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[Lubrication Analysis] Failure Analysis of Engine Lubrication System

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[Abstract]:
The function of the engine lubrication system is to lubricate, clean, cool and seal the friction components.

The function of the engine lubrication system is to lubricate, clean, cool and seal the friction components. The lubrication system consists of an oil filter, an oil pump, a pressure limiting valve, an oil filter, an oil line, and an oil passage. It has common faults such as excessive oil pressure, low oil consumption, excessive oil consumption and engine oil deterioration.

Oil pressure is too high

1. Fault phenomenon

(1) When the cold car is started, the oil gauge indicates a pressure of about 0.5 MPa;

(2) Turn on the ignition switch, the oil gauge indicates a pressure of about 0.2 MPa, and increases to about 0.5 MPa or more after starting;

(3) When the engine is running, the oil pressure suddenly increases.

2. cause of issue

(1) The viscosity of the oil is too large;

(2) improper adjustment of the pressure limiting valve;

(3) There is blockage in the lubricating oil passage of the cylinder block;

(4) The clearance of the main bearing or connecting rod bearing is too small;

(5) The oil filter element is clogged and the bypass valve is difficult to open;

(6) The oil pressure gauge or its sensor is invalid.

3. Failure analysis

(1) When the oil pressure is too high, first check if the viscosity of the oil is too large, and if the pressure limiting valve is improperly adjusted (the spring is adjusted too hard). For new engines, check if the clearance between the main bearing, the connecting rod bearing or the camshaft bearing is too small;

(2) When the oil pressure suddenly increases, first check if the oil filter element is dirty and the bypass valve spring pressure is adjusted too much. If it is good, it is generally blocked in the lubrication system oil passage. After the camshaft timing gear is broken, the debris is easy to block the oil passage, so it must be cleaned;

(3) Turn on the ignition switch, if there is pressure indication on the oil gauge, check whether the oil gauge and sensor are in good condition.

Oil pressure is too low

1. Fault phenomenon

(1) When the engine is running, the oil pressure is always too low; (2) After the engine is started, the oil pressure is quickly lowered.

2. cause of issue

(1) insufficient oil in the oil pan;

(2) The viscosity of the oil is small;

(3) The pressure limiting valve is improperly adjusted, the spring is broken or the elastic force is insufficient;

(4) The oil filter bypass valve is not sealed or its spring is broken and the elastic force is insufficient;

(5) The oil inlet pipe joint is loose or the oil pipe is broken;

(6) The oil pump is in poor working condition;

(7) The oil filter is clogged;

(8) The clearance between the main bearing of the crankshaft, the connecting rod bearing or the camshaft bearing is too large;

(9) The oil pressure gauge or sensor is invalid.

3. Failure analysis

(1) When the oil pressure is always too low, first pull out the oil dipstick and check if the oil is sufficient. If it is not enough, it should be added according to the standard; if it is sufficient, it should be checked whether the oil meter or sensor is invalid, and the failure must be replaced. After the change, the pressure is still too low, the sensor should be removed. If the oil is sprayed out in a short time, check the oil filter bypass valve, pressure limiting valve, oil inlet pipe, filter and oil pump, etc. ;

(2) When the engine is just working, the oil pressure is normal. After a period of operation, the oil pressure drops rapidly, indicating that the oil in the oil pan is insufficient or the viscosity of the oil is too small.

(3) During engine operation, the oil pressure drops suddenly, and should be stopped immediately to stop the fire, check the oil for serious leakage. This type of failure can occur, for example, when the oil filter gasket is damaged.

 

Excessive oil consumption

 

 

1. Fault phenomenon

The oil consumption exceeds 0.1~0.5L/100km.

2. cause of issue

(1) The gap between the piston and the cylinder wall is too large;

(2) The piston ring is worn too much or the elasticity is insufficient;

(3) The piston ring end gap, backlash and backlash are too large;

(4) Each piston ring is opposite;

(5) twisted ring reversed;

(6) The intake valve duct wears too much;

(7) Poor ventilation of the crankcase;

(8) The timing gear chamber is poorly sealed;

(9) The front and rear oil seals of the crankshaft are poorly sealed;

(10) The oil return hole of the main bearing cover after the crankshaft is too small;

(11) oil leakage after the camshaft;

(12) The oil pan or the valve chamber cover leaks oil.

3. Failure analysis

(1) Check for oil leaks. Among the main oil leakage parts, special attention is paid to oil leakage in front of and behind the crankshaft. Oil leakage at the front end is often caused by damage to the oil seal, aging, or excessive wear of the contact surfaces between the crankshaft pulley and the oil seal. In addition to the poor oil seal after the rear oil leakage, for the engine without the rear oil seal, it should also check whether the oil return hole of the main bearing cover is too small, and whether the oil plug at the rear end of the camshaft leaks oil;

(2) Check if the oil is sucked into the combustion chamber. When the throttle is increased to increase the engine speed, if the exhaust pipe discharges a large amount of blue smoke, and the engine oil port is heavily smoked or pulsating. The piston rod set should be removed for inspection and analysis, especially the end gaps, backlashes and backlashes of the first oil ring. If their clearance is too large, the oil will easily enter the combustion chamber;

(3) Check the ventilation of the crankcase. Poor ventilation of the crankcase will increase its internal gas pressure and oil temperature. The increase in gas pressure not only causes oil leakage and evaporation, but also causes the oil pan liner or the valve chamber side cover gasket to be damaged. Therefore, poor ventilation of the crankcase is also a major cause of excessive oil consumption.