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Common Truck Engine Overhaul And Repair Methods

For truck drivers, working outside all year round, they will inevitably encounter problems with their own vehicles. Therefore, it is very necessary to understand some basic engine maintenance knowledge.

1.Cause Analysis Of Body Cracks

In use, cracks sometimes appear on the engine block (especially cylinder block and cylinder head), which are caused by the following aspects:

Manufacturing defects. Such as sand holes, shrinkage porosity, pores, etc., as well as body cracks caused by poor aging, stress concentration areas and other quality defects.
Improper use. If a large amount of cold water is suddenly added under the condition of high temperature and water shortage of the engine; When starting in the morning of severe winter season, add a large amount of high-temperature water; Start the engine first and add cold water after the temperature rises; The antifreeze was not used in winter, the parking time was long.
Improper maintenance and repair. Failure to tighten the main bolts and auxiliary bolts as required; Interchangeable
The interference of self-made water plugging is too large; Due to the lack of special maintenance tools, the fuselage is cracked when it is overturned. During use and maintenance, pay attention to the above problems to prevent the occurrence of cylinder crack fault.

2. Engine Crankshaft Fracture Analysis Of Engine Overhaul

Crankshaft fracture is a serious mechanical failure of engine. The fracture usually occurs in the stress concentration parts such as the connecting fillet between crank pin, main journal and crank arm or journal oil hole.

Main causes of crankshaft fracture

Due to improper selection of engine oil or careless cleaning and replacement of “three filters”, the engine oil has deteriorated for a long time; Serious overload and over hanging cause the engine to overload for a long time and cause tile burning accident. The crankshaft is severely worn due to engine Bush burning. The crankshaft of WD615 Series engine is repaired by replacement, that is, a new crankshaft is purchased and installed, and the damaged crankshaft is sent to the manufacturer for repair and standby. After the problem of crankshaft wear occurred in the vehicle, some users found some small factories to repair and process.
After the engine is repaired, the loading does not go through the running in period, that is, overload and overload. The engine runs overload for a long time, so that the crankshaft load exceeds the allowable limit.
Surfacing welding was used in the repair of the crankshaft, which damaged the dynamic balance of the crankshaft and did not do balance verification. The imbalance exceeded the standard, causing greater vibration of the engine and fracture of the crankshaft.
Due to poor road conditions and serious overloading of vehicles, the engine often operates at the critical speed of torsional vibration, and the failure of shock absorber will also cause torsional vibration fatigue damage and fracture of crankshaft.

3. Causes Of Early Wear Of Engine Overhaul

If the engine cylinder wear exceeds the allowable standard, the power and economy of the vehicle will be seriously reduced. Therefore, understand the causes of cylinder liner wear and hold the wear law of the cylinder, which is convenient for correct and reasonable use, so as to slow down the wear of the cylinder and prolong the service life of the engine.

Wear law of cylinder

WD615. 67 the wear of engine cylinders in use is uneven. The general rule is that along the axis direction of the cylinder, above the cylinder liner, the wear amount of the first gas ring is the largest slightly below the top dead center, and the wear of the piston ring is the smallest below the bottom dead center. From the wear cross section, the cylinder is ground to non-standard cylindricity. Generally, the wear of the first and sixth cylinders of the engine is more serious than that of other cylinders, which is mainly caused by poor cooling.

Causes of engine cylinder wear

Mechanical wear, abrasive wear and chemical corrosion.

(1) Mechanical wear:

Mechanical wear is caused by mechanical friction. The degree of mechanical wear is affected by the machining accuracy, matching quality, lubrication conditions, working temperature and mutual pressure in friction of cylinder and piston ring. When the engine is working, the upper temperature is high, the lubricating oil becomes thinner due to the influence, and the quality of the oil film is poor. The back pressure of the first piston ring (high-pressure gas enters the piston ring groove and tightly presses the piston ring on the cylinder wall) is the largest. Therefore, the wear of the first piston ring and slightly lower part of the cylinder is the largest, while the wear below it becomes smaller.

(2) Abrasive wear:

Abrasive wear is the most important wear. Abrasive is made of metal impurities mixed in engine oil and impurities brought into the air, which can accelerate the wear of parts. During the intake process, the pressurized intake flow directly rushes into the cylinder wall opposite to the intake valve. When the engine is running at low temperature, the diesel spray is not good enough, and the diesel oil particles that are not fully burned weaken the oil, causing the oil to dilute and damage the oil film.

