Excessive valve clearances will cause the duration of valve opening to

Excessive valve clearances lead to a longer time it takes for the valve to fully close after it has opened. This means that the valves will open later and close earlier than intended in their cycle, but primarily the key point is that they would not stay open longer than designed under increased clearance conditions.

By having greater clearance, the effective “duration” of the valve opening, which is the time during which the valve is actually open for the engine to allow intake or exhaust gases to flow, actually decreases over the engine cycle. Therefore, excessive clearance has the effect of shortening the effective time the valves remain open, thus leading to a decrease in the duration for both the intake and exhaust valves.

This ultimately affects engine performance, as a shorter duration of valve opening can lead to reduced air-fuel mixture intake and exhaust expulsion, impacting overall engine efficiency and operation.