The abnormal noises in the cylinder of the diesel generator set engine can be summarized as the sound of piston knocking, piston pin knocking, piston top hitting against the cylinder head, a shock from the top of the piston, a knock of a piston ring, a knock of a valve. several types of knocking and cylinder knocking noises.
1. The impact sound of the top of the piston and the cylinder head
The abnormal sound of the top of the piston hitting the cylinder head is a continuous metallic knocking sound. "tat-tat-tat" sound There is a clicking sound, especially at high speed. The source of the abnormal noise is in the upper part of the cylinder, the sound is solid and loud, and the cylinder head vibrates. The main reasons are as follows.
(1) The crankshaft bearing, connecting rod bearing and piston pin hole are severely worn and the corresponding clearance greatly exceeds the standard. At the moment when the stroke of the piston changel, the top of the piston hits the. cylinder head under the action of the force of inertia.
(2) Due to the incorrect installation of other pistons with similar specifications when replacing the piston, or counterfeit and substandard products, the distance between the center line of the hole of the piston The piston pin and the upper surface of the piston is larger than the original piston, causing the piston to reach top dead center. Cylinder head collision due to excessive height.
If you encounter such a situation while driving, the first aid method is to remove the cylinder head and add a cylinder gasket to lift the cylinder head to avoid collision again. However, when repair conditions exist, repairs must be carried out immediately to restore its good technical condition.
2. Abnormal noise at the piston ring area
Abnormal noise at the levelau of the piston ring area mainly includes the metal knocking noise of the piston ring and air. Leaking piston ring. Abnormal noise and noise caused by excessive carbon deposits.
(1) Metallic knocking noise from the piston rings. After prolonged operation of the engine, the cylinder wall is worn, but the upper part of the cylinder wall that is not in contact with the piston ring almost retains its original geometric shape and size, which creates a step on the cylinder. wall. If an old cylinder seal is used or a new one is too thin, the working piston ring will collide with the cylinder wall step, producing a dull metallic impact noise. 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 causet a loud knocking noise.
(2) The sound of air leaking from the piston rings. The elasticity of the piston ring is weakened, the opening space is too large or the openings overlap, and the cylinder wall has grooves, etc., which will cause the piston ring to leak. The sound is a "drinking" or "hissing" sound, and when there is a large air leak, it will make a "hissing" sound. The diagnostic method is to stall the engine when the water temperature exceeds 80°C. At this time, you can inject some fresh, clean engine oil into the cylinder. After cranking the crankshaft for a few revolutions, restart the engine. this time, if the abnormal noise disappears, it will start again soon. If it appears, it can be concluded that the piston ring is leaking.
(3) Abnormal sounds due to excessive carbon deposits. When there is too much carbon deposit, the abnormal noise coming from the cylinder is ahigh pitched sound. Because the carbon deposit is burned red, the engine exhibits symptoms of premature ignition and is difficult to stall. The formation of carbon deposits on the piston ring is mainly due to lax sealing between the piston ring and the cylinder wall, excessive opening clearance, reverse installation of the piston ring, overlapping of the ring openings , etc., resulting in channeling of lubricating oil. , high temperature and high temperature.The compressed gas flows downward and burns at the piston ring, causing carbon deposits and even sticking to the piston ring, making the piston ring lose its elasticity and d waterproofing. Generally, this fault can be eliminated after replacing the piston ring with a suitable specification.
3. Cylinder knocking noise
Cylinder knocking refers to when the piston startsits working stroke, or when the piston rises, the piston is in the cylinder The resulting swing causes the head and skirt to collide with the cylinder wall, causing an abnormal "popping" or "clicking" sound ". If there is a “dang-dang” noise, it is mainly due to poor cylinder wall lubrication. At this time you can pour some oil into the cylinder and restart the engine. If the abnormal noise is reduced or disappears. this means that the abnormal noise is indeed caused by poor lubrication. If there is a "click" and blue smoke is emitted from the exhaust, this is usually due to too large a gap between the piston and the cylinder wall. The main reasons for the above situation are:
(1) If this phenomenon only occurs after the car is started from cold. It will disappear automatically when the water temperature reaches normal operation.This is because the fit gap between the piston and the cylinder wall is too large. When the car is cold, the piston shrinks, further increasing the adaptation gap between the two. with an obvious knocking noise. Once the machine temperature rises, the piston expands and the deviation tends to the normal value, so the abnormal noise disappears. This situation will not pose any major problems in the short term.
(2) The quality of the engine oil does not meet the requirements. When the engine restarts after a long period of stalling, the engine oil is viscous and not very fluid. A good oil film cannot form. the cylinder wall in a short time, and the piston and the cylinder wall are directly connected. The collision causes the cylinder to knock. After a period of operation, the viscosity of the lubricating oil will be normal, an oil film will form on the cylinder wall, and the noise will be abnormal.l will weaken or disappear. As long as the lubricating oil is correctly selected, the engine crankcase is preheated before starting and lubricated with mixed oil, then press the starting lever several times before starting to allow more lubricating oil to adhere to the machine parts. Avoidable.