At the same time, due to the damage of the air filter element, the dust and sand brought by the inlet flow adhere to the cylinder wall opposite the inlet valve, forming serious abrasive wear. Abrasive wear not only causes large wear at the slightly lower part of the top dead center of the first piston ring in the upper part of the cylinder, but also makes the cross section of the cylinder become oval. The main causes of abrasive wear are: the filter element of the air filter is damaged, the rubber hose from the supercharger to the intercooler or from the supercharger to the intake pipe falls off, cracks or breaks, and the air is short circuited into the cylinder, resulting in serious abrasive wear; Some users put too much emphasis on changing the engine oil according to the quality. The best maintenance method is to change the oil, oil filter element and air filter element every secondary maintenance (12000km).

(3) Chemical corrosion:

When the engine cylinder wall temperature is low and the pressure in the cylinder is high, the water vapor in the cylinder will form water droplets on the cylinder wall. These water droplets contact with the exhaust gas to form acidic substances, which are attached to the cylinder wall and corrode the cylinder. The lower the working temperature of the cylinder, the easier the formation of acidic substances and the greater the corrosion. Corrosion and wear are mainly caused by improper operation. The correct operation should be that after the starter is started, run at idle speed for several minutes. After the water temperature and oil pressure are normal, gradually increase the engine speed to keep the engine temperature normal. During driving, the engine water temperature should be 80 ~ 90 ℃. Low temperature driving is very unfavorable to the engine, and the corrosion and wear are also increased.

In Order To Ensure The Normal Operation Of Engine Overhaul And Prevent Early Wear Of The Cylinder, The Following Suggestions Are Put Forward:

After the engine is started, run at idle speed for several minutes. After everything is normal, increase the engine speed, increase the load, maintain the normal working temperature of the engine, and resolutely eliminate low-temperature driving.
Clean the air filter element in time, and replace it in time if it is damaged; It is best to replace the air filter element every time the second guarantee (12000km operation).
Ensure the use of qualified CD grade medium supercharged diesel engine oil, and change the oil on schedule to ensure the cleanliness and quality of the oil. Change the oil and oil filter every time.
Frequently check the connecting parts from the supercharger to the intercooler and to the air inlet pipe to prevent the connecting hose from loosening and cracking, and ensure that the air enters the cylinder after filtration.
In short, pay attention to the correct operation and maintenance, pay attention to the use of the vehicle during running in period, and the early wear of the cylinder can be effectively prevented.

4. Causes And Treatment Of Excessive Wear Of Engine Overhaul

Due to different piston positions and working conditions, the wear of each part of the cylinder liner is also different. The wear of cylinder liner is the most serious at the contact part between the first piston ring and cylinder wall. From top to bottom, the wear amount is significantly reduced. This kind of wear from top to bottom makes the cylinder conical. If there are impurities in the engine oil that are not filtered by the filter, the impurities and metal chips in the engine oil are brought to the cylinder wall surface, resulting in abrasive wear. After wear, the cylinder liner becomes waist drum.
The cylinder liner of Steyr WD615 Series diesel engine is dry, and the quality of cylinder liner is excellent, but some users report that the cylinder liner is worn too much.

The serious wear of the engine cylinder liner is caused by the following reasons:

Filter failure. In particular, the air filter is broken and the air is short circuited into the cylinder without filtering. As the dust and impurities in the air enter the cylinder, the wear of the cylinder liner is intensified.
The wrong brand of engine oil causes poor lubrication and serious wear of cylinder liner.
The use of inferior diesel fuel causes serious coking after combustion, resulting in serious wear of cylinder liner.
Operational problems. Cold start, especially in winter, due to the high viscosity and poor fluidity of the oil, the oil supply of the oil pump is insufficient; At the same time, the oil on the original cylinder wall flows down along the cylinder wall after stopping, and can not get the same lubrication at the moment of starting, which increases the wear of the cylinder wall.
Low temperature driving. Because the temperature is too low, good lubrication can not be maintained, which increases the wear of the cylinder.
Quality and assembly of cylinder liner.

To Prolong The Service Life Of Engine Overhaul, The Following Work Must Be Done:

Start the engine correctly. In order to increase lubrication and reduce wear, when starting the engine for the first time, it is advisable to use the starter to drive the engine to idle for several revolutions, and then supply oil for starting after the friction surface is lubricated. After starting, operate at idle speed (650 ~ 700R / min) for 3 ~ min, the standby oil pressure is normal, and the water temperature reaches 40 ℃. Start with low gear and drive slowly for about one kilometer, and then gradually return to speed after the oil pressure and water temperature are all normal.
Maintain the normal temperature of the engine. When the temperature is low, the water vapor in the cylinder is easy to condense into water droplets. After the water droplets dissolve the acid gas molecules in the exhaust gas, they are easy to generate acidic substances, which will corrode the cylinder; High temperature reduces the strength of cylinder liner and increases wear. The normal water temperature of the engine shall be maintained at 80 ~ 90 ℃.

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