Diesel engine repair is a complex repair technology, and engine repair workers must master it well, because the engine is the core of all machines. Once the engine fails, the diesel engine will not work. It can be seen how important engine repair technology is. So what are the common faults of diesel engines? And how to fix these common faults? Let's follow along and learn together!

The methods of repairing faulty diesel engines are as follows:

1. Diesel engine is difficult to start

(1) Check the low pressure oil circuit

① Check whether the diesel switch at the lower part of the diesel tank is turned on, and use the drain valve to drain the water and dirty oil in the diesel tank; check and remove the water and dirty oil in the diesel filter and filter.

② Loosen the bleed screw on the pump body of the high-pressure oil pump, pump oil with a manual pump, and check whether the supply of low-pressure oil is smooth and sufficient. If there is unclean air in the diesel fuel to be cleaned, check whether there is any air leakage in the pipeline in front of the manual pump, such as whether the gasket of the pipe joint is damaged, whether the pipe joint is tightened, whether the pipeline is damaged or cracked, etc. When pumping oil with a hand oil pump, if you feel that the oil is difficult to come in and the oil is not sucked smoothly, it means that there is a blockage in the low-pressure oil circuit, and you should check whether the filter screen of the diesel filter, the filter element of the diesel filter or the pipeline is blocked. When the temperature is low, check whether the diesel trademark is correct, and whether the oil circuit is blocked due to the wax precipitation of diesel oil or the freezing of water. Remove the blockage and stop when the oil suction is smooth and the oil is discharged without air bubbles.

③ When pumping oil with a manual pump, if the diesel cannot be pumped for the above reasons, it means that the piston of the manual pump is excessively worn, or the valve is cushioned or damaged by dirt, or the seal of the manual pump is damaged, and the manual pump should be replaced.

(2) Check the high pressure oil circuit

If there is no fault in the low-pressure oil circuit and it still cannot be started, check the working condition of the high-pressure oil circuit.

① Check whether the high-pressure oil pump oil volume adjustment gear rod is sensitive, whether it is stuck in the oil stop position, or cannot supply oil due to other forms of damage.

② Check whether the oil supply time of the high-pressure oil pump is correct. If the timing of fuel supply is incorrect, it should be adjusted to the standard timing.

③ Sweep the air in the high pressure oil pipe. If there is air in the diesel high-pressure oil pipe, it is sometimes difficult to remove the diesel engine by the starter to drive the diesel engine to roll, and the diesel engine is also difficult to start. To do this, loosen the bolts connecting each injector to the high-pressure fuel pipe, press the start button (or turn the start key to "start") and use the starter to drive the diesel engine to rotate until each high-pressure fuel pipe sprays fuel, and then tighten the high-pressure fuel pipe Attachment bolts.

④If the diesel engine still cannot be started so far, you should check whether the fuel injector and the high-pressure fuel pump are faulty. The main faults of the injector are burnout, poor atomization and incorrect adjustment of the injection pressure. The high-pressure oil pump mainly has faults such as the lack of oil supply pressure and the breakage of the speed regulating spring. It should be noted that the adjustment of the high-pressure oil pump must be carried out on the high-pressure oil pump test bench; the same is true for the injector, which must have a pressure tester.

2. The diesel engine emits white smoke during operation

(1) Check the water temperature

If the water temperature of the diesel engine is too low, the temperature in the combustion chamber of the diesel engine will be too low, and it is not easy to atomize and incinerate after the diesel fuel is injected. When the diesel engine is operating, when the water temperature is lower than 67°C, it is called cold state; the diesel engine operates in a supercooled state, which is very unfavorable for the service life, and measures should be actively taken to prevent the diesel engine from operating in a supercooled state. After the diesel engine is started, it should run at idle speed for 3-5 minutes, and then work with medium throttle and medium and small load to warm up the engine at slow speed. After the water temperature of the diesel engine reaches the green range of the water temperature gauge, work with the large throttle.

(2) Check and adjust the fuel injection advance angle

If the fuel injection early angle is too small, the diesel fuel cannot be atomized and burned after being injected, and the oil mist is brought out with the exhaust gas, and the smoke color is white or off-white.

(3) Check diesel quality

Poor quality diesel oil, or too much water content in diesel oil, will generate excessive water vapor during incineration, which will be discharged as white or gray-white smoke.

3. Black smoke when the diesel engine is working

(1) Check the air supply system

If the air intake of the diesel engine is insufficient, the amount of air entering the diesel combustion chamber is too small, the diesel fuel is not sufficiently burned, and some diesel fuel turns into carbon black particles under high pressure to form black smoke. At this moment, you should check whether the air filter element and the air intake are blocked; The working condition of the supercharger, whether the intake manifold is leaking; whether the valve phase is changed, whether the valve is correct, whether the intake and exhaust valve seats are leaking; whether the piston, piston ring, and cylinder liner are excessively worn and poorly sealed.

(2) Check the diesel supply system

The poor fuel supply of the diesel engine will lead to poor mixing. Even if the intake air is sufficient, it cannot be completely burned, thus causing black smoke. At this moment, you should check: whether the high-pressure oil pump is not adjusted properly, resulting in a large fuel supply; whether the oil outlet valve is not operating properly, causing Secondary injection or dripping of the fuel injector; whether the fuel injection pressure of the fuel injector drops, resulting in poor atomization, dripping fuel from the fuel injector, or insufficient fuel injection due to over-installed or missing fuel injector gaskets; Poor quality of diesel fuel causes poor combustion.

4. Deflagration of diesel engine

When the diesel engine deflagrates, the pressure in the cylinder increases suddenly, and the piston strikes the cylinder liner strongly, causing a loud metal knocking sound and oscillation.

