We go to the repair shop to fix the car, and often we see some engines overhauled. Ask the repairman the reason for the overhaul of these engines, which is nothing more than "pulling the cylinder", "turning the tile", "bursting the cylinder", "top cylinder", "seriously burning oil" and so on. For those of us who are repairing cars, these words are tantamount to the "black words" of Yang Zirong asked by the mountain eagle. Today Lao Hou used as blunt a language as possible to tell you what these words mean, to see where the "pulling cylinder" is pulling? What does the "burst cylinder" explode? How is the "top cylinder" top? How can we avoid these failures in our daily use.
To illustrate this problem, we must first briefly introduce a little knowledge about automobile engines. The engine used on the car, the full name is "four-stroke water-cooled reciprocating piston engine", the piston in the cylinder up and down reciprocating movement, complete the intake, compression, work, exhaust four strokes, and through the connecting rod to transmit the power to the crankshaft, drive the crankshaft rotation, the power output outward. In this process, a pair of "joyful enemies" play a crucial role: piston-cylinder. They are also the largest moving friction pair in the engine and are the most core mechanism of the engine.
First, let's talk about pistons. The piston is a cylinder that moves up and down in the engine cylinder, which is combined with the cylinder head and the cylinder wall to form a combustion chamber, in which the fuel is burned, and the generated high temperature and high pressure gas pushes the piston downward movement, and transmits this thrust to the crankshaft through the connecting rod, driving the crankshaft to rotate and do work. The working environment of the piston is extremely harsh, and its top is in direct contact with high-temperature, high-pressure, corrosive gases, withstanding the action of huge gas pressure and inertial forces, and constantly friction occurs between the piston surface and the cylinder wall during high-speed movement. Therefore, the piston must have sufficient strength and stiffness, and have wear resistance, high temperature resistance, the smaller the quality, the better.
Pistons are usually cast from silicon aluminum alloys, and some highly reinforced diesel engines are made of high-grade cast iron or heat-resistant steel. The piston is structurally divided into three parts: top, head and skirt. The top and the cylinder head, cylinder wall constitute a combustion chamber, its shape determines the shape of the combustion chamber, is an important factor affecting the state of fuel combustion; the head is used to install the piston ring, the main role is to seal the cylinder, and the heat of the piston is transferred to the cylinder wall; the skirt is mainly to the piston motion guidance, and to withstand the cylinder wall to apply the side pressure of the piston, the current household gasoline engine usually uses a drag plate piston skirt. The piston is in the shape of a small and large cone, and the upper part is more heated and expands more when working, becoming almost circular.
The piston is deformed by thermal expansion when working, but its deformation is not uniform. The top of the piston will be bent and deformed under the action of gas pressure, deformed along the axis of the piston pin under the action of side pressure, there will be more metal at the bore of the piston pin seat, the heating will be oval deformation, the upper part will be heated more deformation, and the lower part will be less heated and less deformed. Oval deformation of the piston can break the fit with the cylinder wall and cause the engine to work abnormally. Therefore, the piston will also do some thermal insulation and compensation measures in the structure, such as opening the insulation groove, expansion groove, using an oval tapered skirt, and inlaid with a constant van steel sheet in the piston.
In addition, it is also very important to strengthen the cooling and lubrication of the piston, some high-strength engines have special oil nozzles, cool the piston injection oil, use oil rings to spread oil on the cylinder wall to form oil film lubrication pistons, the piston surface is phosphating treatment, or apply graphite, spray PTFE coating, etc., to improve the wear resistance and high temperature resistance of the piston.
Let's talk about the engine cylinders. A cylinder is a cylindrical cavity in an engine that guides the piston up and down. It is also an integral part of the combustion chamber, to withstand huge gas pressure and high temperature, corrosion, etc., so it is required to have sufficient strength and heat resistance, wear resistance. In order to save materials, reduce costs, and ensure engine service life, in the vast majority of engines, the cylinder liner will be inserted into the cylinder to form a cylinder working surface.
Cylinder liners are made of alloy cast iron or alloy steel with good heat resistance, and the cylinder block is cast with cheaper ordinary cast iron or aluminum alloy, and when the cylinder liner is excessively worn, it can also be repaired or replaced separately, which can reduce the cost of use and maintenance. Some aluminium engines do not have a cylinder liner, but instead electrochemically process a hard alloy coating on the cylinder wall. In addition, the inner wall of the cylinder liner is machined into a grid, which can form a tiny oil storage tank to enhance the lubrication of the piston.
