When a motorcycle is running, it often makes all kinds of noises. A motorcycle that works properly allows a certain amount of noise. But when a mechanism failure, cause abnormal sound, if not timely maintenance, it is easy to accelerate the wear and tear of the parts or damage, shorten the service life of the motorcycle. The following are some of the unusual sounds that usually occur.

1, piston cylinder knock: piston and cylinder clearance is too large, the engine work, will produce a large sharp tapping sound, sudden acceleration or reduce the feeling, "click" sound. The noise is most pronounced when the engine is cold and accelerating, and decreases when the engine is running at a higher temperature.

The inspection method is as follows:

(1) before starting the engine, continue to tap the starting lever, generally can not hear the tapping sound. But when the start, suddenly accelerated, it will occur "click" sound, that is to knock the sound of the cylinder.

(2) remove the spark plug, inject about 1/20 liter of oil into the cylinder, step on the starting lever several times, and then start the engine, such as noise reduction or elimination, is caused by the piston and cylinder wall gap is too large oil temporarily filled. But after a few minutes, the oil gets hot and thins out, and the noise still appears.

(3) with a long screwdriver (or a metal rod), one end of the contact with the upper part of the cylinder, the other end close to the ear, you will hear the "tap" tapping sound. Sometimes as a result of repair the connecting rod small head cover and piston pin, assembly is tight also can produce knock cylinder sound, but this kind of sound is more depressing, and generally is after the car starts to happen.

2, the tapping sound of piston pin: piston pin and connecting rod small head or piston pin and piston pin hole with too large clearance, piston up and down movement caused by radial percussion, produce a clearer "click" sound. This noise is usually apparent at high speeds and in sudden acceleration. Delay the ignition and the noise will be slightly reduced.

Check method: do not start the engine, continuously tap the starting lever, will hear a "click, click" sound in the cylinder. After starting the engine, make the engine idle, the screwdriver will touch the upper part of the cylinder, with the ear side to listen, there is a clear "click" sound.

3. Knock sound caused by deflagration: when the engine accelerates suddenly or the motorcycle goes up the hill, the cylinder gives out a continuous sharp "click" sound, which is the knock sound caused by deflagration.

The knock caused by deflagration is similar to that caused by the piston pin and the connecting rod small head bushing fitting clearance. However, the knock caused by deflagration will not occur at idle, and the starting lever can not hear the sound before starting; After starting, the noise of piston pin is continuous and disorderly, and the knock caused by deflagration is the most obvious when the load is increased and the hill is up, and the sound is clearer.

The causes of deflagration are :(1) the use of low octane gasoline; (2) premature ignition time; (3) overheating of the engine; (4) excessive carbon accumulation in the combustion chamber; (5) low calorific value of spark plug.

4, air leakage sound: between the cylinder and the cylinder head, the cylinder and the crankshaft box or crankshaft box, if the fastening bolts loose or gasket damage, will produce a "chirp" air leakage sound. After starting, the sound is not easy to hear when running at uniform speed; When stopped for inspection, visible traces of oil can be found from the leak. If this phenomenon is not serious, just tighten the fastening bolt can be, serious should be replaced gasket.

5, valve tapping: if due to improper adjustment or parts wear and tear valve clearance become large, valve mechanism will send short and sharp tapping. The tapping does not vary with the speed of rotation. Can be eliminated by adjusting valve clearance or replacing worn parts.

6, piston ring noise: if the piston ring torture, piston ring bullet is not enough, the piston ring around the lock or piston ring incision gap, side gap, back gap is too large, when the engine running, the explosion of gas will be rushed down, rushed into the crankcase surface air leakage knock. Touch spark plug with screwdriver, listen carefully, have clear "bang, bang" sound.

7, connecting rod big bearing sound: connecting rod big bearing and bearing hole excessive wear or assembly clearance is too large, crankshaft rotation will produce radial impact and a heavy "thud-thud" sound. Idle running sound is obvious, in the high - speed running noise is mixed and not easy to identify. During the inspection, do not start the engine first, continuously tap the starting lever, will hear the "click, click" sound; After starting, when idling, touch the lower end of the cylinder with the screwdriver and listen with the ears.

8, carburetor throttle knock: the throttle in the mixing chamber body is constantly moving up and down, due to excessive wear and tear caused by excessive clearance, in the engine intake stroke due to the impact of air flow, the throttle produced radial swing and hit the mixing chamber body, will emit a "cluck" sound. This sound in the idle when almost no sound, the throttle to 1/4 open the maximum sound, and then increase the throttle, the sound gradually reduced, when the throttle to the end, the sound disappeared.

When checking, can use screwdriver to hold carburetor to listen, in the throttle to 1/4 open, there is a clear tapping sound. Can also be removed from the air filter, with fingers against the throttle, the tapping sound disappeared, relax the finger tapping sound again, can be identified as the throttle tapping sound.

9, carburetor tempering sound: tempering sound occurs in two cases, one is the start, from the air filter out of the "crack" sound, and a white smoke, and the engine is difficult to start; The other is a sudden "snap" from the air filter when the engine is working.

10, exhaust pipe discharge sound: exhaust pipe discharge sound also occurs in two cases, one is due to the engine work is not good, so that the combustible mixture in the exhaust pipe combustion explosion and issued a "crackle" sound, sound crisp, loud, at the same time emit sparks or smoke; The other is due to the rupture of the muffler itself, so that part of the high-pressure exhaust gas directly into the atmosphere and produce a "crack" sound, the sound is weak, disorderly and uninterrupted. In the former case, the cause of discharge pipe blasting is :(1) the mixture is too thick; (2) ignition time is too late; (3) gasoline deterioration or moisture; (4) capacitor damage; (5) four stroke engine exhaust valve bite or valve clearance. As a result of the muffler break and release sound, generally can only be re - welding, if the muffler tail opening is too large, you can also use pliers to close the opening a little.