For the stable operation of an internal combustion engine, each of its parts plays an important function. Among them is the camshaft. Consider what is its function, what faults occur, and in what cases it needs to be replaced.
Where is the camshaft located?
The location of the camshaft depends on the design features of the motor. In some modifications, it is located below, under the cylinder block. Modifications of engines are more common, the camshaft of which is located in the cylinder head (on top of the internal combustion engine). In the second case, the repair and adjustment of the gas distribution mechanism is much easier than in the first.
Modifications of V-shaped engines are equipped with a timing belt, which is located in the collapse of the cylinder block, and sometimes a separate block is equipped with its own gas distribution mechanism. The camshaft itself is fixed in the housing with bearings, which allows it to rotate continuously and smoothly. In boxer engines (or boxer), the design of the internal combustion engine does not allow the installation of one camshaft. In this case, each side has its own gas distribution mechanism, but their work is synchronized.
The camshaft is an element of the timing (gas distribution mechanism). It determines the order of the engine strokes and synchronizes the opening / closing of the valves, which supply the air-fuel mixture to the cylinders and remove the exhaust gases.
The gas distribution mechanism works according to the following principle. At the moment of starting the engine, the starter crank cranksth shaft... The camshaft is driven by a chain, a belt over a crankshaft pulley, or gears (in many older American cars). An intake valve in the cylinder opens and a mixture of gasoline and air enters the combustion chamber. At the same moment, the crankshaft sensor sends a pulse to the ignition coil. A discharge is generated in it, which goes to spark plug.
By the time the spark appears, both valves in the cylinder are closed and the fuel mixture is compressed. During a fire, energy is generated and the piston moves downward. This is how the crankshaft turns and drives the camshaft. At this moment, he opens the exhaust valve through which the gases exhausted during the combustion process are released.
The camshaft always opens the correct valve for a specific period of time and to a standard height. Thanks to its shape, this element ensures a stable cycle of the cycle of the cycle in the motor.
Details on the phases of opening and closing the valves, as well as their settings, are shown in this video:
Depending on the modification of the engine, one or more camshafts may be in it. In most cars, this part is located in the cylinder head. It is driven by the rotation of the crankshaft. These two elements are connected by a belt, timing chain or gear train.
Most often, one camshaft is equipped with an internal combustion engine with in-line cylinders. Most of these engines have two valves per cylinder (one inlet and one outlet). There are also modifications with three valves per cylinder (two for inlet, one for outlet). Engines with four valves per cylinder are more often equipped with two shafts. In opposed combustion engines and with a V-shape, two camshafts are also installed.
Motors with a single timing shaft have a simple design, which leads to a decrease in the cost of the unit during the manufacturing process. These modifications are easier to maintain. They are always installed on budget cars.
On more expensive engine modifications, some manufacturers install a second camshaft to reduce the load (compared to timing options with a single shaft) and in some ICE models to provide a shift in the gas distribution phases. Most often, such a system is found in cars that must be sporty.
The camshaft always opens the valve for a specific period of time. To improve the efficiency of the motor at higher rpm, this interval must be changed (the engine needs more air). But with the standard setting of the gas distribution mechanism, at increased crankshaft speeds, the intake valve closes before the required amount of air enters the chamber.
At the same time, if you install a sports camshaft (the cams open the intake valves for longer and to a different height), at low engine speeds, there is a high probability that the intake valve will open even before the exhaust valve closes. Because of this, some of the mixture will enter the exhaust system. The result is a loss of power at low speeds and an increase in emissions.
The simplest scheme to achieve this effect is to install a cranking camshaft at a certain angle relative to the crankshaft. This mechanism allows early and late closing / opening of the intake and exhaust valves. At rpm up to 3500, it will be in one position, and when this threshold is overcome, the shaft turns a little.
Each manufacturer equipping its cars with such a system indicates its own marking in the technical documentation. For example, Honda indicates VTEC or i-VTEC, Hyundai – CVVT, Fiat – MultiAir, Mazda – S-VT, BMW - VANOS, Audi - Valvelift, Volkswagen - VVT и др.
To date, in order to increase the performance of power units, electromagnetic and pneumatic camless gas distribution systems are being developed. While such modifications are very expensive to manufacture and maintain, so they are not yet installed on production cars.
In addition to the distribution of engine strokes, this part drives additional equipment (depending on the modification of the engine), for example, oil and fuel pumps, as well as the distributor shaft.
