An abnormal reduction in the diameter of the piston skirt due to heat or stress is known as what?

The term that describes an abnormal reduction in the diameter of the piston skirt due to heat or stress is known as piston collapse. This condition occurs when the molecular structure of the material of the piston skirt undergoes changes caused by extreme temperature or mechanical stress, leading to a decrease in diameter rather than the expected expansion that typically occurs when metal heats up.

Piston collapse can lead to engine performance issues, as the piston may not fit properly within the cylinder bore, potentially resulting in decreased compression and increased oil consumption. It's essential to monitor the health of an engine's components, especially in high-performance or heavily loaded conditions, to prevent such malfunctions.

The other terms, while related to piston behavior under varying conditions, do not specifically define an abnormal reduction in diameter. Piston expansion refers to the normal increase in size due to heat, piston contraction denotes a decrease in size as a part of normal thermal cycles, and piston fatigue relates to the material's weakening over time under repeated stress or cyclic loading, rather than an immediate reduction in size.