Why do you need to repair ,even replace the valves frequently ?

Do you know why you need to adjust or repair ,even replace the valves after a certain amount of kilometers riding? It is owing to how the valves work!

It is very easy to explain how the valves work theoretically: the cam pushes the valves down into the cylinder against the spring,so gases can flow into the cylinder to assist in the completion of combustion and energy release,and then lets the valve shut under the force of the spring. The pressure in the combustion chamber rather neatly helps to open the exhaust valve,and than enter the next cycle.

As you can imagine what's the number of times this has to happen. Taking a bike engine revving at 10,000rpm as an example, each valve has to open and close 83 times per second, which means the valve has a lot of energy and is repeatedly slamming into the valve seat,meanwhile there's not much you can do about this.

That's why  you must adjust or repair ,even replace them frequently,A better way to extension their service life is to choose a stronger and lighter valves that can withstand all the slamming, and the combustion chamber's heat,you also should maintain your valves referring to the instructions.