Characteristics of abnormal noise in diesel engine

When diesel engine working in normal condition, the   engine sound will be smooth, rhythmic and coordinated. If the engine is   running, accompanied by other sound, such as the intermittent or continuous   metal percussion, continuous metal friction sound, etc., maybe the engine is   not working properly, this noise is called diesel engine noise. Diesel engine   noise is an important manifestation of engine failure, which is an important   basis for judging and analyzing the fault. Once abnormal sound shows, it   probably means the technical conditions of the engine body has changed.   Diesel engine noise has a certain regularity, if we can master the abnormal   sound characteristics of the diesel engine, it will be of great help for the   diesel engine troubleshooting .

1.Abnormal sound and diesel engine speed are closely  related

Most of the common diesel engine abnormal sound,  depends on the diesel engine speed status. Diesel engine speed change will  lead to the movement change of the moving engine parts, especially in the  rapid acceleration or rapid deceleration, the moving parts will have a  certain acceleration or deceleration, due to inertia. On the one hand may  lead to new engine differences, on the other hand, it will make the abnormal  sounds clear. Therefore, most common failure of diesel engine with abnormal  sound, largely depends on the diesel engine speed status.

In the analysis to determine the different engine   failure, it is appropriate to do a variety of speed tests to accurately find   abnormal sound cause of the malfunction.

(1) Give the engine a sudden increase in throttle, if   you can hear an obvious, clear abnormal sound, which could be a sign for   loose connection with main bearing or connecting rod bearing, or piston ring   friction.

(2) Run engines at a stable speed, if the abnormal   sound is disorder, and after give the engine a speed deceleration, the   abnormal sound becomes more obvious, this means problems such as the piston   pin bushing loose, camshaft axial clearance is too large ...etc.

(3) Run engine at idling or low speed, if the abnormal   sound is obvious, the problems may caused by the piston pin or connecting rod   bearing assembling too tightly, or a bad status of piston pin, valve and   valve tappet.

(4) Run engine at a middle speed, if there is an abnormal   sound, the problems could be the valve seat ring loosening, or camshaft   contour wear.

2. Abnormal sound and diesel load is closely related

 The force status of all engine moving parts, is   related to the changes in engine load, abnormal sound will change   accordingly. Some abnormal sound reducing with the load reduction; some   abnormal sound increasing with the load reduction; some abnormal noise sowing   with the load changes . The noise caused by the engine load is closely   related to diesel engine cylinder.

In the analysis and judgment of diesel engine abnormal   sounds, it will be appropriate to test the single-cylinder diesel engine by   taking a sudden load increasing and speed reducing, or suddenly  load   reducing and speed increasing; to multi-cylinder engines, we can test by   break the cylinder fire one by one or two adjacent cylinders to carry out   test and judgment.

(1) Increase single-cylinder diesel engine load, if the   abnormal sound getting loader relatively, the problem may caused by the   piston knocking cylinder, or the connecting rod and bearing ring noising;   with the engine load reducing, the noise generally occurs by valve seat ring,   or the noise of individual valve mechanism parts .

(2) For multi-cylinder diesel engine, if a cylinder off   the fire, and the abnormal sound relatively reduce or disappear, the problem   maybe caused by piston knocking cylinder, piston ring leakage or rod bearing   loosing; If the cylinder off fire and the abnormal sound showing up or   getting heavier, the problem may be piston sleeve sets loosing, connecting   rod bearing cover or flywheel bolts loosing ; if the adjacent two cylinder   off the fire and the abnormal sound getting lighter or disappeared, the   problem probably is main bearing loosing.

3. Abnormal sound is regular with the diesel engine   working cycle

(1) If the sound was caused by piston knocking, each   rotation of the crankshaft will cause a sound; and in a engine working cycle,   the crankshaft need to rotate twice, so if the abnormal sounds are caused by   crank link mechanism, in an engine cycle, it will sound twice. This sounds   could be caused by such as the piston pin percussion, rod bearing loosing and   piston ring leakage.

(2) When the engine works, the camshaft only turn one   time when the crankshaft turn twice, so if there is a sound caused by any gas   distribution mechanism, in each engine cycle, the abnormal sounds will only   ring once. Those sounds may be caused by such as, valve spring break, tappet   and its guide hole clearance is too large, cam profile wear, valve seat ring   release and camshaft timing gear radial rupture.

4. Abnormal sound is more sensitive to the temperature   of diesel engine

(1) If there is an abnormal sounds when the engine   temperature is at a low level, and the sounds reducing or even disappearing   when engine temperature increasing, the reason for above situation maybe   excessive clearance between the piston and the cylinder wall; piston    inaccurate due to the main bearing oil tank depth and width; oil pressure is   low and poor lubrication.

(2) If there is an abnormal sound showing after the   temperature rising, and the abnormal sound reducing or even disappearing when   the temperature decreasing, the reason for above situation could be engine   overheating preignition; the long and short axis of piston skirt oval in the   opposite direction; small piston ellipticity, small clearance between piston   and cylinder wall; piston deformation; small piston ring gap.

5. Abnormal sound is often accompanied by other diesel   engine failure phenomenon

Once the diesel engine abnormal sound showing, often   lead to other diesel engine failure. Such as oil pressure drop, poor   lubrication; speed instability, engine jitter; poor start, power shortage;   fuel consumption increasing, smoke color anomalies. These fault phenomena   contribute to the accurate analysis, judgment and elimination of abnormal   sound, such as connecting rod bearings loosing too much, the inlet and   exhaust valve stuck, large clearance between piston and cylinder wall, all   these situation can not only produce abnormal sound, but also will lead to   oil pressure drop, or causing the individual cylinder does not work,   pulsating smoke phenomenon.