What is a consequence of excessive valve clearance on a cylinder in a reciprocating aircraft engine?

Excessive valve clearance in a reciprocating aircraft engine leads to a reduced valve overlap period. Valve overlap refers to the time when both the intake and exhaust valves are open simultaneously during the engine cycle. When the clearance at the valves is too great, the timing of valve events becomes altered, which can prevent the proper sequencing necessary for efficient engine operation.

This extended clearance can delay the closing of the intake valve and the opening of the exhaust valve, resulting in shorter periods where both valves are open. This can disrupt the scavenging process, which is crucial for ensuring that exhaust gases are effectively expelled and fresh air-fuel mixture is drawn into the cylinder. The optimal valve overlap allows for better performance, power output, and efficiency by utilizing the pressure waves created by the movement of exhaust gases.

Other choices, such as increased valve overlap period or improved engine efficiency, would be counterintuitive since excessive clearance generally leads to poor valve timing, which negatively impacts performance. The decreased weight of the valve isn't relevant to the consequences of inadequate clearance and doesn't directly pertain to the operational aspects of the engine's performance.