(3) The mixture entering the cylinder cannot burn normally, resulting in pre-ignition or deflagration, or when the accelerator is slammed when the engine is not loaded , the sound of the piston hitting the cylinder a wall will be realized. The engine should operate at normal temperature, use gasoline that meets octane requirements, and adjust the ignition timing accordingly.
(4) The piston skirt is worn and the cylindricity error is too great. As the piston moves upward, its top hits the cylinder wall. The piston and cylinder are seriouslyworn and the wall of the space between them. they are. It can be inspected after disassembly and corresponding repair measures can be taken depending on the situation.
(5) Due to the bending and twisting of the connecting rod, the deviation of the piston pin and the pin hole, the non-parallel axes of the crankpin and the pin piston, etc., it the piston will also be deflected in the cylinder and hit the cylinder wall. In this case, it can only be inspected after disassembly, and the corresponding parts can be replaced after diagnosis.
4. The knocking noise of the piston pin
Piston pin and piston pin hole, piston pin and big end bushing (or bearing) If the gap is too large, a sharp, sharp, sharp metal knocking sound will be emitted, similar to the sound of a small hand hammer hitting an iron drill. The rule is to initiateThere is no sound when the engine is cold and the car starts.fed up, but it will sound when the temperature rises, and the higher the temperature, the louder the sound will be. If the ignition time is advanced, the sound will speed up and become louder. If the spark plug is cut, the sound will weaken or disappear.
Some engines not only have a large gap between the piston pin and the pin hole, but also a large gap between the piston pin and the big end bushing (or bearing) . the knocking noise is more complicated and may produce a continuous “tacking” sound.
The reason for this failure is that in addition to wear during work that widens the gap, the piston pin, piston pin hole and foot ring connecting rod are made of steel, aluminum and copper during assembly. Their expansion coefficients are very different. If you are a little careless, the gap between the three will become larger due to different thermal expansion during work, prevoking collisions with each other. In addition, when the gap increases, the axial movement of the piston pin also increases, and the cylindrical end surface of the pin hits the pin ring, adding abnormal sound in the cylinder.
5. Abnormal valve noise
(1) Abnormal sound of exhaust valve leakage can be heard from the exhaust pipe muffler, such as "squealing". " sounds when a tire is severely deflated. A valve leak can be heard at the air filter on the top of the carburetor, and the sound resembles the “shh” of a child whistling. The reason is that the working surfaces of the valve and seat are heavily worn or ablated, grooves and stains appear and cannot be tightly sealed. In some cases, the gap between the valve stem and the conduit is too large or. the valve stem is bent, preventing thevalve head from being centered and tilted, causing an air leak. If the elastic force of the valve spring is weakened or broken, the valve will not be able to fit closely with the working surface of the seat ring, 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 will expand due to heat during operation and get stuck, or if the valve clearance is set too small , the valve stem will be stretched due to heat and the valve will be pushed open by the lifter or rocker arm, which will prevent the valve from closing completely and cause air leakage.
(2) The abnormal noise when the valve spring breaks varies depending on the valve placement method. Once the valve spring is mounted on the broken side, it will make a "click" sound during operation. You can hear it more clearly if you remove the coverof valve. After the overhead valve spring breaks, the valve automatically depresses, collides with the piston, and makes a “dang-dang” knocking noise. If it is not extinguished in time, it will cause piston rupture, connecting rod rupture, and even more serious losses.
(3) Too much carbon deposit on the valve will also cause abnormal noise. Because there is too much carbon deposit, the carbon layer will be hot, the piston temperature will be high, and the gap between the two. The piston ring groove and piston pin hole will increase, producing a "chatter" sound. This fault is often accompanied by phenomena such as an engine temperature that is too high and an engine that is difficult or even incapable of stalling. The reason is that the proportion of engine oil in the mixed oil exceeds the standard or a large amount of oil from the oil pan leaks into the combustion chamber. The specific causeic needs to be further identified and eliminated.
6. Abnormal noises from the combustion chamber
When the engine load increases, some engines will emit a “click” from the cylinder, which is related The sound during normal operation is different and the Acceleration performance is even worse. This type of abnormal noise is loud and can be heard at a distance of 5-6m from the engine. You may hear an abnormal noise, especially obvious during sudden acceleration, which can be considered a sign of engine knocking. When the combustible mixture burns too quickly in the cylinder, it instantly releases a large amount of heat, causing a sharp increase in pressure in the cylinder. The high pressure gas strongly impacts the top of the piston, cylinder head and cylinder wall, causing knocking. The main reasons for knocking include engine overheating,premature ignition time, excessive carbon deposits in the combustion chamber, low octane number of gasoline, low calorific value of the spark plug used, etc.