Piston Anodizing

With the continuous increase of diesel engine output power, the thermal and mechanical stresses borne by the piston also increase accordingly, leading to cracking and erosion of the combustion chamber wall around the piston top. Due to the hard oxide film, the heat resistance of the aluminum piston top surface can be effectively improved, which has an extremely good inhibitory effect on thermal cracking, especially on the tendency of thermal cracking at the combustion chamber edge of direct injection diesel engines. Therefore, high-power pistons generally need to undergo anodizing treatment.
judgment
During the operation of the vehicle, there is a piston knocking noise in some parts of the engine. The location of the abnormal noise caused by the piston knocking on the cylinder is at the upper part of the cylinder, which is a rhythmic "click" sound similar to hitting a cement floor with a small hammer. When the engine is idling, the sound is obvious and clear. Especially when the engine is running at low temperatures, the sound is obvious, and after the temperature rises, the sound decreases or even disappears.
The judgment method for piston knocking cylinder:
(1) Cut off the oil cylinder by cylinder. The method of cutting off oil cylinder by cylinder is adopted to determine the position of knocking cylinder. If the sound decreases or disappears significantly when the oil is cut off to a certain cylinder, and a clear "clacking" sound can be heard when the oil supply is restored, it indicates that the piston of that cylinder is knocking cylinder.
(2) To further confirm the knocking of the cylinder piston, the fuel injector of the cylinder can be removed, and a small amount of CD grade turbocharged oil (for sealing) can be added to the cylinder. Then, the fuel injector can be installed, and the engine can be started. If the knocking sound disappears or weakens and reappears after running for a while, it is undoubtedly the knocking of the cylinder piston.
The main reasons for piston knocking are as follows:
(1) The gap between the piston and the cylinder wall is too large. The standard clearance between the piston skirt and cylinder of the WD615 series engine is 0.143-0.182, with a maximum wear limit of 0.35-0.40.
(2) After running the engine for a period of time, the cylinder piston wears out, coupled with poor lubrication, the clearance between the piston and cylinder increases due to wear, and a serious step appears slightly below the first air ring, causing the piston to strike the cylinder and make abnormal noises.
(3) After running for a period of time, the piston skirt and cylinder wear severely, causing severe roundness loss and knocking of the cylinder.
(4) Due to various reasons, some connecting rods have deformed, causing the piston to wear unevenly and the clearance to increase, resulting in knocking of the cylinder. Piston knocking can lead to excessive fuel consumption, engine oil leakage, high oil consumption, and poor fuel efficiency in the engine. When the piston hits the cylinder severely, it can also break the piston, damage the cylinder, and cause the connecting rod to break, damaging the cylinder body.