Why didn't Neptune's motorcycle engine make abnormal noise before?

In general, check whether there is oil shortage first. If there is no shortage, it is likely that the valve clearance is large and the camshaft and rocker arm are worn. There are two solutions. Method one; Find a place to repair the motorcycle and adjust the valve clearance, if the effect is not ideal 2; Replace camshaft and rocker arm.

Another possibility is that the engine timing chain is loose, and this fault can only be replaced. The engine has abnormal noise. Maybe the maintenance can't keep up. Pay attention to change the air filter and oil on time, and change the gear oil. /kloc-change the oil once every 0/000 to 1500 km, an air cleaner twice, and gear oil once every 5,000 to 8,000 km. If there is, it is normal wear and tear. Just adjust or replace some wearing parts.