When the motorcycle is riding for a long time, the engine will generally appear the phenomenon of too large or too small valve clearance, the motorcycle valve clearance is too large or too small, usually directly affect the performance of the car, we will adjust the valve clearance to the most appropriate state, can improve the engine performance, make the car more powerful, and also make the engine noise less. Many Mo friends do not understand the topic of valve, and do not know what the consequences of these problems will be. Here is a small series to give you an analysis.......

01 cylinder head structure

The cylinder head, cylinder block and piston of the engine comprise the combustion chamber, and the cylinder head is usually used with good cooling effect and high conductivity aluminum alloy due to its long-term high temperature and high pressure, because of its excellent thermal conductivity, which can ensure better cooling effect

02

Crankshaft and camshaft relationship

The timing sprocket is installed above the crankshaft, and the camshaft sprocket is installed on the camshaft of the cylinder head. The two sprockets are linked through the timing chain, and the number of teeth of the camshaft sprocket is twice the number of teeth of the timing sprocket.

Thus, in a four-stroke engine, the crankshaft rotates twice for the camshaft to rotate once. In this way, a working cycle of intake, compression, combustion and exhaust can be achieved.

03

Camshaft and valve rocker arm

The rotation of the crankshaft is transmitted to the camshaft through the timing chain, the camshaft rotation will produce thrust on the valve, so that the valve is opened or closed, each rocker arm is installed on the rocker arm shaft, the camshaft rotation, the rocker arm will be pushed up, so that it rotates around the rocker arm shaft, which will open and close the valve

The rocker arm is equipped with valve clearance adjustment screws, and the sliding surface of the camshaft must have sufficient lubricating oil to prevent wear, so the oil is crucial to the wear of the CAM

04

Valve phase

The crankshaft Angle corresponding to the actual opening and closing time and duration of the intake valve and exhaust valve is called the valve phase.

The valve phase diagram is the intake and exhaust valve opening and continuation period for optimal engine performance. As can be seen from the figure: only when the intake and exhaust valves are completely closed and the upper end of the intake and exhaust valves are not subject to the pressure of the rocker head, the upper end of the intake and exhaust valves may have a gap.

That is to say: not every time the piston runs to the top dead center, the inlet and exhaust valves are all closed, but to make full use of the inertia of the air flow, so that the cylinder can fully absorb fresh air and exhaust the combustion exhaust gas as far as possible.

05

Valve clearance

There is a gap between the end of the valve rod and the valve adjusting screw, which is called the valve gap. The gap is used as the gap for the valve and related components to expand under heat, so as to ensure that the valve is completely closed to seal the combustion chamber. When the engine is cooled, the valve gap must be adjusted to the specified range.

06

Variation range of valve clearance

When the engine is cold starting, the valve is heated faster and the expansion speed is faster than the cylinder head, making the valve clearance smaller than the engine is cold.

When the engine is heated as a whole, because the cylinder head is made of aluminum alloy material, the coefficient of thermal expansion is greater than that of the iron valve, and the valve clearance becomes larger from small to large. As the engine temperature continues to rise, the valve clearance becomes larger than that of the engine in cold state

If the valve clearance setting value is much less than the specified value when the engine is cold, the rocker arm will continue to press the valve, resulting in the valve can not be fully closed, resulting in air leakage and idle instability

07

Valve clearance adjustment

The valve clearance must be adjusted when the engine is cooling, and when the camshaft is not pushing the valve, when the piston is at the top dead center of the exhaust stroke, there is no clearance because the CAM is pushing the valve, so the valve clearance adjustment cannot be carried out. When adjusting the valve clearance, it is necessary to verify that the piston is at the top dead center of the compression stroke and that the T mark on the magneto rotor is aligned with the mark on the left cover

08

Valve clearance adjustment tool

What tools are needed for valve clearance adjustment?

It is recommended that you do your homework before starting, only after you are familiar with the engine maintenance manual, you can correctly perform the operation process, such as preparing the following tools and equipment

A common tool for disassembling motorcycles

feeler gauge

micrometer

Torque wrench

Protective gloves

Suction rod

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