* Thermal expansion. When your car is cold, the metal parts of the engine are contracted. As the engine warms up, the metal expands, which can cause the valves to tap against the valve seats.
* Low oil pressure. When your car is cold, the oil is thicker and doesn't flow as easily. This can cause the hydraulic lifters, which are responsible for keeping the valves in place, to not function properly, which can also lead to valve tapping.
* Worn or damaged valve lifters. If the valve lifters are worn or damaged, they may not be able to keep the valves in place properly, which can also lead to valve tapping.
Valve tapping is usually not a serious problem, but it can be annoying. If you're concerned about the valve tapping, you can take your car to a mechanic to have it checked out.
