The main reason of motorcycle noise is too high.
1. Remove carbon deposit blockage
2. External cracking caused by corrosion or collision welding repair.
3. Internal silencing filter cotton crushed to death-recombination or lengthening?
4. Opening welding of internal partition-disassembly and repair welding
5. The connection between the exhaust pipe and the exhaust passage of the cylinder body is not tight-tighten the screw or replace the interface pad.
6. Abnormal combustion-check fuel, oil circuit or circuit.
7. The noise may be caused by the exhaust pipe problem. Look for cracks.
8. If the throttle is slow, check the carburetor and throttle cable.
9. The motorcycle vibrates a lot. If you refuel in neutral, it must be the engine. If it vibrates during driving, check whether the front and rear wheel bearings are aging and whether the fixing screws are loose.
Causes of Abnormal Noise of Motorcycle
Piston knocking sound
When the clearance between piston and cylinder is too large, the engine will produce a loud and sharp knocking sound when working, and it will produce a "click" sound when it suddenly accelerates or desensitizes. This kind of noise is most obvious when the engine is cold and accelerating, and it will decrease when the engine running temperature increases.
The inspection method is as follows
(1) Before the engine is started, you can't hear the knocking sound if you keep pedaling the starting lever. But when it starts, it suddenly accelerates and makes a "click" sound, which is the knocking sound.
(2) Remove the spark plug, inject about 1/20 liters of engine oil into the cylinder, press the starting lever several times, and then start the engine. If the noise is reduced or eliminated, it is caused by excessive clearance between piston and cylinder wall and temporary oil filling. But after a few minutes, the oil will become thinner, the oil will leak when heated, and the noise will still appear.
(3) With a long screwdriver (or metal bar), one end touches the upper part of the cylinder and the other end is close to the ear, and you will hear a "click" sound. Sometimes, due to the tight assembly of connecting rod small head cover and piston pin during repair, cylinder knocking will occur, but this kind of noise is dull and usually appears during automobile repair and start-up.
Knocking sound of piston pin
When the piston moves up and down, it will cause radial knocking and produce a crisp "click" sound. This kind of noise is generally obvious at high speed and rapid acceleration. Delay the ignition time, and the noise will be slightly reduced.
test method
Without starting the engine, if you keep stepping on the starting lever, you will hear the sound of "click, click" in the cylinder. After starting the engine, let the engine run at idle speed, touch the middle and upper part of the cylinder with a screwdriver, and listen with the ear side, with an obvious "click" sound.
Detonation sound caused by deflagration
When the engine suddenly accelerates or the motorcycle goes uphill, there is a continuous sharp "click" sound in the cylinder, which is the knocking sound caused by deflagration.
The knocking sound caused by deflagration is similar to the knocking sound caused by the excessive mating clearance between the piston pin and the connecting rod small head bushing. However, the knocking sound caused by deflagration will not occur at idle speed, and no sound can be heard when stepping on the starting lever before starting; After starting, the sound made by the piston pin is continuous and disorderly, and the knocking sound caused by deflagration is most obvious when the load is increased and uphill, and the sound is crisp.
The reasons for deflagration are as follows
(1) Use low octane gasoline;
(2) the ignition time is too early;
(3) the engine is overheated;
(4) Excessive carbon deposition in the combustion chamber;
(5) The spark plug has low calorific value.
Air leakage sound
If the fastening bolts between the cylinder and the cylinder head, between the cylinder and the crankcase or between the left and right crankcases are loose or the gasket is damaged, a "chirp" air leakage sound will be generated. After starting, the noise is not easy to hear when running at a constant speed; When stopping for inspection, obvious oil stains can be found from the air leakage. If this phenomenon is not serious, just tighten the fastening bolt; if it is serious, replace the gasket.
The knocking sound of the valve
If the valve clearance becomes larger due to improper adjustment or parts wear, the valve mechanism will make a short and sharp knocking sound. This kind of knocking does not change with the change of speed. It can be eliminated by adjusting the valve clearance or replacing worn parts.
Piston ring noise
If the piston ring is tortured, the elasticity of the piston ring is not enough, the piston is locked, or the clearance, side clearance and back clearance of the piston ring are too large, when the engine is running, explosive gas will rush down quickly and rush into the crankcase surface, making a knocking sound of air leakage. Touch the spark plug with a screwdriver and listen carefully. There is a clear "bang, bang" sound.
Sound of connecting rod big head bearing
Excessive wear of connecting rod big head bearing and bearing hole or excessive clearance during assembly will produce radial impact when crankshaft rotates and make a heavy "pop" sound. The noise is obvious when idling, and it is difficult to distinguish when running at medium and high speeds.
When checking, don't start the engine first, and press the starting lever continuously, and you will hear the sound of "click, click"; After starting, when idling, touch the lower end of the cylinder with a screwdriver and listen with your ears. There is an obvious "da da" sound.
Carburetor throttle knock
The throttle keeps moving up and down in the mixing chamber, and excessive wear leads to excessive clearance. In the intake stroke of the engine, due to the impact of airflow, the throttle swings radially and hits the mixing chamber, which will make a "giggle" sound. This noise is almost inaudible when idling, and the noise is the largest when the throttle is turned to 1/4. When the throttle is turned on again, the noise gradually decreases, and when the throttle is turned to the bottom, the noise disappears.
When checking, you can press the carburetor with a screwdriver to listen. When the accelerator is increased to 1/4, there is obvious knocking sound. You can also take off the air filter, put your finger against the throttle, the knocking disappears, and the relaxed finger knocking starts again, so you can conclude that it is the knocking of the throttle.
Carburetor backfire sound
Tempering sounds appear in two situations. One is that the air filter makes a "click" when starting, and white smoke comes out, making it difficult for the engine to start; The other is that the engine suddenly pops out of the air filter while working.
The reasons for backfire during carburetor start-up are as follows
(1) mixture is too thin;
(3) The spark of the spark plug is weak;
(4) The contact clearance of the circuit breaker is wrong;
(5) There is water in the oil;
(6) the oil circuit is blocked;
(7) The intake valve of the four-stroke engine is burnt out, and there is no gap between the intake valve and the tappet.
When the engine is working, the carburetor backfires suddenly, which may be caused by the following reasons:
(1) The engine was overloaded and failed to downshift in time;
(2) The capacitor is damaged or has poor contact;
(3) The oil circuit is blocked to make the mixture too thin;
(4) The intake valve of the four-stroke engine suddenly bites to death.
Exhaust pipe shooting sound
The sound taken by the exhaust pipe will also appear in two situations. One is that the combustible mixture burns and explodes in the exhaust pipe due to the poor working of the engine, which makes its sound crisp and loud, and at the same time emits sparks or smoke; The other is that due to the rupture of the muffler itself, a part of high-pressure waste gas is directly discharged into the atmosphere, making a "snapping" sound, which is weak, messy and uninterrupted.
In the former case, the reason for the exhaust pipe shooting is:
(1) mixture is too rich;
(2) The ignition time is too late;
(3) Deterioration or water content of gasoline;
(4) the capacitor is damaged;
(5) The exhaust valve of the four-stroke engine is stuck or the valve has no clearance.
Because the muffler exploded, it had to be welded again. If the opening at the back of the silencer is too big, you can also clamp the opening a little with pliers.