Basic Knowledge About Engine

1. How to start the main engine oil pump?

A: Generally, after the main engine is shut down, the inlet valve of the oil pump is open (the oil is hot). After a long period of shutdown, the oil cools and its viscosity increases. To avoid overloading the pipes and motor, the opening pressure of the pressure regulating valve on the oil pump should be reduced before starting the pump with cold oil; the bypass valve of the oil cooler should also be opened slightly. When starting the oil pump, pay attention to the pressure gauge reading and gradually increase the opening pressure of the pressure regulating valve to the allowable load of the motor, until the pressure regulating valve is adjusted to the normal opening pressure. At this point, the oil pressure gauge reading will gradually rise and stabilize within the normal oil pressure range, indicating the oil pump starting operation is complete. When the ambient temperature is low, the oil should be heated and kept warm when the engine is parked.

2. What role does the lubricating oil play in pressure lubrication? What should the temperature and pressure range of the lubricating oil entering the bearing be during normal diesel engine operation?

A: When pressurized lubricating oil circulates in a diesel engine, it plays several roles, including lubrication, cooling, flushing, airtightness, vibration damping, and rust prevention. Lubrication and cooling are its primary functions. Flushing refers to the removal of impurities and metal shavings from bearings by the pressurized lubricating oil; airtightness refers to the sealing effect of the oil film adhering to the cylinder walls.

Different engine models have specific operating ranges for lubricating oil pressure. The lubricating oil pressure is determined based on its ability to reach the friction surfaces to be lubricated. The normal operating pressure of diesel engine lubricating oil is generally between 0.15 and 0.39 MPa. To ensure lubrication of the furthest and highest friction surfaces in the diesel engine, the operating pressure should not be lower than the lower limit of the normal value, but the lubricating oil pressure should not be too high either. Excessive pressure increases the burden on the oil pump, wasting power, and makes the joint surfaces prone to leakage. Furthermore, the large amount of lubricating oil escaping from the bearing clearances forms fine droplets that are easily oxidized and deteriorated in the crankcase, increasing oil consumption. The temperature of the lubricating oil should generally be between 45 and 75°C. Too low a temperature results in poor lubricating oil flow and increased power consumption by the oil pump; too high a temperature reduces oil viscosity, affecting lubrication performance, reducing cooling of high-temperature and friction components, and promoting oil oxidation and deterioration. Excessive oil temperature also poses a risk of detonation.

3. What are the causes of bearing overheating during diesel engine operation? How to check? What measures should be taken if overheating is observed?

Answer: The main causes of bearing overheating are:

1) Insufficient lubricating oil pressure, leading to insufficient bearing lubrication.

2) Metal powder or impurities mixed in the lubricating oil, clogging oil holes or oil grooves; severely deteriorated lubricating oil with increased acid value, resulting in poor lubrication and damage or corrosion of the bearing surface.

3) Damaged oil pipes or pipe joints causing severe oil leakage and insufficient oil supply.

4) Improper bearing clearance and excessive journal ellipticity, affecting oil film lubrication.

5) Improper tightening of bearing bolts, causing bearing deformation and disrupting normal lubrication.

6) Overloaded operation of the cylinder for excessively long periods.

Whether a bearing is overheating during operation can be determined by touching the outside of the crankcase, or by smelling oil or white smoke emanating from the safety port or inspection port.

If overheating of the bearing shell is detected, immediately reduce the speed and minimize the load. Increase the amount of lubricating oil and recheck the oil pressure and temperature to determine the cause. In this situation, do not abruptly stop the machine or open the crankcase door for inspection. Abruptly stopping the machine could cause the bearing to seize up. If increasing the amount of lubricating oil does not worsen the bearing overheating, stop the machine immediately and allow it to cool completely before opening the crankcase door for inspection. Otherwise, fresh air entering the crankcase and mixing with the hot oil and gas could cause a fire or explosion; this must be taken very seriously.

Once the overheating bearing is identified, it should be repaired or replaced according to the extent of the damage. If the connecting rod bearing is damaged and no spare part is available, the connecting rod of that cylinder should be removed and sealed, and the machine should be operated at a reduced speed.