Judgment method for piston knocking:

(1) Cut off oil cylinder by cylinder. The method of cutting off oil cylinder by cylinder is adopted to determine the position of knocking the cylinder. If the oil is cut off to a certain cylinder, the sound significantly decreases or disappears, and when the oil supply is restored, a clear "click" sound can be heard, indicating that the piston of the cylinder is knocking the cylinder.

(2) To further confirm that the piston of the cylinder is knocking, the fuel injector of the cylinder can be removed, a small amount of CD grade turbocharged oil can be added to the cylinder (for sealing purposes), and then the fuel injector can be installed to start the engine. The knocking sound disappears or weakens, and after running for a while, the knocking sound reappears, indicating that the piston of the cylinder is knocking.

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 WD615 series engines is 0.143-0.182, and the maximum wear limit is 0.35-0.40.

(2) After the engine has been running for a period of time, the cylinder piston experiences wear, coupled with poor lubrication. The fit gap between the piston and the cylinder increases due to wear, and a severe step appears slightly below the first air ring, causing the piston to strike the cylinder and make a strange noise.

(3) After running for a period of time, the piston skirt and cylinder are severely worn, resulting in severe loss of roundness and knocking of the cylinder.

(4) Individual connecting rods deform due to various reasons, resulting in eccentric wear of the piston, increased clearance, and knocking of the cylinder. Piston knocking can cause excessive fuel consumption, engine oil leakage, high oil consumption, and poor economy in the engine. When the piston knocks the cylinder severely, it will also break the piston and damage the cylinder, causing the connecting rod to break and damage the cylinder block.

handle

When encountering piston knocking, the following methods can be used to handle it:

(1) After the engine starts, there is a knocking sound when running at low temperature. After the temperature is normal, the sound disappears and can be left untreated for now. Continue running.

(2) When the engine temperature is normal, there is a noticeable knocking sound, and high-speed operation should be avoided as much as possible, and disassembly and maintenance should be carried out as soon as possible.

(3) After removing the cylinder head and pulling out the piston, if the cylinder is found to be seriously out of round, strained, or the gap between the piston and the cylinder is too large, it should be replaced. Replace the cylinder liner, piston and piston ring.

(4) If deformation of the connecting rod is found, it should be replaced as much as possible.