Camshafts are manufactured by forging, solid casting, hollow casting and more recently tubular modifications have appeared. The purpose of changing the technology of creation is to lighten the structure to obtain maximum efficiency of the motor.
The camshaft is made in the form of a rod, on which there are the following elements:
- Sock. This is the front of the shaft where the keyway is made. The timing pulley is installed here. In the case of a chain drive, an asterisk is installed in its place. This part is fixed from the end with a bolt.
- Oil seal neck. An oil seal is attached to it to prevent grease from leaking out of the mechanism.
- Support neck. The number of such elements depends on the length of the rod. Support bearings are mounted on them, which reduce the frictional force during the rotation of the rod. These elements are installed in the corresponding grooves in the cylinder head.
- Cams. These are protrusions in the form of a frozen drop. During rotation, they push the rod attached to the rocker arm (or the valve tappet itself). The number of cams depends on the number of valves. Their size and shape affects the height and duration of the valve opening. The sharper the tip, the faster the valve will close. Conversely, the shallow edge keeps the valve open a little. The thinner the cam shaft is, the lower the valve will go down, which will increase the volume of fuel and accelerate the removal of exhaust gases. The type of valve timing is determined by the shape of the cams (narrow - at low speeds, wide - at high speeds).
- Oil channels. A through hole is made inside the shaft through which oil is supplied to the cams (each has a small outlet). This prevents premature erasure of the push rods and wear on the cam planes.
If a single camshaft is used in the engine design, then the cams in it are located so that one set moves the intake valves, and a slightly offset set moves the exhaust valves. Engines with cylinders equipped with two inlet and two outlet valves have two camshafts. In this case, one opens the intake valves, and the other opens the exhaust gas outlet.
In engines with a carburetor, a distributor is connected to the camshaft, which determines which phase is performed in the first cylinder - intake or exhaust.
There is no distributor in the injection internal combustion engines, therefore, the camshaft position sensor is responsible for determining the phases of the first cylinder. Its function is not identical to that of the crankshaft sensor. In one complete revolution of the timing shaft, the crankshaft will turn around the axis twice.
DPKV fixes the TDC of the piston of the first cylinder and gives an impulse to form a discharge for the spark plug. DPRV sends a signal to the ECU, at what moment you need to supply fuel and spark to the first cylinder. Cycles in the remaining cylinders occur alternately depending on the engine design.
The camshaft sensor consists of a magnet and a semiconductor. There is a benchmark (small metal tooth) on the timing shaft in the area of the sensor installation. During rotation, this element passes by the sensor, due to which the magnetic field is closed in it and a pulse is generated that goes to the ECU.
The electronic control unit records the pulse rate. He is guided by them when the fuel mixture is supplied and ignited in the first cylinder. In the case of installing two shafts (one for the intake stroke, and the other for the exhaust), a sensor will be installed on each of them.
What happens if a sensor fails? This video is devoted to this issue:
If the engine is equipped with a variable valve timing system, then the ECU determines from the pulse frequency at what moment it is necessary to delay the opening / closing of the valves. In this case, the engine will be equipped with an additional device - a phase shifter (or hydraulic clutch), which turns the camshaft to change the opening time. If the Hall sensor (or the camshaft) is faulty, the valve timing will not change.
The principle of operation of DPRV in diesel engines differs from the application in gasoline analogues. In this case, it fixes the position of all pistons at top dead center at the moment of compression of the fuel mixture. This makes it possible to more accurately determine the position of the camshaft relative to the crankshaft, which stabilizes the operation of the diesel engine and makes it easier to start.
Additional reference marks have been added to the design of such sensors, the position of which on the master disk corresponds to the inclination of a particular valve in a separate cylinder. The device of such elements may differ depending on the proprietary developments of different manufacturers.
Depending on the type of engine, it may contain one, two or even four gas distribution shafts. To make it easier to determine the type of timing, the following markings are applied to the cylinder head cover:
- SOHC. It will be an in-line or V-shaped engine with two or three valves per cylinder. In it, the camshaft will be one per row. On its rod there are cams that control the intake phase, and slightly offset ones are responsible for the exhaust phase. In the case of engines made in the form of V, there will be two such shafts (one per row of cylinders) or one (placed in the camber between the rows).
- DOHC. This system differs from the previous one by the presence of two camshafts per cylinder bank. In this case, each of them will be responsible for a separate phase: one for the inlet, and the other for the release. There will be two timing shafts on single-row motors, and four on V-shaped ones. This technology allows to reduce the load on the shaft, which increases its resource.
