Timing 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. At the intake stroke, the timing opens the intake valve, so that air and gasoline 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.
The main components of the timing
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 timely opening and closing of valves. It is made of steel or cast iron, and is installed in the cylinder block or crankcase. 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, have an effect through the pushers on the valve. Each valve has its own pusher and cam.
Intake and exhaust valves are necessary to supply the air-fuel mixture to the combustion chamber and to remove exhaust gases. The inlet valves are made of chrome-plated steel, and the exhaust valves are made of heat-resistant steel. The valve has a rod on which the plate is mounted. Typically, inlet and outlet valves differ in plate diameter. Also to the timing should include the rods and the drive.
Gas distribution device
It is worth a few more words to say about the arrangement of intake and exhaust valves. The valve stem has a cylindrical shape and a groove for installing the spring. The movement of the valves is possible only in one direction - to the bushings. In order for the engine oil not to get into the combustion chamber, put sealing caps made of oil-resistant rubber.
There is also such a unit as a timing drive. This is the transmission of rotation from the crankshaft to the camshaft. It is noteworthy that two turns of the crankshaft account for one distribution. Actually, this is the duty cycle during 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 one camshaft, 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.
Gas distribution mechanism
The principle of operation on all motors, when it comes to types such as ICE, is almost the same. All work can be divided into 4 stages:
- fuel injection;
- compression;
- duty cycle;
- exhaust gas removal.
The supply of fuel to the combustion chamber is due to the movement of the crankshaft from top dead center (TDC) to bottom dead center (BDC). At the beginning of the movement of the piston, the intake valves open, and the fuel-air mixture is fed into the combustion chamber. After that, the valve closes, the crankshaft rotates 180 degrees from its original position during this time.
After the piston reaches the BDC, it rises. Therefore, the compression phase begins. When TDC is reached, the phase is considered complete. The crankshaft at this time rotates 360 degrees from its initial position.
Stroke and gas removal
When the piston reaches TDC, ignition of the working mixture from spark plugs occurs. At this time, the maximum compression moment is reached and high pressure is exerted on the piston, which begins to move to bottom dead center. When the piston is lowered, the stroke can be considered complete.
The final phase is the removal of exhaust gases from the combustion chamber. When the piston reaches the BDC and begins its movement towards the TDC, the exhaust valve opens and the combustion chamber gets rid of the gases that were formed as a result of the combustion of the fuel-air mixture. Upon reaching the BDC piston, the phase of gas removal is considered to be completed. In this case, the crankshaft from its initial position is rotated by 720 degrees. To achieve maximum accuracy, synchronization of the engine timing with the crankshaft is necessary.
The main malfunctions of the timing
The technical condition of the motor depends on how timely and efficiently the maintenance of the motor is 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 claps in the exhaust system. In the process of operation of the internal combustion engine, carbon deposits are formed, which becomes the cause of a loose fit of the valve to the seat. Shells and sometimes through holes (burnout) appear on the valves. Compression also falls due to deformation of the cylinder head and a leaky gasket.
- A noticeable drop in power and traction, extraneous metal knocks and treble. The main reason is the incomplete opening of the intake valves as a result of the 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 considered normal. Depending on the frequency and quality of ICE service, signs of critical wear on one type of power unit can occur at different mileage.
- Worn timing chain or belt. The chain is stretched and can jump or even break. This also applies to a belt whose service life is limited not only by mileage, but also by time.
How is the timing diagnosis performed?
The gas distribution mechanism of a VAZ or any other machine works according to one principle. Therefore, the diagnostic methods and the main malfunctions are usually the same. The main failures are incomplete opening of valves and loose fit to the sockets.
If the valve does not close, pops appear in the intake and exhaust manifolds, and also thrust and engine power are reduced. This happens due to deposits on the seats and valves, as well as due to the loss of spring elasticity.
Diagnosis is quite simple. The first step is to check the valve timing. Then measure the thermal gaps between the beam and the valve. In addition, the clearance between the seat and 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 small goniometer, momentoscope, pointer, etc. The procedure is performed on a drowned engine. The goniometer is mounted on the crankshaft pulley. The valve opening period is always checked in the 1st cylinder. To do this, manually crank the crankshaft until a gap appears between the valve and the beam. Using a small protractor on the pulley determine the clearance and draw conclusions.
The simplest but least accurate method of measuring the thermal gap is carried out using a set of plates with a length of 100 mm and a maximum thickness of 0.5 mm. 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 result. Indeed, the permissible error is often too large. In addition, if there is uneven wear on the rocker arm and rod, then the data obtained can generally not be taken into account.
Timing Service
As practice shows, most of the breakdowns of the gas distribution mechanism is 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 breaks, the timing marks go astray, 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 of the coolant for its circulation through the system. Destruction of the impeller or failure of the gasket leads to serious problems with the engine. The casters and tensioner must also be replaced. Any bearing sooner or later fails. If the rollers and the tensioner itself are changed in a timely manner, then the chance to encounter such a problem is minimal. Jamming the roller very often leads to a break in the 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 is broken at medium and high speeds, engine overhaul is required. Almost always, a cylinder-piston group is subject to replacement. But even during normal use, parts are subject to wear. The first thing that affects the neck, cams, and also significantly increase the clearance in the bearings of the crankshaft. All work is carried out only by specialists using high-precision equipment. All grooves are made for repair dimensions, which are laid by the manufacturer. Usually 2 overhauls are provided, after which the engine must be changed to a similar one.
Some tag info
As already noted above, timing is a complex and extremely responsible unit. If the timing gear is not synchronized, then starting the car will not work. The main reason for the desync is bad labels. The belt or chain may become loose due to failure of the tensioner or natural wear. Marks are set relative to the crankshaft. To do this, the pulley is removed, which will allow us to see the gear, it has a mark on it that must coincide with the mark on the oil pump or unit. Corresponding marks are also available on 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 over one tooth is not a big deal, the motor will work, but with deviations. If the label goes into several divisions, then it will be impossible to start a 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 site that should be serviced regularly. But it is important to consider the quality of spare parts. After all, it is from them that the life of the timing often depends. The qualified installation of the original components of the gas distribution system almost completely guarantees uninterrupted operation of the unit during the period until the scheduled maintenance. As for third-party manufacturers, there are no guarantees, especially when it comes to components from China of mediocre quality.
To summarize
For the node to work properly, it must be serviced on time. It should be understood that the more complex the engine, the more expensive the timing kit will cost. But saving is definitely not worth it. After all, the avaricious pays twice. Therefore, it is better to buy expensive spare parts once and sleep peacefully. Replacing a water pump in the event of a malfunction can be equated to a complete replacement of the mechanism. Not every engine design allows you to make such mistakes, because it will cost decent money. On some power units, a broken belt does not lead to kapitalka, but you should not count on this.