1) The clearance between piston and cylinder is too small
The clearance between the piston and the cylinder should be strictly in accordance with the instructions of the diesel engine manual. If the clearance is too large, it will be difficult to cold start the diesel engine. When the engine is cold, it will make a knocking sound and the power will drop. If the gap is too small, it will cause failures such as pulling cylinder and expanding cylinder.
Especially when the coefficient of linear expansion of the aluminum alloy used in the piston is relatively large, the above-mentioned situation is more likely to occur. When the diesel engine is repaired, if there is no instruction manual for the engine. Refer to the matching clearance of similar models. The matching clearance of air-cooled diesel engines is generally slightly larger than that of water-cooled ones. Normally, for a four-stroke water-cooled diesel engine with a cylinder diameter of 100 mm, when using aluminum pistons, the fit clearance is 0.120 to 0.150 mm.
2) The gap of the piston ring opening is too small
The gap and backlash of the piston ring are too small, the friction force between the ring and the cylinder wall is too large, the carbon deposit in the cylinder is serious, and the dirt or oil is not clean during assembly, causing strain.
The gap of the opening of the piston ring is too small. After the old cylinder is replaced with a new ring, the first air ring hits the shoulder of the cylinder liner or the opening of the piston ring expands too much during assembly, which may cause breakage.
The backlash is too small, no special tools are used when disassembling, making the ring spiral, causing an elastic effect or serious carbon deposits in the cylinder, will cause the piston ring to bite.
Piston ring opening clearance and side clearance are too large, twisted ring and conical ring are installed upside down, and dirty oil makes the oil passage hole clogged.
Piston ring opening gap is too small, impact at the opening; side gap is too large, the ring hits the ring bank; the old cylinder is replaced with a new ring, the first air ring hits the shoulder of the cylinder sleeve, etc. These conditions will cause noise.
3) The piston ring is broken
The deflection of the piston in the cylinder is too large, resulting in ellipse and taper, and there is a step on the upper part. The working surface of the inner wall of the cylinder liner often forms uneven wear in the movement area of the piston ring. Grinding into an irregular oval in the direction.
At the position where the cylinder liner wears the most, the ellipticity tends to be the largest. The parts where the cylinder liner and the piston ring are not in contact do not wear out, so obvious wear steps appear. The gas pressure during the power stroke forces the piston to move to the bottom dead center, which is converted from reciprocating. In order to rotate, the pressure of the piston ring on the side of the cylinder liner is the largest in the direction of the crank movement plane, which causes the cylinder liner to wear, that is, the cylinder liner perpendicular to the direction of the crankshaft wears the most, the crankshaft bends, the connecting rod bends, the center line of the cylinder liner and the crankshaft The line is not vertical, and the axial clearance of the crankshaft is too large, which can cause the piston ring and the cylinder liner to be unevenly worn and unevenly broken.
If the clearance of the bearing bush is too large, the clearance of the piston pin and the connecting rod copper sleeve is too large, and the first gas ring is most likely to break when there is a significant wear step on the upper part of the cylinder liner. Stuck on the piston, or the piston pin retainer snapped off or fell off.
4) The piston and piston ring are tilted to one side and pressed tightly against the cylinder wall;
Due to the deformation of the piston, the deviation of the piston hole, the deflection of the cylinder honing, the bending or twisting of the connecting rod, the unbalance of the crank pin and the main journal, the pressure on the cylinder wall of the piston is relatively concentrated, and the local surface makes the The oil film between them becomes thin and even ruptures under great pressure, thereby losing the lubricating effect and forming dry friction to cause the cylinder to pull.
5) Poor atomization of fuel injector (carburetor) for a long time
Fuel injection nozzle is the most precise component, the engine mainly burns gasoline when working. Due to the high temperature during the combustion process, carbon deposits are generated on the surface or pores of the fuel injection nozzle and at the same time, more colloid will also be deposited on the inner wall of the fuel injection nozzle and the surface of the needle valve in long-term use, which affects the fuel injection effect and makes the fuel injection nozzle Blockage and adhesion cause leakage of fuel injection, poor atomization, or even no fuel injection, resulting in increased fuel consumption, decreased engine power, unstable idle speed, poor acceleration, and difficulty in cold starting. The test data indicates that when 10% of the fuel injection volume is blocked, it will cause incomplete combustion of the engine, reduced performance, increased fuel consumption and increased exhaust temperature. At this time, the fuel injector should be cleaned in time to improve the combustion efficiency of the engine.
6) Malfunction of the piston cooling nozzle.
Individual engines are cooled by engines that rely on connecting rod bearings to lead to piston pins and piston oil injection nozzles to inject oil. Due to various reasons, the fuel injection cannot be performed normally, causing the piston top to overheat, causing the piston top to melt and pull the cylinder. (The role of engine oil: cooling, lubrication, cleaning, sealing, (anti-rust)
7) Poor engine cooling and supercooled operation
Engine running at a water temperature below 65 ° C is called cold running. The engine will not start running until the water temperature reaches a certain level, or when the thermostat opening temperature is too low, the cooling water will enter the large cycle prematurely, which will cause supercooling. When the cylinder wall temperature drops from 800 ° C to 500 ° C, the wear of the cylinder liner increases about 5 times. When the cylinder wall temperature reaches 80 ° ~ 850 ° C, the amount of wear is significantly reduced. If the water temperature is too low, diesel will rise slowly at the combustion room temperature, the lag period will be long, the combustion process will deteriorate, and the running performance will be poor.
