market dynamics
Motorcycle engine valve clearance, why some will become larger, and some will become smaller?
Release date:2020.03.25

       Engine valve mechanism directly determines the performance of the engine, and the valve in the whole valve mechanism is a crucial component, so when the valve gap changes, the performance of the engine will be deviated.


       The so-called valve gap is the gap between the top of the valve stem and the rocker arm. This gap is to ensure that the valve can be tightly closed without leakage. It is necessary for a four-stroke internal combustion engine, but if the gap exceeds the specified value, it is abnormal.

       The most important factor for changing the valve clearance is the engine temperature and normal wear, the temperature of the engine increases with the length of the engine running, and the normal wear increases with the length of the engine's life, so the valve clearance changes.

       According to actual use conditions, the engine valve clearance will be smaller, and the exhaust valve clearance get bigger, the main cause of the difference, lies in the inlet valve inlet pressure will be larger, so it will be greater than the exhaust valve wear degree, and this is why adjust valve clearance, inlet valve will be slightly bigger than the main basis of the exhaust valve.

       The main reason for the increased exhaust valve clearance is the normal wear and tear of the rocker arm and camshaft. As a high speed rotating part, the wear of the camshaft is normal. Once it is worn, there will be too much clearance between the rocker arm and valve.

The above is the main reason for valve clearance to become larger or smaller, then why is the same wear caused by the change in valve clearance, the intake valve will become smaller and the exhaust valve will become larger?

      The secret here is that the main part of the wear is not the same, the main wear part of the intake valve, in the valve working part is in the valve work surface, and the impact of the exhaust valve clearance changes in the wear, mainly on the camshaft, such a difference will make the parts of the displacement direction will be slightly different.

       After the valve working face is worn, it will move slightly towards the cylinder head (up), while after the rocker arm is worn, it will move towards the cylinder body (down), so that it will appear that the valve clearance changes under the same wear condition, and the final clearance size will be different.