The abnormal sound of the engine is a prelude to the engine's serious failure. In many cases, engine "noise" and "engine overheating" occur.
When the engine is working, abnormal noise is generated inside, mainly due to looseness, improper adjustment and poor maintenance quality of the parts that cooperate with each other. The abnormal noise inside the engine not only aggravates the wear of the related parts, but also causes serious damage to the engine.
Therefore, in the process of using the motorcycle, the sound of the engine should be carefully listened to, the abnormal noise inside the engine should be found, and the engine work should be stopped immediately. The professional should find out the cause and eliminate it.
Accurately determining the cause of abnormal noise inside the engine is difficult because there are certain similarities in the abnormal noise generated by faults of different natures on the same engine. On different engines, the abnormal noise generated by faults of the same nature is Different. In addition, when the engine is working, the normal sound will be mixed with the abnormal sound, not to mention the variety of vehicle engines. However, as long as the reasons for the abnormal noise of various different characteristics of the engine are fully understood, familiar with the various sounding parts, characteristics, timing and changing laws of different sounds, pay attention to the accumulation of experience, or accurately determine and determine the nature of abnormal sounds. , location and cause. This paper gives a brief introduction to the causes, characteristics, judgment and determination methods of common abnormal noise of the engine, for the readers and motorcycle enthusiasts to refer to.
1, the piston knocks the sound of the cylinder
1.1 The reason why the piston knocking sound is usually caused by the excessive clearance between the piston and the cylinder.
At the moment the engine is working, the piston is subjected to the pressure of the high pressure gas, oscillates in the cylinder and strikes the cylinder wall, producing an audible sound. In addition, when the piston is reversed ellipse, the connecting rod is bent or twisted, and the piston pin and the connecting rod copper sleeve (bearing) connecting rod big bearing are too tight, the piston is also knocked.
1.2 Piston knocking sound characteristics
a) When the engine is running at idle speed, the knocking sound is clear;
b) The knocking sound is obvious when the engine is cold, and the knocking sound is weakened or even disappeared after the temperature rises;
c) After the engine is broken, the knocking sound is weakened or even disappeared;
d) Inject a small amount (about 3mL) of engine lubricating oil into the cylinder from the spark plug hole, and slowly start the crankshaft to drive the crankshaft for about 1 minute to make the lubricating oil flow between the piston and the cylinder. When the engine is working, the knocking sound is weakened temporarily. Or disappear.
2, piston pin knocking sound
2.1 The cause of the piston pin knocking sound The reason why the piston pin knocking sound is usually: the piston pin and the connecting rod copper sleeve (the connecting rod bearing itself) or the piston pin seat hole are poorly matched. When the engine is working, the piston pin is up and down. Hit the connecting rod copper sleeve (bearing) or the piston pin seat hole to produce a knocking sound.
2.2 Piston pin knocking characteristics
a) When the engine is running at idle speed and medium speed, the “嗒嗒†knocking sound is clearer;
b) the frequency of the knocking sound increases as the engine speed increases;
c) After the engine temperature rises, the knocking sound does not weaken, and sometimes it is more obvious (this is a significant difference from the sound of the piston knocking cylinder);
d) When the fire breaks, the knocking sound will weaken or even disappear. At the moment of re-fire, there will be a clear 1 (å—’) or 2 consecutive (å—’å—’) knocking sounds;
e) When the test stick is in the upper part of the cylinder, the knocking sound is louder, and the tapping sound is smaller when the test stick is in the lower half of the cylinder;
f) The knocking sound is aggravated when the ignition time is slightly advanced.
3, the piston ring leaks sound
3.1 Piston ring leakage sound causes the piston ring leakage sound is usually caused by the fact that the piston ring and the cylinder wall are not sealed. At the moment when the engine works, the high-pressure gas enters the crankcase and makes a sound.
3.2 Piston ring air leakage sound characteristics of the piston ring leakage sound, similar to "knocking sound". For a four-stroke engine, the sound is reduced when the dipstick (with the oil cap) is removed.
4, the valve knocking sound
4.1 Causes of valve knocking The cause of valve knocking is usually: excessive valve clearance and cam wear, and the profile curve changes.
