Reveal the true face of 'anomalous sound' in the cylinder

The 'anomalous sounds' in the diesel engine and engine cylinder can be summarized into several types: piston knocking sound, piston pin knocking sound, piston bumping sound, piston bumping sound, piston bumping sound, valve knocking sound, cylinder knocking sound, etc. Then Haixing Generator Company will analyze the true faces of these 'anomalous sounds' for everyone.
1. The impact sound of the piston top and the cylinder head
The abnormal sound of the piston top hitting the cylinder head is 'tap' continuous metal hitting sound, which is particularly obvious at high speeds. The abnormal sound source is in the upper part of the cylinder, its sound is solid and powerful, and the cylinder head is vibrating. The main reasons are as follows.
(1) The crankshaft bearing, connecting rod bearing and piston pin holes are seriously worn, and the fitting clearance is seriously exceeded. At the moment when the piston stroke changes, the piston hits the cylinder head under the action of inertia force.
(2) Because other pistons of similar specifications are installed by mistake when replacing the piston, or fake products, the distance between the center line of the piston pin hole to the top surface of the piston is greater than that of the original piston, so that when the piston reaches the upper dead center, it will hit the cylinder head due to its super high.
When driving, if you encounter such a situation, the first aid is to remove the cylinder head and add a cylinder gasket to raise the cylinder head without any collision. However, when repair conditions are available, repairs should be carried out immediately to restore its good technical condition.
2. Abnormal noise at the piston ring.
The abnormal noise at the piston ring is mainly caused by metal hitting the piston ring, air leakage sound of the piston ring, and abnormal noise caused by excessive carbon accumulation.
(1) The sound of metal tapping of the piston ring. After the engine is working for a long time, the cylinder wall is worn, but the upper part of the cylinder wall cannot contact the piston ring almost maintains the original geometry and dimensions, which creates a step for the cylinder wall. If the old cylinder gasket is used or the new cylinder gasket is thin, the piston ring at work will collide with the cylinder wall steps, making a dull 'puff' metal impact sound. If the engine speed increases, the abnormal noise will also increase. In addition, if the piston ring is broken or the gap between the piston ring and the ring groove is too large, it will also cause a larger knocking sound.
(2) The sound of air leakage in the piston ring. The elastic force of the piston ring is weakened, the opening gap is too large or the opening overlaps, and the cylinder wall is pulled with grooves, etc., which will cause the piston ring to leak. Its sound is a 'drink' or 'hiss', and when there is a serious leak, it makes a 'puff' sound. The diagnosis method is to turn off the engine when the engine water temperature reaches above 80℃. At this time, a little fresh and clean engine oil can be injected into the cylinder. After turning the crankshaft for several turns, the engine will be restarted. If the abnormal noise disappears at this time, but it appears again soon, it can be concluded that the piston ring is leaking.
(3) An abnormal sound of excessive carbon accumulation. When there is too much carbon deposit, the abnormal noise from the cylinder is a sharp sound. Because the carbon deposit is burned red, the engine is a bit premature inflamed and it is not easy to shut down. The formation of carbon deposits in the piston ring is mainly due to the lack of tight sealing between the piston ring and the cylinder wall, the gap between the openings is too large, the piston ring is installed and the ring ports overlap, causing lubricating oil to flow upward, high-temperature and high-pressure gas to flow downward, and combustion at the piston ring, resulting in carbon deposits or even sticking to the piston ring, causing the piston ring to lose its elasticity and sealing effect. Generally, after replacing the piston ring with appropriate specifications, this fault can be eliminated.
3. The sound of knocking the cylinder
refers to the abnormal sound of 'dang' or 'dang' or 'dang' caused by the piston swing in the cylinder at the moment the working stroke begins, or when the piston moves upward, and its head and skirt collide with the cylinder wall. If it is a 'dangdang' sound, it is mostly caused by poor lubrication of the cylinder wall. At this time, a little oil can be dripped into the cylinder and then started the engine. If the abnormal noise is reduced or disappeared, it means that the abnormal noise is indeed caused by poor lubrication. If it is a 'click' sound and blue smoke comes out of the exhaust pipe, it is usually due to the large gap between the piston and the cylinder wall. The main reasons for the above situation are as follows:
(1) If this phenomenon occurs only after the cold car starts. When the operation reaches normal water temperature, it disappears on its own because the fitting gap between the piston and the cylinder wall is too large, and the piston shrinks again when the vehicle is cold, which further increases the fitting gap between the two, resulting in a significant knocking sound. After the machine temperature rises, the piston expands and the gap tends to normal, so the abnormal noise disappears. This situation will not have major problems in the short term.
(2) The oil grade does not match the requirements. After the engine is turned off for a long time, when the engine starts again, the oil is viscous and has poor fluidity. In a short period of time, the cylinder wall cannot form a good oil film, and the piston and the cylinder wall directly collide, causing the cylinder to knock. After operating for a period of time, the viscosity of the lubricant oil is normal, and an oil film is formed on the cylinder wall, and abnormal noises weaken or disappear. As long as lubricant is selected reasonably, the engine crankcase is preheated before starting and lubricated with mixed oil, press the starter several times before starting to make the machine parts stick to more lubricant oil. This situation can be avoided.
