The main condition for the operation of an internal combustion engine is the presence of a gas distribution system. The people call the mechanism timing. This assembly must be regularly serviced, which is strictly regulated by the manufacturer. Failure to meet the deadlines for replacing the main components can entail not only repair of the timing, but also the engine as a whole.
Timing belt drive
Currently, there are two options for implementing the timing drive: belt and chain. The first is considered more common and easier to maintain. The system has several pulleys mounted on camshafts and crankshafts, as well as a water pump. The mechanism also includes a tension system and a bypass (stray) roller. Additional tensioners are needed in order for the belt to work strictly in its place without distortion. The rollers are, in fact, rolling bearings, which also need to be changed periodically.
It should be understood that timing belt repair is likethat is not being fulfilled. The latter is only subject to replacement. As for the scheduled timing for replacing the mechanism, it all depends on the manufacturer. In most cases, the timing belt is changed every 150 thousand kilometers, but in difficult operating conditions, which can be safely attributed to the mileage of the car across the territory of the Russian Federation, it is necessary to replace it every 90-100 thousand kilometers. Repair of the timing belt and other components is not recommended for the reason that the maintenance of the gas distribution mechanism is quite expensive, especially for V6 and V8 engines. Since repair work does not give any guarantees for the service life, it is possible to get an unscheduled replacement. Replacement kit: belt, idler and drive roller, water pump and oil seals.
About the chain drive
The main goal of engineers is to ensure the maximum resource of the car's power unit. And since a broken timing belt in most cases leads to fatal consequences, much attention was paid to the reliability of the assembly. In this regard, the chain drive was ahead of the belt drive. Almost always, a double-row chain drive is used, which engages with the corresponding sprockets mounted on the shafts (camshaft and crankshaft).
The main problem with chain is that it stretches over time. As a result of this, extraneous noise often appears and the timing marks are lost. Because of this, the engine loses some power and increases its wear. Repair of the timing chain, as well as the belt, is notperformed. The entire assembly is subject to replacement, starting from the sprockets and ending with the chain and damper with tensioner. As for the main advantages of a chain drive, this is its reliability and replacement intervals. It needs to be changed a little less often, approximately every 250 thousand kilometers. If this is not done on time, then an open timing chain may occur. Repair of the motor after such a breakdown will be quite expensive.
Regardless of the type of drive, the gas distribution mechanism works according to the same scheme. All work can be divided into 4 main stages:
- work stroke;
For this system to work properly and efficiently, it is necessary to synchronize the operation of the camshaft and crankshaft. Synchronous operation of the camshaft and crankshaft is the main task of the timing drive, regardless of its type and device.
The intake stroke starts with the movement of the crankshaft. It transfers force to the piston, which in turn starts moving from top dead center (TDC) to bottom dead center (BDC). At this time, the intake valves open and the fuel-air mixture enters the combustion chamber. After the valve is applied, it closes. The crankshaft rotates 180 degrees from its initial position during this cycle.
After the piston has reached BDC, it begins to rise to TDC. Consequently, the fuel-air mixture is compressed in the cylinder. The phase ends when the piston approaches top dead center. Crankshaft at the end of the strokerotated 360 degrees from its original position.
When the moment of maximum compression comes, the fuel mixture ignites, and the piston at this time, under the influence of the resulting gases, begins to move towards the BDC. When it reaches the bottom point, then the phase of the working stroke is considered to be completed. The removal of exhaust gases occurs during the subsequent movement of the piston to TDC and the opening of the exhaust valves. After the stroke is completed, the crankshaft rotates 720 degrees from its initial position.
The main elements of the gas distribution mechanism
GRM consists of a large number of parts, each of which performs the task assigned to it. The main element is the camshaft. In most cases, it is installed in the cylinder head. Modern engines are equipped with two camshafts, which increases the efficiency of the system as a whole and its reliability. In this case, the motor will have 16 valves, and with one camshaft - 8. When the shaft rotates, the valves are acted upon through cams mounted on cylindrical necks. The intermediate link between the cams and valves is the tappets.
Another important component is intake and exhaust valves. They are needed to supply the fuel-air mixture and remove exhaust gases. They are a rod with a plate. The rod is always cylindrical in shape with a selection for the spring. Valve movement is strictly limited. To prevent oil from entering the combustion chamber through the valves, the latter haveo-rings.
Another element is the timing drive. Rotation is transmitted through it. It should be understood that for 2 full revolutions of the crankshaft, the camshaft makes only one. That is, it rotates at half the speed.
Timing repair and maintenance
The denser the layout of components and assemblies under the hood, the more difficult it is to replace one or another part of the gas distribution mechanism. That is why scheduled repairs must be carried out completely, and not just change the belt or pump. After all, if the timing roller fails, the repair will cost a round sum, which can be equated to a full maintenance of the mechanism. As noted above, the manufacturer indicates a clear timeframe for replacing the gas distribution mechanism kit. They should try to keep up. Of course, initially the engineers laid a small margin of safety for the assembly. For example, nothing may happen to a belt or chain if it is replaced a little later. But it’s not worth delaying with this, because a break in most cases leads to the fact that the valves meet the pistons and bend them. For repairs, you will need to remove and disassemble the motor, and this is already a full-fledged capital.
It is advisable to service the timing from good specialists, although sometimes it is quite difficult to find them. The fact is that the configuration process includes labeling. If you do not synchronize the camshafts with the crankshaft, then the car will not start at all. It will be necessary to disassemble the assembly again, and do everything all over again. It is advisable not to change the shaft seals during the repair,which tend to leak.
