market dynamics
What is the reason for the noise of the motorcycle? How does the motorcycle have unusual sound to return a responsibility?
Release date:2020.01.02

When a motorcycle is running, it often makes a lot of noise. The motorcycle works normally, allowing it to have a certain level of noise. But when a mechanism failure, cause abnormal sound, if not timely maintenance, it is easy to accelerate wear or damage parts, shorten the service life of the motorcycle.

The main reason for the sound of motorcycle is too loud

1. Carbon blockage -- removal

2. External cracking due to corrosion or collision -- welding repair

3. Internal silencing filter cotton is crushed to death -- restructured or lengthened

4. Open welding of internal partition -- disassembly and repair welding

5. The connection between the exhaust pipe and the exhaust duct of the cylinder block is not tight -- tighten the screw or replace the joint pad

6. Burning abnormally -- check fuel and oil lines or electricity

7. Loud noise may be a problem with the exhaust pipe, see if there is a crack.

8. Slow on the throttle, check the carburetor, pull the throttle.

9. The motorcycle has a big vibration. If the fuel is in neutral, the vibration must be the engine's problem. In case of vibration during driving, check whether the front and rear wheel bearings are aging and whether the fixing screws are loose.

The cause of abnormal sound caused by motorcycle

The piston struck the cylinder

Piston and cylinder clearance is too large, the engine work, will produce a larger sharp tapping sound, suddenly accelerate or reduce the feeling, the "click" sound. This noise is most obvious when the engine is cold and accelerating.

The inspection method is as follows

(1) before starting the engine, continuously step on the starting lever, generally can not hear the tapping sound. But when started, suddenly accelerated, it occurred "click" sound, that is, the sound of knocking cylinder.

(2) remove the spark plug, inject about 1/20 liter of oil into the cylinder, step on the starting rod several times, then start the engine, if the noise is reduced or eliminated, it is caused by the piston and cylinder wall gap is temporarily filled with oil. But after a few minutes, the oil gets hot dilute to leak, the sound will still appear.

(3) with a long screwdriver (or a metal rod), one end contacts the upper part of the cylinder, and the other end is pressed against the ear to detect the sound. Sometimes as a result of repair when connecting rod small head sleeve and piston pin, assembly is tighter also can produce knock cylinder sound, but this kind of sound is more depressing, and generally is after repair car start when just happening.

The tapping of the piston pin

Plug pin and connecting rod small head cover or piston pin and piston pin hole matching gap is too large, piston up and down movement causes radial percussion, producing a clearer "click" sound. This noise is usually more pronounced at high speeds and with sudden acceleration. Delay the ignition time, the noise will be slightly reduced.

Check the method

Do not start the engine, continuously step on the starting lever, you will hear a "click, click" sound in the cylinder. After starting the engine, make the engine run at idle speed. Contact the screwdriver with the upper part of the cylinder. Listen with your ears.

A knock caused by deflagration

When the engine suddenly accelerates or the motorcycle goes uphill, the cylinder gives out a continuous sharp "click" sound, which is the knock caused by deflation.

The knock sound caused by deflagration is similar to the sound caused by excessive clearance between piston pin and bushing of small head of connecting rod. However, the knocking sound caused by deflagration will not occur at idle, and the starting lever cannot be heard when stepping before starting. After starting, the piston pin sound is continuous and disorderly, and the knock sound caused by deflation is the most obvious when increasing the load and uphill, and the sound is more clear.

The causes of deflagration are

(1) low octane gasoline;

(2) premature ignition time;

(3) overheating of the engine;

(4) excessive accumulation of carbon in combustion chamber;

(5) low heat value of spark plug.


Between the cylinder and the cylinder head, between the cylinder and the crankshaft housing, or between the left and right crankshaft housing, if the fastening bolt is loose or the gasket is damaged, there will be a "chirp" leakage sound. After starting, the sound is not easy to hear clearly when running at a constant speed; When stopping for inspection, obvious oil stains can be found from the leak. If this phenomenon is not serious, just tighten the fastening bolt. If it is serious, the gasket should be replaced.

The tapping of the valves

If the valve clearance is enlarged due to improper adjustment or wear of parts, the valve mechanism will produce a short, sharp tapping sound. The tapping does not vary with the speed of the machine. It can be eliminated by adjusting valve clearance or replacing worn parts.

Piston ring noise

If piston ring torture, piston ring shell is insufficient, piston ring ring locked or piston ring cut clearance, side gap, back gap is too large, when the engine is running, the explosion of gas will be rapidly down, rushed into the crankcase surface to emit leakage knocking sound. Touch the spark plug with the screwdriver and listen for a clear "thump, thump" sound.

The rattle of the big-end bearing of the connecting rod

Excessive wear and bearing bore bearing bore or assembly clearance is too large, the crankshaft rotation will produce a radial impact and a heavier "dub dub" sound. The noise is obvious when idling speed running, while the noise is disorderly and hard to distinguish when running at medium and high speed.

When checking, do not start the engine first, continuously step the starting lever, will hear "clack, clack" sound; After starting, when idling, contact the lower end of the cylinder with the screwdriver and listen with ear.

Carburetor throttle tapping

The throttle valve is constantly moving up and down inside the mixing chamber, resulting in excessive clearance due to excessive wear. During the engine intake stroke, due to the impact of the airflow, the throttle produces a radial swing and hits the mixing chamber, which will send out a "cluck cough" sound. This sound is almost inaudible when idle speed is twirled, when the throttle is screwed to 1/4 opening degree, the sound is the biggest, when the throttle is increased again, the sound gradually decreases, when the throttle is screwed to the end, the sound disappears.

Check, can use screwdriver live carburetor audiometer, in the throttle up to 1/4 opening, there is a significant knock sound. The air filter can also be removed, with the finger against the throttle, the tapping sound disappeared, relax the finger tapping sound again, can be determined as the throttle tapping sound.

Carburetor tempering sound

Tempering occurs in two situations, one is to start, from the air filter issued a "crackle" sound, and out of a white smoke, and the engine is difficult to start; The other is when the engine suddenly makes a "popping" noise from the air filter.

There are several reasons for starting the carburetor tempering

(1) the mixture is too dilute;

(2) premature ignition time;

(3) weak spark of spark plug;

(4) the contact gap of the breaker is wrong;

(5) there is water in the oil;

(6) blocked oil line;

(7) the inlet valve of the four-stroke engine is burnt out, and there is no gap between the inlet valve and tappet.

When the engine is working, the carburetor is tempering suddenly, which may be caused by:

(1) the engine load is too heavy and the gear is not reduced in time;

(2) capacitor damage or poor contact;

(3) the mixture is too thin due to the blocked oil road;

(4) four-stroke engine intake valve suddenly bite dead, etc.

The exhaust pipe let off the cannon

The sound of the exhaust pipe discharging cannon also occurs in two cases, one is due to the engine work is not good, so that the mixture combustion explosion in the exhaust tube and issued a "crackle" sound, sound clear, loud, and emit sparks or smoke; The other is because the muffler itself is broken, so that part of the high-pressure exhaust gas directly into the atmosphere and issued a "crackle" sound, the sound is weak, messy and uninterrupted.

In the former case, the cause of discharge pipe firing is:

(1) excessive mixture;

(2) ignition time is too late;

(3) gasoline deterioration or moisture;

(4) capacitor damage;

(5) four-stroke engine exhaust valve bite dead or valve clearance.

Because the silencer is broken and produces discharge sound, can only re-weld, if the silencer tail opening is too big, also can use pliers will open the opening to clip a little.