What is the effect of excessive valve clearance in a piston engine?

Excessive valve clearance in a piston engine primarily leads to an increase in the amount of time that the valve remains open, which can actually reduce the effective valve overlap. Valve overlap refers to the period when both the intake and exhaust valves are open at the same time, facilitating better airflow and scavenging in the engine's combustion cycle.

When there is excessive clearance, the valves may not seat properly, leading to a decrease in the actual overlap since the timing of when these valves open and close can be altered. The intake valve may close later than intended, and the exhaust valve may open earlier, affecting the engine’s ability to breathe efficiently.

Moreover, negative impacts from excessive valve clearance often include increased engine noise and reduced engine efficiency due to poor combustion and timing issues. However, the focus for this question is specifically on the effect on valve overlap, linking to the timing adjustments that arise with excessive clearance.