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Reasons of engine noises and solutions
The exceptional noise is often the auspice of a problem. If we can not find the reason and solve it timely, it will cause a big problem in the end and cause inconvenience, troubles and even unnecessary lost to you. Here, we introduce the characteristics of the exceptional noise of engine and methods to find out problems for your reference.
I. Exceptional noise on cylinder, piston and piston ring 
Noise caused by the impacting between piston head and cylinder cover
Noise characteristics:
The noise may occur on the part between the cylinder cover and cylinder when the engine moves in high speed. The mental sound continues all the time and often accompanies with the liberation of cylinder cover;
② Reasons of problem:
   a. The abrasion and move of crank bearing shaft and piston pin.Ii is often caused by the impact between piston head and valve cover when piston moves up and down;;
   b. The instinctive quality problem of product and the use of unmatched parts also may cause the impact between piston and valve cover when piston overtop the normal height;
   Remove the cylinder cover so as to inspect the insides or use proper parts and eligible products to change the damaged one. Adding a proper cylinder gasket is also a good way to prevent the impact.
II.Noise caused by impact between piston head and valve:
① Noise characteristics:
This problem only happens on the engine part where is near to the valve. At the joint between top of cylinder and cylinder cover, we can hear the cadent and fitful metal sound, which will become louder when the engine moves faster;
② Reasons of problem:
   a. The rocker changes and may cause the decrease of clearance in valve, which will make it touch the valve rod, when it librates at work. The result is the piston will touch the cylinder head in the process of exhausting or the adjusting gear will not match the mark;
   b. The unmatched size between valve rod and valve pipe will engender air-logged phenomena or make the materials overstep the expansion factor too much.
③ Solutions:
   a. First of all, judge which valve may impact on another.
Remove the valve cover;
Then touch or nip the rocker with a spanner and step the starting arm at the same time.
If our arm feels the shaking of the cracker axle, we can judge that this one is the bad one and adjust it to the standard timely
  b. Inspect the installing mark on timing chain wheel and flywheel;
 c. Otherwise, repair it and change the unmatched parts
III Noise on the piston ring
Mental sound on piston ring
   a. Break of ring and larger clearance between piston ring and its trough may cause the punching noise;
  b. When the cylinder head wears and tears, the clearance between cylinder and piston ring will hardly be rubbed to steps. Improper repair may cause the “pupu” sound when the cylinder and its steps impact on each other. It will become louder and louder with the acceleration of its running.
② Gas leak sound
   a. Causation and characteristics: lower elasticity of piston, larger clearance between pistons and troughs on inside cylinder all may cause the gas leak. It will engender a “chichi” noise “, even an obvious “pupu” noise. 
   b. Inspection method: put a little oil into the cylinder. If the noise decreases or disappears and then appears after a while, it indicates the gas leak.
③ Carbon accumulation caused noise
   a. Characteristics: it is a sharp noise, like “didi.”; and the engine is difficult to be ceased.
   b. Reason for carbon accumulation: the main reasons for it are the looseness between piston ring and cylinder, upside down installation of piston, superposition of piston hatches, the burning of oil in the firebox, the unqualified petrol and the dirty of air cleaner
IV Noises of valve
① Gas leak of valve: if there is a noise like “xuxu” on the part of exhaust mufflers, it means there is a gas leak on the engine valve. While, if there are noises everywhere on the air cleaner, it indicates that there is a leak on the engine inlet. The reasons for the leaks are:
a. The abrasion between valve and its washer, burning, flecks or hollow and carbon accumulation
b. Larger clearance between valve rod and pipe, shaking or bend of valve rod, deflection of valve head will cause the loose of valve;
c. The disjunction and decrease of spring elasticity also can cause the flab between valve and its washer;
d. Because the clearance in valve is too narrow, the rod and cracker will prop up the valve and cause a gas leak when the valve rod expands with heat;
Solutions: inspect the problem and repair or change the interrelated attrite parts according to actual condition.
② Characteristics: the cadent noise “ta ta” will increase with the acceleration of running and become disordered during the engine idling
Reason: improper adjustment of valve clearance
Solution: inspect or adjust the valve clearance after three to five minutes’ starting.
V. Knocking noise
Characteristics: This noise occurs at the beginning of the piston’s working. The piston swings around in the cylinder and hits the cylinder with its heads and middle part, which makes a harsh noise on the main part of cylinder. 
② Reasons:
   a. At the beginning of start, because of the enlarged space between piston and cylinder when piston contracts with cold, a light noise occurs and disappears gradually with the increase of piston’s temperature;
   b. At the beginning of the engine start, because the working condition is not good enough for lube to form oil film on the cylinder at lower pressure, the piston will hit the cylinder and cause the noise. After three or five minutes’ heating, the noise disappears with the natural work of lube;
   c. If the gas grade does not meet the requirement, the mixed gas will engender preignition and dieseling so as to make the hitting between the piston and cylinder;
   d. Such conditions all may engender the noise: driving on slope, driving in mud, and speeding up at high gear;
e. The piston’s abrasion may cause the column’s big error, which will cause the hitting between piston head and cylinder;
f. After long-time use, both piston and cylinder will be fayed and cause larger clearance between them, which could make the piston hit the cylinder when it swings in the cylinder at the very moment of start;
g. The bend of rod, the unmatched piston and piston hole and the unmatched con-rod bearing and crank pin also may engender the hitting.
③ Checking and analysis of problem
a. The “dang dang” noise is usually caused by the bad lubricated condition in the cylinder. Then we can add some lube and restart the engine to check the change of noise. If the noise disappears, it indicates that it is caused by the improper use of lube;
b. If there are “ta, ta ” noises and some blue smoke from the muffler, it usually indicates that the clearance between piston and cylinder is too large;
c. Because of the problem of production, the piston may does not match well with the cylinder so that there will be some noises when the piston moves irregularly.
④ Solutions:
   Any problem caused by a and b should be solved through warm-up of three to five minutes so as to let it form a film in the cylinder to reduce the parts’ abrasion; any problem caused by c should be solved through clearing the accumulated carbon and using the proper petrol while keeping the engine at normal temperature; any problem caused by f, g and h should be solved through dismantling cylinders, checking and repairing them separately.
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