Main Timing Malfunctions
Even if the timing gear is in good condition, this is not a guarantee of the normal operation of the unit. The fact is that during operation, soot and shells appear on the valves. Because of this, the valves do not fit tightly to the seats, and pops can be heard in the exhaust system, and compression is also slightly reduced. There are frequent cases of deformation of the cylinder head, a decrease in the gaps between the valves and seats, as well as jamming of the valve stem in the sleeve.
The second popular malfunction is a decrease in the power of the power unit. In most cases, the cause is incomplete closing of the intake valves. As a result, part of the fuel-air mixture does not enter the combustion chamber. The thermal gap increases, and hydraulic lifters fail. Usually the motor starts to triple, and extraneous knocks of a metallic nature appear.
Another typical problem is mechanical wear. It often happens that the timing belt just took and broke. Repair in this case will need unscheduled. What could be causing this? Everything is extremely simple - critical wear of gears or bearings. They loosen up or completely jam. But even in this case, the breakage often does not occur immediately. Yes, and changes in the operation of the engine is difficult not to notice. Therefore, it is advisable to eliminate rustling or whistling sounds in the area of the gas distribution mechanism immediately.
GRM: repair of Renault and otherscars
In most cases, the procedure for replacing the gas distribution mechanism on all cars is almost identical. We are talking about engines with an in-line arrangement of cylinders. If you have V6 and above, then it will be an order of magnitude more difficult to perform an independent replacement.
Let's take as an example a car "Renault Scenic" with a power unit of the K4M type. On it, many drivers recommend changing the timing at least every 80 thousand kilometers. If everything is more or less clear with disassembly, then when assembling the assembly, it is very important to correctly set the marks. To do this, you need to duplicate the marks from the old belt and it is advisable to start the installation from the camshaft. Further, the belt is thrown through the bypass and tension roller with a pump. If the phase regulator is removed, then, having thrown off the belt from the pump, it must be installed. For ease of installation, many drivers remove the crankshaft gear and install it last. Timing repair of a 16-valve engine has only the difference that it is necessary to synchronize two camshafts. This is easy to do, because each of them has the appropriate labels. Similarly, the replacement is carried out on VAZ cars, regardless of the motor. It is possible to independently carry out such repairs only with the presence of special tools and equipment. Although someone is able and "on the knee" to repair the drive.
Node repair process
Many people buy used cars. Almost all owners before selling say that the timing kitchanged very recently. Well, if this is true. After all, a cliff can lead to capital, which is usually about 20% of the cost of the car or even more. In order not to repair timing valves in the future, it is advisable to diagnose the assembly and make an appropriate decision. In most cases, it is not recommended to leave any part, replacing all the others. As mentioned above, failure of the water pump or roller will lead to repeated repairs. It's good if you can avoid breaking the belt.
There is such a type of work as "timing troubleshooting". The essence of the event is to identify problems in the operation of the gas distribution mechanism drive. In fact, the work includes inspecting the assembly and assessing the condition of the belts, rollers, water pump, etc. Also, when troubleshooting, the timing marks are checked and, if necessary, they are set. It must be understood that much depends on how qualified employees carried out the repair of the timing belt of the car. After all, if the mechanics at the service station are not familiar enough with the design and arrangement of the gas distribution mechanism of a particular car, then it is better to use the services of another service.
The right choice of spare parts
As practice shows, it most often causes a problem during the overhaul of the timing engine. And far from always it lies in untimely service. In some cases, it's all about the parts. The fact is that there are original belts, rollers and water pumps. The word "original" should be understood as those spare parts,which have been set by the manufacturer. In most cases, they have a fairly long life and a good margin of safety with proper operation and maintenance. For example, a water pump is designed for an average of 150,000 miles. Absolutely all parts can withstand such an interval, from bypass rollers to a belt or chain. But even with such a run approaching, the timing can work quite normally for another 30 or 50 thousand kilometers. But there is no longer any guarantee that it will not be cut off at the most inopportune moment. Nevertheless, a certain stock is still provided by the manufacturer.
Well, now the next situation. Original parts for most cars cost decent money. The only exceptions are some cars of the VAZ family. Repair of the Zhiguli timing belt is not a very expensive and complicated undertaking. Well, if there is a 5-liter monster under the hood, then buying original timing belts for it will cost more than one hundred dollars. It is quite natural that motorists want to save money by purchasing analogues of not the best quality. As a result, after 10-20 thousand kilometers, play appears in the bearings, the pump begins to leak, etc. In this case, the driver is forced to repeatedly change the timing parts, which leads to unjustified costs. In the worst case, you will have to perform work such as repairing timing valves, or rather, their complete replacement.
The gas distribution mechanism of an internal combustion engine requires regular and high-quality maintenance. In thatcase, you can be sure of its long-term trouble-free operation. Some engines are not afraid of a broken belt, and the valves do not bend. But even in this case, it is not pleasant enough, because finding a belt on the track is quite problematic.
Despite all of the above, there is no need to treat the timing as something special. The mechanism simply needs to be replaced at the scheduled time, which is indicated in the service book. Also, do not try to save on spare parts by installing cheap Chinese bearings and pumps of incomprehensible production. It is also advisable to monitor the condition of the protective cover of the mechanism, because often its damage leads to dirt and water getting on the rollers and belt, which helps to reduce the resource. If a breakdown has already happened, then you need to find specialists who can qualitatively repair the timing chain or belt.