First, the type of rattling and the cause
(A) the type of rattling.
Engine rattling is an abnormal sound produced by the engine, mainly mechanical rattling, combustion rattling and aerodynamic rattling.
(B) the cause of rattling.
(1) mechanical rattles. Mechanical rattles is mainly the movement with too large a gap or with surface damage, caused by impact and vibration during operation. (2) combustion noise. Combustion noise is mainly caused by abnormal engine combustion. (3) aerodynamic noise. Aerodynamic rattling is mainly in the engine intake, exhaust and operation of the fan, caused by airflow vibration.
Second, the influence of rattling factors and diagnostic conditions
(A) speed.
In general, the higher the speed, the stronger the mechanical noise. Nevertheless, but the high speed when a variety of loud mixed together, diagnosis of certain abnormal noise is not easy to identify. Therefore, the diagnostic speed is not necessarily high speed, to specific rattles specific treatment. Such as diagnostic valve ringing and piston knocking cylinder, at idle or low speed can be heard very clearly; when the main bearing ringing, connecting rod bearing ringing and piston pin ringing is more serious, at idle and low speed can be heard. In short, the diagnosis of different response in the most obvious sound of the speed, and try to carry out at low speed.
(ii) temperature.
Some of the noise and engine temperature, in the mechanical noise diagnosis, for the coefficient of thermal expansion of the fit vice to pay special attention to the thermal condition of the engine.
(iii) load.
Many rattles are related to the engine load. Such as the crankshaft main bearings, connecting rod bearings, piston knocking, cylinder leakage, etc., with the load increase and enhancement, with the load reduction and weakening; diesel engine fire knocking sound with the load increases and decreases.
Third, the diagnostic method of engine noise
(A) diagnosis by auscultation.
Auscultation refers to the use or not using a simple apparatus, the method and form of diagnosis of abnormal noise. Usually includes external auscultation and internal auscultation two kinds. (1) external auscultation. The use of stethoscopic instruments (metal rods or spinners, etc.) or not use stethoscopic instruments in the engine outside the way of auscultation, known as external hearing. There are real listening and virtual listening points, real listening is to use the stethoscope against the engine body for diagnosis of a diagnostic method, virtual listening is not to use the stethoscope to diagnose directly by hearing a method of diagnostic hearing. (2) internal auscultation. Internal auscultation is relative to the external auscultation, it is the use of sound-conducting equipment from the engine to pick up the sound of a way of auscultation. Such as the use of aural tube from the oil filler or oil dipstick socket inserted into the crankcase (can not be inserted into the oil pool) for auscultation. This way of auscultation can exclude the interference of external noise, especially for the weaker and difficult to identify the external diagnosis of abnormal noise, internal auscultation than the external auscultation of the effect is good.
(ii) the use of engine rattles with its speed changes in the characteristics of the diagnosis.
Because of the engine rattling parts of the structure of the form, bear the load, the location, lubrication conditions and the degree of looseness and so on, and thus produce rattling when the rotational speed is also different. Engine rattles have their own specific vibration frequency, when the movement speed frequency is an integer multiple of the rattling frequency, will produce resonance phenomenon, rattling intensified. That is, each kind of rattling in its most obvious sound corresponds to a movement speed band (speed range), generally will be the volume, rhythm, tone, etc. exposed to the most obvious speed or speed of the region known as the best diagnostic speed.
(C) the use of engine rattles with its load changes in the characteristics of the diagnosis.
Certain rattles during engine operation are related to the load of the engine. In general, the greater the load, the greater the rattling, which is manifested in the rattling and cylinder position has a clear relationship. In the diagnostic process, you can change the engine load, so that the sound size of the rattles changed, thus helping the rattles of the qualitative and positioning diagnosis. The method of changing the engine load has two practices: increasing the load and unloading the load. The one with more applications is to release the load. Unloading. The method is usually cylinder by cylinder cut off the fire or oil.
(d) the use of the maximum vibration part of the rattle for diagnosis.
Engine rattles, a part of the engine will produce vibration, its vibration frequency and rattling sound frequency is often the same. Because of the different parts of the rattling parts are different, so the engine vibration is not the same degree of intensity, usually the largest amount of vibration in the engine body on the region known as the maximum vibration parts, a variety of rattles in the engine body corresponds to the maximum vibration of their respective parts. According to this reasoning, you can roughly determine the part of the rattling parts, which is an important auxiliary means of diagnosing engine rattles. Therefore, by listening to the maximum vibration part, according to the maximum vibration part of the area on the cylinder block and the vibration frequency and the relationship between the rattles, you can roughly identify the parts of the rattles.
(E) the use of engine rattles with temperature changes in the characteristics of diagnosis.
Changes in engine operating temperature, can make the engine parts of the lubrication conditions and clearance changes. The higher the temperature, the lower the viscosity of the lubricating oil, the lubricating oil film between the rattling parts of the thinner, the greater the impact between the parts will be, the rattling sound is also more obvious; some rattling in the engine temperature, due to the different materials with the parts of the different heat expansion, rattling due to the increase in engine temperature to reduce, or even disappeared; this shows that some of the rattling of the engine and the temperature has a close relationship. Therefore, in the process of diagnosis and listening to the engine rattles, pay close attention to the relationship between rattles and temperature changes, cold, hot car comparison, is often one of the key basis for judging some rattles.
(F) the use of separate stopping? Motive accessories for diagnosis.
If you suspect that the generator, water pump, air compressor and other rattling, you can do a stopping test.
(G) according to other reference factors for diagnosis.
Some of the engine noise is often accompanied by a reduction in oil pressure, plus the oil port pulsating smoke, smoke from the exhaust pipe smoke colour is not right, power reduction, fuel consumption is too much and other faults. For example, the crankshaft bearings are too loose sound, often accompanied by reduced oil pressure, engine shaking and other abnormal phenomena. Therefore, these accompanying phenomena become the basis for assisting in the diagnosis of rattling faults.
