Valve clearance refers to the gap between the valve and the rocker arm. If the valve foot gap is too large, the cylinder head position will have an obvious "tap" sound, and the car power drops, so the maintenance master will adjust the valve foot gap according to the abnormal sound.

Different teachers have different practical experience, which will draw different conclusions, and then affect their adjustment methods. For example, many people think that the valve gap is small hot car and large cold car, which will cause him to adjust the gap will be large and small, and some people will think that the gap will be large hot car and small cold car, and the gap will be small and large when adjusting.

Is it really that simple? In fact, due to the different material of the cylinder head and valve of the motorcycle, that is, the specific heat capacity and thermal expansion coefficient of the two are different, resulting in the change of the valve clearance with the time elapsed after the engine is started.

When starting the engine, because the specific heat capacity of the valve exposed to the combustion chamber is relatively low, and the volume is relatively small, that is, the temperature is relatively fast, so it is faster than the thermal expansion of the cylinder head, and the valve clearance is smaller.

When the engine is cooling, if the valve clearance is smaller than the specified value, it will cause the valve rocker arm to squeeze the valve so that it can not be completely closed, which may lead to poor compression and idle instability and other failures.

After starting, with the heating of the whole engine, because the coefficient of thermal expansion of the aluminum alloy cylinder head is larger than that of the steel valve, the once-small valve clearance will gradually become wider, and the valve clearance will be larger than that of the engine cooling.

If the valve clearance exceeds the allowable value when the engine is cooled, an abnormal "ticking" sound will occur after the cylinder head is fully heated.

Therefore, the valve clearance should be adjusted within a suitable range (see the technical parameters in the manual for details, it is best not to adjust arbitrarily by experience).

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