Causes of cracks in the body
In use, cracks are sometimes encountered in the body(especially the cylinder body, cylinder head) for the following reasons:
(1) manufacturing defects. For example, trachoma, shrinkage, stomata, etc., as well as poor aging, stress concentration areas and other quality defects caused by the body cracks.
(2) Inappropriate use. For example, in the high temperature and lack of water in the engine, a large amount of cold water is suddenly added; When Yandongjijie starts in the morning, add a lot of high warm water; Start the engine first, add cold water after the temperature rises; In the winter, no antifreeze was used, and the parking time was longer. The cooling water was not released, resulting in the freezing of the cooling water.
(3) Improper maintenance and repair. Failure to tighten the main and secondary bolts as required; Replacement.
Too much excess of self-made water; Due to the lack of dedicated maintenance tools, the fuselage is cracked when it is turned over. In the use and maintenance, we should pay attention to the above problems to prevent the failure of the cylinder body crack.
2 Engine crankshaft fracture analysis
Crankshaft fracture is a serious mechanical failure of the engine. Fracture usually occurs in the stress concentration of the crank pin and the connection of the spindle neck with the crank arm or the oil hole of the shaft neck.
Main Causes of Crankshaft Fracture
(1) Due to the improper use of oil by individual users, or the cleaning and replacement of "three filters", the oil is deteriorated for a long time; Severe overload and overhang caused the engine to be overloaded for a long time and there was a tile burning accident. The crankshaft was badly frayed by the engine's brazing. The WD615 series engine crankshaft is replaced and repaired, that is, a new crankshaft machine is purchased, which will damage the crankshaft and send it to the manufacturer for repair. After the problem of crankshaft wear occurred in some users, due to cost and time considerations, some small factories were found in the local area to repair and process the severely worn crankshaft for welding, processing, and grinding after overall heat treatment. Due to repair methods and technical problems, the joint angle of crank pin and spindle neck and crank arm has changed, resulting in local stress concentration; Since the crankshaft is refined 45 steel die forging, the welding has changed the gold phase of the curved car. The above two are the main causes of crankshaft fracture.
(2) After the engine is repaired, the loading vehicle does not go through the grinding period, that is, overload overhang, and the engine is overloaded for a long time, so that the crankshaft load exceeds the allowable limit.
(3) The use of overwelding in the repair of the crankshaft has damaged the dynamic balance of the crankshaft, and has not been balanced and verified. The uneven measurement has exceeded the standard, causing a large vibration of the engine and causing the crankshaft to break.
(4) Due to poor road conditions and seriously overloaded vehicles, the engine is often at the critical speed of torsion and the shock absorber fails, which will also cause the crankshaft to twist vibration fatigue and break.
31 Causes of early wear of engine cylinder cases
The engine cylinder wear over the allowed standard will make the vehicle's power and economy seriously reduced. Therefore, to understand the cause of cylinder sleeve wear, holding the wear rules of the cylinder, easy to use correctly, to slow down the cylinder wear, extend the service life of the engine.
Wear regularity of cylinders
The wear and tear of the WD615.67 engine cylinder in use is uneven. The general rule is that along the axis of the cylinder, the upper part of the cylinder sleeve, the first ring is slightly below the top point of the wear, the piston ring below the bottom point of the minimum wear. From the worn cross section, the cylinder is ground into a non-standard cylinder. In general, the wear of the first cylinder and the sixth cylinder of the engine is more serious than that of other cylinders. The main reason is due to poor cooling.
Causes of engine cylinder wear
That is, mechanical wear, abrasive wear, chemical corrosion.
(1) Mechanical wear:
Mechanical wear is caused by mechanical friction. The degree of mechanical wear is affected by the machining accuracy, quality, lubrication conditions, working temperature, and mutual pressure in the friction of the cylinder and piston ring. When the engine is working, the upper temperature is high, the lubricating oil is thinned by the influence, the quality of the oil film is poor, and the back pressure of the first piston ring(high-pressure gas enters the piston ring slot, pressing the piston ring tightly on the cylinder wall) is the largest. Therefore, The first piston ring at and slightly below the upper part of the cylinder is the most worn, while the lower part of the cylinder is less worn.