(1) Check and adjust the advance angle of fuel supply: the advance angle of fuel supply is too large, and too much diesel is injected into the piston when the piston is near the top dead center, which causes the diesel pressure to rise rapidly, and makes the cylinder liner strongly strike when the piston goes down.

(2) Check the quality of diesel oil: If the quality of diesel oil does not meet the national standards and there are too many flammable components, it will cause deflagration when diesel is injected into the cylinder, resulting in excessive increase in the pressure in the cylinder and causing piston knocking.

(3) Check the overheating operation time of the diesel engine: the diesel engine is overheated for a long time, the temperature in the incineration room is too high, the diesel fuel is injected too fast, the combustion speed is too fast, and the pressure rises too fast, which causes deflagration.

(4) Removal of carbon deposits: Excessive carbon deposits in the cylinder liner and piston of the diesel engine cause the compression ratio to be too high and cause deflagration.

5. Troubleshooting for lack of diesel engine power

Diesel engines will inevitably encounter a lack of power during operation. Don't be overwhelmed when you encounter such a situation, and use the deletion method to determine one by one. The following points are some ways to check the lack of power for reference.

(1) Check for smoke and wear

When the engine is in operation, open the oil cap, if there is a thick smoke coming out of the oil cap, it is called smoke, and the phenomenon of smoke is serious, indicating that the piston, cylinder liner, piston ring and other parts are seriously worn.

Open the valve cover, if there is a trace of cyan or white smoke coming out from the root of the valve (valve working surface), it is called upper smoke, and the phenomenon of upper smoke is serious, indicating that the valve or valve seat is severely worn or ablated, or the valve The gap is too small to no gap. By investigating the smoke situation, you can directly see which valve and which cylinder is leaking and should be repaired in time.

(2) Look at the carbon deposits and check the working conditions

The carbon deposit at the exhaust port of the diesel engine is black and gray, and the outer surface is covered with a layer of hoarfrost. The carbon deposit layer is extremely thin, indicating that the diesel engine is in good working condition. The color of the carbon deposits is dark and bright, but not wet, which means that the diesel engine burns oil slightly and should be removed in time; if the thickness of the carbon deposits at the exhaust port of a certain cylinder is significantly higher than that of the exhaust ports of other cylinders, it means that the fuel injector of this cylinder is not working properly or the cylinder is sealed. If it deteriorates, it should be repaired or replaced; if a single exhaust port is wet or has organic oil, it means that there is a lot of oil in the cylinder and should be repaired; if the carbon layer of the exhaust port of each cylinder is thick and the color is darker, there are many reasons for this If the working temperature is too low, or the fuel injection is too late, and the diesel afterburning is severe, it should be used correctly and adjusted in time.

(3) Look at the water temperature and check the cooling system

If the water temperature of the cooling system is too high (over 100°C) when the engine is operating, it means that the scale in the cooling water cavity of the engine is too thick or the power of the cooling system related components (thermostat, water pump, fan, etc.) is low or ineffective.

(4) Check the valve timing and valve phase

After the engine has been operated for a long time, the timing gear, the surface of the cam, the follower column and the tappet will be worn out, so that the opening and closing time of the intake valve and the exhaust valve will be delayed backward, which will violate the optimal valve phase and reduce the charging power. Engine power drops. Therefore, it is necessary to regularly check the engine valve phase, and if it does not meet the requirements, it should be adjusted in time.

(5) Check the fuel injection and check the fuel injection pump. The fuel injection should not be deflected, not dripping oil, the oil mist should be uniform, and the range should be appropriate. During operation, you can hear a loud "flutter, buzz" sound, and you can feel the high-pressure oil pipe with your hand. There is a pulse. dynamic. Excellent fuel injection does not completely indicate that there are no problems with the oil circuit parts. Therefore, it is also necessary to check whether the oil supply rod and the fork are stuck and loose.

(6) Look at the burning, check sooner or later

Seeing the combustion refers to checking whether the fuel injection is timing, that is, whether the fuel supply advance angle meets the regulations. If the oil supply is too late (the early angle is too small), the diesel engine will be difficult to start, the combustion will not be complete, the exhaust gas will smoke, the engine temperature will be too high, and the power will be lacking; if the oil supply is too early (the early angle is too large), the diesel engine will be knocked during operation. It is easy to damage the parts, and it is easy to reverse when starting, and it will also be affected at the same time. to engine power.

(7) Look at the compression force and check for air leakage

Taking the S195 diesel engine as an example, the way to check the compression force is to shake the crankshaft without decompression. When the compression force is large, shake it upwards and release the crank handle but do not leave the crank handle. , if there is a large rebound force at this moment, it means that the compression force is very good; on the contrary, it means that the compression force is poor.

The reasons for the poor sealing performance of the cylinder: the valve has no gap or the gap is too small, the gap between the piston and the cylinder liner and the end face of the piston ring is too large, and carbon deposits in the ring groove, etc. When the engine is working, if you hear a "hissing" blowing sound near the air filter, it means that the leakage is related to the valve. At this point, the cause of the failure can be recognized in combination with the smoke condition.

(8) Look at the smoke, check the color of the smoke

When the engine is working normally, it generally does not emit smoke or emits some light gray-white smoke, which is sometimes difficult to see with the naked eye. If there is black smoke, it means that there is more oil and less gas in the cylinder, and the combustion is not complete; if there is blue smoke, it means that the wear gap between the cylinder liner and the piston, valve and valve guide is too large, and if there is white smoke, it means that the fuel is mixed with water , or the diesel oil is not completely incinerated and emerges from the exhaust pipe after gasification.

The above is the repair of common failures of diesel engines. You must read them carefully. The failure of diesel engines is a very fatal problem, which is directly related to whether the diesel engine can work normally. Therefore, everyone must pay attention to the engine repair technology, and study how to repair the failure of the diesel engine.