(3) The mixture entering the cylinder cannot burn normally, resulting in premature combustion or deflagration, or the moment when the engine is loaded with the throttle will be violently pressed, the sound of the domestic plug and the cylinder wall will be generated. The engine should be kept at normal temperature, gasoline that meets the octane requirements should be used, and the ignition time should be adjusted appropriately.
(4) The piston skirt is worn and the cylindrical error is too large. When the piston rises, the top of the piston will hit the cylinder wall, and the piston and the cylinder will be seriously worn, and the gap between the two will be walls. It can be decomposed and inspected, and corresponding repair measures can be taken according to the situation.
(5) Due to the bending and twisting of the connecting rod, the piston pin and the pin hole are deflected, and the two axis core lines of the crank pin and the piston pin are not parallel, etc., it will also cause the piston to deflect in the cylinder and impact the cylinder wall. This situation can only be decomposed and inspected, and then replaced with the corresponding parts after diagnosis.
4. The sound of the piston pin hitting
the piston pin hole, the piston pin and the connecting rod small head bushing (or bearing) is too large, and a sharp, crisp and highly tone metal hitting sound will be made, similar to the sound of hitting the iron drill with a small hand hammer. The rule is that the engine does not sound when the engine starts, and the temperature rises, the louder it sounds, and the higher the temperature. If the ignition time is pre-adjusted, the sound will be accelerated and increased. If the spark plug is cut off, the sound will weaken or disappear.
Some engines not only have a large gap between the piston pin and the pin hole, but also have a large gap between the piston pin and the connecting rod small head bushing (or bearing). In this case, the knocking sound is relatively complicated and there will be continuous 'click' sound.
In addition to the wear during work, the gap between the piston pin, piston pin hole and connecting rod small head bushing are steel, aluminum and copper respectively. The expansion coefficients vary greatly. If you are a little careless, the gap between the three will become larger due to heat expansion, causing mutual impact. Moreover, when the gap increases, the axial momentum of the piston pin also increases, and the cylindrical end surface of the pin will impact the pin ring, which adds an abnormal noise in the cylinder.
5. Abnormal noise of the valve
(1) The abnormal noise of the exhaust valve leak can be heard at the exhaust pipe muffler, such as the 'sighing' sound when the tire is seriously leaking. The valve leakage can be heard at the air filter at the upper end of the carburetor, and its sound is like the 'sheep' sound when a child whistles. The reason is that the working surfaces of the valves and races are severely worn or ablated, with grooves and spots that cannot be tightly sealed. Some are caused by the gap between the valve stem and the conduit too large or the valve stem is bent, which makes the valve head unable to be centered and tilted, causing air leakage. If the valve spring force is weakened or broken, the valve cannot fit closely with the seat race working surface, which will also cause air leakage. From the assembly point of view, if the gap between the valve stem and the conduit is too small, it is stuck due to heat expansion during work, or the valve gap is adjusted too small, the valve stem is extended by the lifter or rocker arm and is pushed open to the valve, which will cause the valve to be unable to be completely closed and leak.
(2) The abnormal sound when the valve spring breaks varies depending on the valve placement method. After the side valve spring breaks, it makes a 'crack' sound when working. If the valve cover is removed, it will be heard more clearly. After the overhead valve spring breaks, the valve automatically sinks, which will impact the piston and a 'dangdang' knock sound will appear. If the latter fails to shut down in time, it will cause the piston to be broken, the connecting rod will be broken, and even more serious losses.
(3) Too much carbon deposits in the valve can also cause abnormal noises, because too much carbon deposits, the carbon layer is hot, the piston temperature is high, the gap between the piston ring groove and piston pin hole increases, thus making a 'chat' abnormal noise. This fault is often accompanied by excessive temperature, difficult engine shutdown or failure to shut down. The reason is that the proportion of engine oil in the mixed oil exceeds the standard or the oil pan oil penetrates into the combustion chamber in large quantities. The specific reasons should be further identified and eliminated.
6.
When the engine load increases, some engines make 'click' sounds from the cylinder, which is different from the sounds during normal operation, and even the phenomenon of deterioration in acceleration performance. This abnormal sound is louder and can be heard 5-6m away from the engine. The abnormal sound is particularly obvious when the sudden acceleration is accelerated, so it can be regarded as a sign of engine knock. When the combustible mixture is burning too fast in the cylinder, it instantly releases a large amount of heat, causing the pressure in the cylinder to rise sharply, and the high-pressure gas strongly impacts the piston top, cylinder head and cylinder wall, causing a knock. The main reasons for knocking are that the engine is overheating, the ignition time is too early, the carbon deposit in the combustion chamber, the octane value of the gasoline is too low, the heat value of the spark plug used is too low, and it does not meet the requirements.