4.2 Valve knocking characteristics
a) The valve knocking sound is obvious and crisp, continuous and rhythmic. When the test is heard in the valve chamber, the knocking sound is obvious;
b) the frequency of the knocking sound changes as the engine speed changes;
c) the knocking sound does not change when the engine temperature changes and the fire is broken;
d) The knocking sound is weakened or disappeared when the engine rocker arm is held by hand or the feeler gauge is inserted during engine idle condition.
5, the connecting rod big head bearing sound
5.1 The sound of the connecting rod big head bearing caused by the sound of the connecting rod big head bearing is usually caused by: (using sliding bearing)
The connecting rod and the chain journal are poorly fitted, and the bearing (using the rolling bearing) is poorly worn. Due to poor lubrication, excessive bearing bushing, burnout, improper operation during repair or poor quality of the bearing bush, early wear and wear of the bearing balls (columns), when the engine works, they collide with each other to produce sound.
5.2 Sound characteristics of connecting rod big head bearing
a) When there is a sudden acceleration (from idle to medium speed), there is a clear continuous knocking sound (rolling bearing with abnormal noise inside the engine), which is the main feature of the sound of the connecting rod big head bearing;
b) When the big-head bearing of the connecting rod is worn (loose), the engine will have obvious sound when it is idle, and the sound will increase when the load is increased.
c) the sound does not change with the engine temperature;
d) When the engine is broken, the sound is obviously weakened or disappeared.
6, crankshaft bearing sound
6.1 Causes of crankshaft bearing sounds The causes of crankshaft bearing sounds are usually: (with the use of sliding bearings) the crankshaft journals and the crankshaft bushings are poorly coupled or bearing wear (using rolling bearings), at the moment of engine work, they collide with each other, producing sound .
6.2 Crankshaft bearing acoustic characteristics
a) When the speed is suddenly increased, there is a clear and heavy continuous knocking sound, and the engine is shaken;
b) there is no change in sound when the engine temperature changes;
c) When the fire is broken, the sound changes are not obvious;
d) When rolling bearings are used, the ball or roller retainer is damaged, the balls or rollers are rolled to one side, and each time the starter lever is stepped, there is a sound similar to the falling of the steel ball in the crankcase.
7, the piston ring knocking sound
7.1 Causes of piston ring knocking sound The piston ring knocking sound is usually caused by: the piston ring is broken; the piston ring is worn and loosened in the piston ring groove; the cylinder is seriously worn, and when the cylinder shoulder is formed, the piston is replaced after the piston ring is replaced. The ring collides with the cylinder shoulder; the piston pin opening locating pin of the two-stroke engine wears, so that the opening of the piston ring is displaced into the air port of the cylinder block.
7.2 Piston ring knocking characteristics
a) The piston ring knocks louder and dull;
b) the volume and frequency of the piston ring knocking sound rises and increases as the engine speed increases, and the sound is comminuted;
c) When the fire is broken, the volume is reduced but does not disappear. When the piston ring is broken, there is a “brushing†sound at the moment of re-fire.
8. Throttle knocking sound
8.1 Causes of Throttle Knocking Sounds The cause of the throttle knocking sound is usually that the carburetor's throttle and the mixing chamber have a serious wear surface. When the engine is working, the pulse of the combustible mixture acts to call the throttle. Under the poverty of the middle peasants to the wall.
8.2 Throttle knock characteristics
a) similar knocking sounds of the valve train mechanism;
b) the sound is not crisp;
c) When the engine is running at low speed and high speed, the knocking sound is not obvious or there is no knocking sound, and the knocking sound is most obvious when the throttle is at 1/4 opening;
d) Remove the connecting tube between the carburetor and the air filter so that the engine works at 1/4 of the throttle opening. When the finger is pressed against the throttle, the knocking sound disappears.
9, valve spring knocking sound
9.1 Causes of valve spring knocking The cause of valve spring knocking is usually: the valve spring is broken, and the broken valve springs collide with each other to produce sound when the engine is working.
9.2 Valve spring knocking characteristics
a) the metal knocking sound is continuous and messy;
b) the frequency of the knocking sound increases with the increase of the engine speed, but the volume changes are not obvious;
c) When the engine is broken, the knocking sound is almost unchanged;
d) After the top-mounted valve spring is broken, there is a “dangdang†sound of the piston top colliding with the valve, and the side-mounted valve spring has a “beep†sound after being broken.
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