- Apr 16, 2018 -
Knowledge of chainsaw!Why does the chainsaw scratch the cylinder?
The cause of the engine cylinder has a lot of, for the average user even many technical personnel engaged in related work, to quickly and accurately analysis, determine the cause of the malfunction, and is not an easy thing.Today, I analyzed the main reasons of the cylinder, hoping to help users and maintenance personnel.
When the engine is working, the piston and piston ring are reciprocating in the cylinder.With the large expansion thrust produced by the mixture combustion, the piston and piston ring are closely connected with the inner wall of the cylinder through the oil film formed by the oil.Under normal circumstances, as a result of the oil film isolation and cushioning, piston and piston ring is not direct contact with cylinder, however, in certain cases, both will directly contact, sliding friction, and generate a lot of heat, if not effectively improve heat dissipation condition, could melt the piston, piston ring and cylinder wall surface, make the sliding friction surface fuses in together, the longitudinal tensile mark in the high speed movement of the piston, serious when both lock, namely so-called cylinder occur.
The main reasons are as follows:
1. The engine is running low in the initial stage, and the cylinder is caused by high-speed operation.
For new engine just assembly, seemingly smooth the inner surface of cylinder and piston, piston ring of peripheral surface, is actually made up of countless micron grade of rugged ridges, before the engine can follow one's inclinationsly real operation, have to cooperate with surface in the early, bulging cut to the peak, the surface is smooth, uniform stress, while sliding, interlocking, running to chang.Therefore, the new engine must undergo some degree of running-in after assembly.Otherwise, on the piston, piston ring and cylinder with high ridges, will be under concentrated load, the pressure per unit area is very large, and after the friction temperature rise, softening, melting, so that cylinder.
2. Cylinder caused by overheating of piston.
Local abnormal expansion occurs when the piston overheats.Due to the deformation of the piston, the piston ring groove is twisted into a wave shape, and the piston ring and ring groove are short or even long, causing the piston ring to be unable to work properly.At this time, an edge of piston ring with extremely high pressure per unit area of the direct contact with the inner wall of the cylinder friction, make the function of piston ring not only lost the combustion gas sealing, and destroyed the cylinder oil oil film on the wall, leading to a cylinder.
The main causes of piston overheating are:
The poor quality of gasoline produces high temperature caused by abnormal combustion of mixture.
The oil supply system, ignition setting or adjustment is bad, resulting in the abnormal combustion of the mixture and the high temperature;
The piston body design is bad or the density difference of the piston aluminum parts makes the piston overheat due to the insufficient heat transfer from the piston to the cylinder.
The external cooling of the engine is not sufficient to cause overheating.
3. Cylinder caused by improper travel of piston.
When the engine is running, the combustion chamber inevitably produces carbon.Although the oil and piston rings have the function of removing carbon, it is very difficult to remove the carbon deposition in the piston ring groove, especially in the first gas ring groove.When the carbon deposition inside the ring grooves increase gradually, will bring piston ring the improper clearance and back lash, hinder the activities of the piston ring, abnormal pressure to the piston ring, piston ring and cylinder wall direct contact friction, causing cylinder.
There are several reasons for carbon deposition in combustion chamber:
The use of gasoline is poor quality;
Abnormal combustion of mixed gas;
The mixture of the oil supply system is too strong;
The ignition system, especially spark plug ignition failure;
Excessive oil residue on the inner wall of the cylinder;
The oil is leaking from the cylinder cover to the combustion chamber.
4. Cylinder with improper clearance between piston and cylinder.
Due to the poor machining accuracy of cylinder inner diameter and piston and piston ring outside diameter, the gap between piston and cylinder is improper.During the interval, the piston and cylinder contact pressure increase or even die.Clearance is too large, the piston head throwing more, piston skirt and cylinder head part of the contact, or piston ring and cylinder part of an edge contact, pressure per unit area is very high, leading to a cylinder.
5. Cylinder with poor surface shape of piston and cylinder.
When the engine is working, the ideal shape of the contact surfaces of the pistons and cylinders should be cylindrical, so that they can be evenly distributed throughout the two places to avoid the pressure of the large surface.Due to the effect of thermal expansion and contraction, the shape of the piston skirt is in the shape of a barrel on the vertical and an elliptical shape on the horizontal.This complex geometry has high precision requirements.However, due to the design, manufacturing process or material reasons, it may cause the shape not ideal and cause the cylinder.
The main reasons are:
The machining accuracy of piston skirt is not enough to cause shape distortion.
The surface shape of the cylinder is poor (roundness and cylindric).
(3) piston pin diameter or piston pin hole diameter machining accuracy is insufficient, lead to the gap between the two is too small, or a foreign body between the two, so that when the engine running and expanding and piston pin, pin hole, holding in death of the obstruction of piston skirt in the expansion of the pin hole direction, causing the skirt can't achieve ideal shape;
(4) piston skirt structure design bad lead to insufficient rigidity, bearing surface compression deformation before and after the skirt sag, makes the skirt side 45 ° direction on local stress increases with the cylinder;
When the cylinder liner is poorly designed or the material is defective, the cylinder is deformed, so that the piston and the cylinder are close to the upper stop and the friction increases, causing the cylinder to be drawn.
6. The surface treatment caused by poor drawing cylinder.
From the material point of view, piston, piston ring, high-speed motion within the cylinder, friction heat production, serious when they make the metal surface melting and bonding together, therefore, generally speaking, the piston, piston ring and cylinder inner surface of a variety of surface treatment, such as chrome plating, nickel plating, spraying molybdenum, nitride, phosphide and PVD (physical vapor deposition), etc., make its surface covered with a high melting point materials, so as to achieve the aim of not easy to produce high temperature fusion.However, if the surface treatment is not good, such as the coating thickness is insufficient, the adhesion difference, the piston and the ring and the cylinder occur high temperature fusion, it is inevitable.
7. Pull cylinder caused by oil lubrication failure.
When the engine is working, the oil is formed between the cylinder and the piston and piston ring to form an oil film, which can effectively avoid the direct contact friction between the two.However, the following situations can make the engine oil fail to give full play to its lubrication effect, thus causing the cylinder:
There is not enough oil.It is obvious that when the engine oil quantity is insufficient, the engine oil is constantly consumed in the running process and cannot be replenished in time, and the oil film with sufficient thickness cannot be established.
Oil emulsification.Especially in winter, when the engine temperature is reduced, cylinder barrel bottom and inside the crankcase (from vent inhalation moisture in the air condenses into water mixed with oil, will gradually lead to the oil emulsion.At the same time, the mixture of leakage from the combustion chamber is also continuously integrated into the oil to promote the emulsification of oil.After emulsification, the oil concentration becomes thin and the oil can deteriorate. It is not easy to establish an effective oil film between the cylinder and piston and piston ring.
The choice of oil brand is not correct.Depending on the region and season, the oil should be selected according to the appropriate number of oil. If the choice is not correct, the oil will be too sticky in winter, the liquidity is poor, or the oil will be too thin in summer, which will lead to poor lubrication.
8, foreign body, impurity caused by the cylinder.
When there is a hard foreign body between the cylinder and piston and piston ring, the foreign body plays the role of the research material, causing the surface of the two to accelerate the wear, and the cylinder is serious.
Foreign sources mainly have the following aspects:
The cleaning of the engine parts is not clean and brought into the dust and other foreign matter;
A residual burr on the engine part;
The grinding of iron filings and aluminum scraps during the operation of the engine;
The dust is filtered by the air filter.
The carbon deposition produced by the incomplete combustion of oil and mixed gas;
The iron sand left in the muffler is poured into the combustion chamber.