(2) Abrasion of abrasives
Abrasive wear is the most important wear. Abrasives are made by mixing the metal impurities mixed in the oil with the impurities brought into the air. It can accelerate the wear of the parts. Due to the intake process, the pressurized air intake directly rushed into the cylinder wall opposite the intake valve. When the engine was operating at a low temperature, the diesel spray was poor, and the diesel oil particles that could not be fully burned diluted the oil and thinned the oil. Destroyed the oil film. At the same time, due to the damage of the air filter filter core, the dust and sand grains brought into the air intake adhere to the cylinder wall opposite the air intake door, resulting in severe abrasion. Abrasive wear not only causes a large wear on the upper end of the first piston ring of the cylinder, but also makes the cross section of the cylinder Oval. The main causes of abrasion are: damage to the air filter filter core, falling off, cracking or disconnecting the rubber pipe from the Supercharger to the medium cooler or the Supercharger to the intake pipe connection, and air short-circuit into the cylinder to form serious abrasion; There are also some users who place excessive emphasis on the replacement of oil by quality, the use of oil is too long, the oil is spoiled, thinning, and impurities are increased, and metal impurities are mixed to cause serious abrasion. In units where laboratory equipment is not yet available, it is still best to implement periodic oil replacement. Each secondary maintenance(12,000 km) replacement of oil and oil filter core, air filter core is the best maintenance method.
(3) Chemical corrosion
When the temperature of the cylinder wall is low and the pressure in the cylinder is large, the water vapor in the cylinder will form water beads on the cylinder wall. These beads and exhaust gas contact to form an acidic material, attached to the cylinder wall, causing corrosion to the cylinder. The lower the temperature of the cylinder, the easier the acid is to form, and the greater the corrosion effect. Corrosion wear is mainly due to improper operation. The correct operation is that after the starter is launched, the idle speed is operated for a few minutes. After the water temperature and oil pressure are normal, the engine speed is gradually increased to keep the engine temperature normal. The engine water temperature is 80 ~ 90 °C during driving. Low temperature driving is very unfavorable to the engine, and corrosion and wear are also increased.
In order to ensure the normal operation of the engine and prevent the early wear of the cylinders, the following suggestions are put forward:
(1) After the engine is started, it runs idle for a few minutes. After everything is normal, the engine's speed is increased, the load is increased, the normal operating temperature of the engine is maintained, and the low-temperature driving is resolutely eliminated.
(2) Clean the air filter filter in time, and replace it in time if it is damaged; It is best to replace the air filter filter core each time the second guarantee(running 12,000 kilometers).
(3) Ensure the use of qualified CD grade medium-charged diesel engine oil and implement scheduled oil change to ensure the cleanliness and quality of oil. Two oil change and oil filter at a time.
(4) Always check the Supercharger to the Intercooler and the connecting part of the intake pipe to prevent the connection hose from receding and breaking, and ensure that the air is filtered into the cylinder.
In short, pay attention to the correct operation and maintenance, pay attention to the use of the vehicle running period, the early wear of the cylinder can be effectively prevented.
Causes and treatment of excessive wear of 4 cylinder sleeve
Due to the different position of the piston, the working conditions are different, and the wear of each part of the cylinder sleeve is also different. The wear of the cylinder sleeve is the most serious with the first piston ring and the contact part of the cylinder wall. From top to bottom, the wear amount is significantly reduced. This large and small wear makes the cylinder a conical shape. If there are impurities in the oil that are not filtered by the filter, impurities and metal chips in the oil are brought to the surface of the cylinder wall, abrasion is produced, and the cylinder sleeve becomes waist drum after wear.