The cylinder liner is fixed and immovable, and the piston moves up and down in the cylinder liner, forming a moving friction pair. An ordinary household gasoline engine, assuming a piston stroke of 87mm, when the engine is running at 2000 rpm, the relative speed of the two is nearly 6 m/ s. Such a high friction speed, if there is no good lubrication and heat dissipation, the friction pair will soon be destroyed, so the piston-cylinder lubrication and heat dissipation is the core technology of the engine. In addition, due to the presence of side pressure and gas pressure, the piston does not run in the middle position of the cylinder, but is biased to one side when going up and down, and the wear in the direction of side pressure is more serious, so a bias grinding is formed, which is an inevitable defect of reciprocating engines.
There is a gap of about 0.05 to 0.1 mm between the piston and the cylinder liner, which is called the "cylinder clearance". Different engines have slightly different values, the general cast iron cylinder block matching aluminum alloy piston will be slightly larger, and the aluminum alloy cylinder block will be slightly smaller with aluminum alloy piston. Such a small mating gap requires a sophisticated machining process and equipment to achieve. We usually say that the engine is made precisely, mainly referring to this part. In addition, the thermal expansion of the metal is also a factor that must be considered, using different metal materials, different coefficients of thermal expansion, and different cylinder clearances. These are the most core technologies of the engine.
It should be noted that this parameter is the data during cold rolling, and the gap between the piston skirt and the cylinder wall is measured. When the engine reaches the normal operating temperature, this gap will be reduced to about 0.02 ~ 0.05mm. If this gap is too large due to wear, the sealing performance of the piston-cylinder will be greatly reduced, the cylinder pressure will be reduced, the combustible mixture entering the combustion chamber will be compressed insufficiently, it is difficult to burn, and it will leak out from the gap between the piston-cylinder wall, forming the so-called "lower exhaust", the engine power will decrease, and the oil consumption will increase sharply, in this case, the engine will need to be overhauled.
Knowing the characteristics of the piston and cylinder and the motion relationship between the two, it is possible to explain the terms such as pulling cylinder and burst cylinder.
As mentioned earlier, the gap between the piston and the cylinder is very small. If there is hard particles entering this gap, under the action of the high-speed movement of the piston and the huge inertia, it will cause scratches to the cylinder wall and the piston surface, forming a longitudinal groove on the surface of the cylinder wall, which is the so-called "pull cylinder". Therefore, in simple terms, the "pull cylinder" is a longitudinal scratch on the inner surface of the cylinder wall. The reason for the pulling cylinder is generally that there are impurities entering the combustion chamber, such as carbon particles that fall off, hard particles in the air, etc., in addition to the piston ring is broken, the piston pin spring falls, the piston pin is channeled out, etc., which will also cause the cylinder to fail.
When the engine has a pull cylinder failure, due to leakage at the scratch, the sealing of the cylinder decreases, the engine will appear abnormal, jittery and other phenomena, the engine power will decline, the lower exhaust will increase, and a wisp of smoke will be seen at the oil gauge from here. If it is a slight pull cylinder, the engine can continue to be used, but to avoid heavy load operation. If it is a serious pull cylinder, it must be stopped for repair. An important measure to avoid pull-out failure is to use a good quality air filter and maintain a good seal in the intake line, which can completely filter the hard particulate matter in the air and avoid getting stuck in the cylinder into the piston-cylinder friction pair. In addition, reducing carbon deposits in the combustion chamber of the engine is also one of the measures to avoid pulling cylinders.
So what is the "burst cylinder"? Everybody listen, burst the cylinder, wow, the engine exploded yay!
Not really. Today's car engines are very safe and will never explode. The so-called "burst cylinder" actually refers to the failure of the piston and cylinder liner stuck.
As mentioned earlier, when the engine is working normally, the gap between the piston and the cylinder wall is very small. But this is based on the fact that the engine dissipates heat well. If the engine heat dissipation is not good, or long-term heavy load work, then the temperature of the piston will rise sharply, a large expansion deformation occurs, and the cylinder block expansion is not as large as the piston, so the gap between the piston and the cylinder liner will disappear, and the two will change from clearance to interference. Under the action of the inertial force of the flywheel, the piston still maintains a reciprocating motion up and down, and serious friction occurs between the cylinder wall, generating a large amount of heat, so that the piston shows that it melts with the metal on the inner surface of the cylinder wall, and welds together, and then tears. At this time, the surface of the piston and the cylinder liner is completely damaged, the friction pair is completely destroyed, resulting in huge resistance forcing the engine to stop running, and the high temperature makes the piston and the cylinder liner fused together, and the engine cannot work at all.