Gas distribution mechanisms also differ in shaft placement:
- Side (or bottom) (OHV or "Pusher" engine). This is an old technology used in carburetor motors. Among the advantages of this type is the ease of lubrication of moving parts (located directly in the engine crankcase). The main disadvantage is the complexity of maintenance and replacement. In this case, the cams press on the rocker pushers, and they transmit the movement to the valve itself. Such modifications of motors are ineffective at high speeds, since they have a large number of control elements for the valve opening moment. Due to the increased inertia, the accuracy of the valve timing suffers.
- Top (OHC). This timing design is used in modern motors. This unit is easier to maintain and repair. One of the drawbacks is the complicated lubrication system. The oil pump must create a stable pressure, therefore it is necessary to closely monitor the oil and filter change intervals (what to focus on when determining the schedule for such work here). This arrangement allows fewer additional parts to be used. In this case, the cams act directly on the valve lifters.
The main reason for the failure of the camshaft is oil starvation. It can arise due to bad filter states or inappropriate oil for this motor (for what parameters the lubricant is selected, read in separate article). If you follow the maintenance intervals, the timing shaft will last as long as the entire engine.
Due to natural wear of parts and an oversight of the motorist, the following malfunctions of the gas distributor shaft may occur.
- Failure of the attached parts - drive gear, belt or timing chain. In this case, the shaft becomes unusable and must be replaced.
- Seizure on bearing journals and wear on cams. Chips and grooves are caused by excessive loads such as incorrect valve adjustment. During rotation, the increased frictional force between the cams and tappets creates additional heating of the assembly, breaking the oil film.
- Oil seal leaking. It occurs as a result of prolonged downtime of the motor. Over time, the rubber seal loses its elasticity.
- Shaft deformation. Due to overheating of the motor, the metal element can bend under heavy load. Such a malfunction is revealed by the appearance of additional vibration in the engine. Usually, such a problem does not last long - due to strong shaking, adjacent parts will quickly fail, and the motor will need to be sent for overhaul.
- Incorrect installation. In itself, this is not a malfunction, but due to non-observance of the norms for tightening the bolts and adjusting the phases, the internal combustion engine will quickly become unusable, and it will need to be "capitalized".
- Poor quality of the material can lead to damage to the shaft itself, therefore, when choosing a new camshaft, it is important to pay attention not only to its price, but also to the reputation of the manufacturer.
How to visually determine cam wear - shown in the video:
Some motorists try to fix some timing shaft malfunctions by sanding damaged areas or installing additional liners. There is no point in such repair work, because when they are performed, it is impossible to achieve the accuracy necessary for the smooth operation of the unit. In the event of a problem with the camshaft, experts recommend immediately replacing it with a new one.
A new camshaft must be selected based on the reason for replacement:
- Replacing a damaged part with a new one. In this case, a similar one is selected instead of the failed model.
- Engine modernization. For sports cars, special camshafts are used in conjunction with a variable valve timing system. Motors for everyday driving are also being upgraded, for example, by increasing power by adjusting the phases by installing non-standard camshafts. If there is no experience in performing such work, then it is better to entrust it to professionals.
What should you focus on when choosing a camshaft that is non-standard for a particular engine? The main parameter is cam camber, maximum valve lift and overlap angle.
For how these indicators affect engine performance, see the following video:
Compared to a complete engine overhaul, the cost of replacing a camshaft is negligible. For example, a new shaft for a domestic car costs around $ 25. For adjusting the valve timing in some workshops will take $ 70. For a major overhaul of the motor, along with spare parts, you will have to pay about $ 250 (and this is in garage service stations).
As you can see, it is better to carry out maintenance on time and not to expose the motor to excessive loads. Then he will serve his master for many years.
Which brands to give preference to
The working resource of the camshaft directly depends on how high-quality material the manufacturer uses when creating this part. Soft metal will wear out more, and overheated metal can burst.
The highest quality and most reliable option is the OEM company. This is a manufacturer of various original equipment, whose products may be sold under different brand names, but the documentation will indicate that the part is OEM.
Among the products of this manufacturer, you can find a part for any car. True, the cost of such a camshaft will be very expensive compared to analogs of specific brands.
If you need to stay on a cheaper camshaft, then a good option are:
- German brand Ruville;
- Czech manufacturer ET Engineteam;
- British brand AE;
- Spanish firm Ajusa.
The disadvantages when choosing a camshaft of the listed manufacturers is that in many cases they do not create parts for a specific model. In this case, you will need to either buy the original, or contact a trusted turner.