasket.
- Noticeable drop in power and traction, extraneous metallic knocks and tripping. The main reason is the incomplete opening of the intake valves as a result of a large thermal gap. Part of the air-fuel mixture does not enter the combustion chamber. This is due to the failure of the hydraulic lifters.
- Mechanical wear of parts. Occurs during engine operation and is considereda normal occurrence. Depending on the frequency and quality of maintenance of the internal combustion engine, signs of critical wear on one type of power unit may appear at different mileage.
- Worn timing chain or belt. The chain is stretched and may jump or even break. This also applies to the belt, the service life of which is limited not only by mileage, but also by time.
How is timing diagnostics performed?
The gas distribution mechanism of a VAZ or any other car works on the same principle. Therefore, the diagnostic methods and the main malfunctions are usually the same. The main breakdowns are incomplete opening of the valves and loose fit to the sockets.
If the valve does not close, pops appear in the intake and exhaust manifolds, as well as reduced thrust and engine power. This happens due to carbon deposits on the sockets and valves, as well as due to loss of elasticity of the springs.
Diagnosis is quite simple. The first step is to check the valve timing. Next, measure the thermal gaps between the rocker arm and the valve. In addition, the clearance between the seat and the valve is checked. If we talk about the mechanical wear of parts, then most of the breakdowns are associated with critical wear of the gears, as a result of which the belt or chain does not fit snugly against the tooth and slippage is possible.
Timing phases and thermal clearance
It is quite difficult to independently diagnose the state of the phases of the gas distribution mechanism. To do this, you need a set of tools such as a goniometer, a momentoscope,pointer, etc. The procedure is performed with the engine turned off. Malka-protractor is installed on the crankshaft pulley. The valve opening period is always checked in the 1st cylinder. To do this, manually turn the crankshaft until a gap appears between the valve and the rocker arm. With the help of a goniometer, the gap is determined on the pulley and conclusions are drawn.
The simplest but least accurate method of measuring the thermal gap is with a set of plates 100mm long and 0.5mm maximum thickness. One of the cylinders on which measurements will be taken is selected. It must be brought to TDC by manually turning the crankshaft. Plates are inserted into the formed gap. The method does not give 100% accuracy and results. After all, the margin of error is often too large. In addition, if there is uneven wear of the rocker striker and rod, then the data obtained can generally be ignored.
As practice shows, most of the breakdowns of the gas distribution mechanism are associated with untimely maintenance. For example, the manufacturer recommends changing the belt every 120 thousand kilometers. The owner does not take into account these data and uses a belt of 200 thousand. As a result, the latter is torn, the timing marks are knocked off, the valves collide with the pistons and a major overhaul is required. The same applies to such an element of the mechanism as a water pump. It creates the necessary pressure for the coolant to circulate through the system. Destruction of the impeller or failure of the sealing gasket leads toserious engine problems. The rollers and tensioner must also be replaced. Any bearing fails sooner or later. If you change the rollers and the tensioner in a timely manner, then the chance of encountering such a problem is minimal. Jamming the roller very often leads to a broken belt. That is why it is necessary to perform timely maintenance of the gas distribution mechanism.
About timing repair
In most cases, when the timing breaks at medium and high speeds, an overhaul of the engine is required. Almost always, the cylinder-piston group is subject to replacement. But even under normal use, parts are subject to wear. First of all, the necks, cams suffer, and the clearances in the crankshaft bearings also increase significantly. All work is carried out only by specialists using high-precision equipment. All grooves are made to repair dimensions, which are laid down by the manufacturer. Usually, 2 overhauls are provided, after which the engine must be replaced with a similar one.
Some information about tags
As noted above, the timing is a complex and extremely responsible unit. If the timing drive is not synchronized, then the car will not start. The main reason for desynchronization is broken tags. A belt or chain may become loose due to tensioner failure or normal wear and tear. The marks are set relative to the crankshaft. To do this, the pulley is removed, which will allow us to see the gear, there is a mark on it, which must match the mark on the oil pump or block.Corresponding marks are also available on the camshafts. Using the instruction manual, set the timing marks. It is very important to understand that the result depends on the correctness of the work. A belt jumping one tooth is not scary, the motor will work, but with deviations. If the mark goes a few divisions, then it will be impossible to start the car.
Quality Spare Parts
We figured out what the purpose of the gas distribution mechanism is. You already know that this is a very responsible node that must be serviced regularly. But it is also important to consider the quality of spare parts. After all, it is on them that the service life of the timing belt often depends. A qualified installation of original components of the gas distribution system almost completely guarantees the uninterrupted operation of the unit during the period until scheduled maintenance. As for third-party manufacturers, there are no guarantees, especially when it comes to components from China of mediocre quality.
In order for the node to work properly, it must be serviced on time. It should be understood that the more complex the motor, the more expensive the timing kit will cost. But it's definitely not worth saving. After all, the miser pays twice. Therefore, it is better to buy expensive spare parts once and sleep peacefully. Replacing a water pump when it malfunctions can be equated to a complete replacement of the mechanism. Not every engine design allows you to make such mistakes,because it will cost a lot of money. On some power units, a broken belt does not lead to capital, but you should not count on it.