Which component is NOT part of the piston?

The piston of an engine is a crucial component that interacts with various parts of the engine to facilitate the internal combustion (or other types of) cycle. To understand why the selected answer is not part of the piston, it's important to look at the function of each part commonly associated with a piston.

The piston skirt, for instance, serves as a guiding surface, allowing the piston to move smoothly within the cylinder while maintaining a proper clearance. The piston lands are the top rings of the piston that provide a seal against the cylinder walls to prevent combustion gases from escaping and to ensure efficient engine operation. The piston stem similarly refers to a part that would typically contribute to the piston’s height and function within the cylinder.

In contrast, the term "piston journal" typically refers to a part of the crankshaft or connecting rod assembly rather than the piston itself. It is related to the axis around which the connecting rod pivots, rather than being an integral component of the piston structure. Therefore, identifying the piston journal as not being a part of the piston emphasizes the distinction between the components and their specific roles within the engine assembly. Understanding these components helps clarify the relationships and functions within an engine, which is vital for anyone studying or working in small engines.