Burst cylinders are generally caused by high engine temperatures. At this point, the coolant in the engine will boil, and the smoke in the engine compartment will be swirling, as if it exploded, so it is called "burst cylinder". Burst cylinder is a serious mechanical failure, the piston and cylinder liner in the engine are stuck, completely incapacitated, and must be disassembled and repaired. If the car explodes at high speed, it will even cause the car to lose control, which is one of the very dangerous engine failures. Therefore, in our daily use, we must maintain a good heat dissipation ability of the engine, if the engine temperature is too high, we must stop and check, and we must not run with disease.
Let's talk about how the engine "top cylinder" is topped. There are two cases of engine top cylinders, one is the piston top collides with the valve top, and the other is the piston top water or other foreign objects.
When the engine is in operation, the piston reciprocates up and down. When the piston reaches the upper stop point, either the exhaust is finished, or the compression is final. If it is the final position of the exhaust, the intake and exhaust valves are open at this time, and the valves are stacked. The gap between the valve and the piston top at this time is less than one millimeter. In addition, while the piston moves up and down, the valve also opens or closes, maintaining a specific motion relationship and ensuring that the two do not interfere with the movement.
This specific kinematic relationship is done by the engine gas distribution mechanism. If the distribution mechanism fails, such as timing belt breakage, timing chain jumping teeth, camshaft breakage, etc., the valve no longer moves with the piston, but remains in a certain position, and the motion relationship between the valve and the piston will be broken. When the piston moves to the upper stop point, the top of the piston moving at high speed collides with the open valve, breaking or cracking the piston, breaking or bending the valve, and even breaking the cylinder head and cylinder block in severe cases, and the engine is completely damaged. If the car is in the high-speed driving of the top cylinder accident, the car will lose power in an instant, the engine is damaged or stuck, and the car is very easy to lose control.
The vast majority of this top valve type top cylinder is caused by the timing belt or timing chain not replaced in time. Therefore, we must replace the timing belt or timing chain on time according to the requirements of the maintenance manual. Don't listen to the lies of some old drivers: if you look good, you don't have to change. The consequences caused by the top cylinder are extremely serious, the engine is basically completely scrapped, and it only takes a few hundred dollars to change a belt.
Another type of top cylinder is when the piston is pushed against water or other foreign objects.
When the engine is working, in the compression stroke, the top of the piston compresses the combustible mixture. The gas is more compressible and can be compressed into a very small clump. But if the engine wads through water and it is water instead of air that is sucked into the cylinder during the intake stroke, then what the piston compresses in the compression stroke is water, and water is incompressible. If we force the car to start, the piston is forced upwards under the impetus of the starter, and when it encounters water enclosed in the cylinder, it will be blocked by the water and unable to go up. At this time, the starter continues to rotate the crankshaft, the connecting rod continues to push the piston upwards, under the action of huge resistance, the connecting rod will be bent and deformed, and the valve will also be bent due to the impact of the water, which is the so-called engine wading top cylinder. If you replace the water with other incompressible foreign objects, such as screws, spark plugs on the head, etc., the consequences are the same. Therefore, the engine must not be started twice after wading through water and turning off.
The above-mentioned engine top cylinder, if the consequences are very serious, will cause the piston linkage to break. The connecting rod swings freely at high speed in the engine, which breaks the cylinder block, which causes another serious failure: the cylinder. After the cylinder is pounded, the engine shell is completely ruptured, and the internal parts will basically be deformed and damaged, and the engine will be completely scrapped.
Finally, to sum up: engine pull cylinder refers to the piston and the cylinder liner between the impurities, in the cylinder line formed a longitudinal groove, this situation only needs to replace the damaged piston and cylinder alone; burst cylinder is the engine high temperature caused by the piston and cylinder locking, in this case need to replace the engine "four matching", that is, piston, piston ring, piston pin, cylinder liner, not through the explosion cylinder is generally accompanied by the thermal deformation of the cylinder block and cylinder head, the later stage is easy to occur oil leakage, water leakage, cylinder gas gas pad and other failures The very serious mechanical accident of the top cylinder, the engine of the top cylinder has basically no maintenance value, and it is generally necessary to replace the engine assembly, or replace the middle cylinder.