1. The relationship between abnormal noise and engine speed
The existence of the most common abnormal noises in engines depends on the condition of the engine speed.
1. Abnormal noise only exists at idle or low speed. The reasons for the noise include: too much clearance between the piston and the cylinder wall; too tight mounting of the piston pin or too tight mounting of the connecting rod bearing too much clearance between the pusher and its valve guide hole; cam profile; sometimes the starter latch is loose and the pulley is damaged (squealing visible when changing speeds).
2. The sound is chaotic when maintaining a certain speed, and short-term sounds are emitted one after another during rapid deceleration. The reasons for the noise are: the camshaft timing gear is cracked or its fixing nut is loose; the crankshaft is cassé; the piston pin bushing is loose; The camshaft axial play is too large or its bushing is loose.
3. Abnormal noise occurs when the engine accelerates quickly, and the sound still exists when the engine runs at high speed. The reasons for the noise are: the connecting rod bearing is loose, the bushing is burned, or the size does not match and rotates; the crankshaft bearing is loose or the bushing is burned; broken.
2. The relationship between abnormal noise and load
Many abnormal noises on the motor are obviously linked to their load. When diagnosing, the load can be. cylinder removed by cylinder. The method is used to carry out the test, generally using the single or double cylinder ignition method to relieve the load on one or two cylinders to identify the relationship between abnormal noise and load.
1. The fire in a certain cylinder is cut offt the abnormal noise disappears or is reduced. The reasons for this noise are: knocking of the piston on the cylinder; loose connecting rod bearing; leaking broken piston pin;
2. If the fire in a certain cylinder is cut off, the sound will increase or there will be no sound at that time. The reasons for the noise are: the copper sleeve of the piston pin is loose; the conicity of the piston skirt is too great; the connecting rod bearing cover mounting bolts are too loose; or the connecting rod bearing is too loose; the alloy melted; The steering wheel mounting bolts are too loose.
3. The abnormal noise of two adjacent cylinders cutting the fire is reduced or disappears. The reasons for the noise are: a loose crankshaft bearing.
3. The relationship between abnormal sound and temperature
1. The sound is emitted at low temperature. When the temperature increases, the sound decreases or evene. disappears. The reasons for the noise are: the gap between the piston and the cylinder wall is too large; the piston is out of alignment due to the depth and width of the main bearing oil groove; engine oil pressure is low and lubrication is poor; .
2. There is a sound when the temperature increases, and the sound decreases or disappears when the temperature drops. Reasons for noise include: premature ignition caused by overheating; the long and short axes of the piston skirt ellipse are in opposite directions; the ovality of the piston is small and the gap between the piston and the cylinder wall is too small; is distorted; the gaps between the piston rings are too small.
4. The relationship between abnormal noise and motor duty cycle
Abnormal motor noise failures are often obviously related to motor duty cycle, in particular to abnormal operation of the crank. noises in the connecting rod mechanism and in the valve train are related to the work cycle. When it comes to four-stroke engines, any breakdown caused by the crank rod mechanism noise is caused by the engine running twice; All noises caused by the valve mechanism are caused by the engine running once.
1. The causes of abnormal noise caused by the crank-connecting rod mechanism are: the piston knocks against the cylinder wall; knocking noise from the piston pin; cylinder head ; the connecting rod. Bearings are too loose; Piston rings are leaking.
2. The causes of abnormal noise caused by the valve mechanism include: too much valve clearance; too much clearance between the tappet and guide hole and loss of cam profile; its guide clearance is too large; the springvalve rt is broken; the camshaft timing gear is broken radially; the valve seat ring is loose and cannot be closed;
3. If the abnormal sound has nothing to do with the work cycle, you should pay attention to the area where it makes the sound. Usually, the noise caused by the gap which has nothing to do with the duty cycle is mainly a fault in the engine accessories; If there is a continuous metallic friction noise coming from the machine parts that has nothing to do with the work cycle, this may indicate that some rotating parts are defective.
5. The relationship between abnormal noise and engine parts When abnormal noise occurs in the engine, a certain degree of vibration inevitably occurs. the characteristics and location of the vibration. This can help diagnose the cause of an abnormal noise.