Which part of the piston experiences the most thermal expansion?

The correct answer is that the piston crown experiences the most thermal expansion.

In an engine, the piston crown is the top part of the piston that is directly exposed to the combustion process. As fuel combusts, it generates significant heat, causing the crown to reach higher temperatures than other parts of the piston. Consequently, the thermal expansion in this region is greater compared to other components like the piston pin, piston ring lands, and piston skirt.

The piston pin, which connects the piston to the connecting rod, does not experience the same level of direct heat exposure as the crown. Similarly, the piston ring lands, where the rings sit, and the piston skirt, which helps guide the piston in the cylinder, are also subjected to lower temperatures. Thus, the crown experiences the most thermal expansion due to its proximity to the combustion chamber and direct exposure to intense heat cycles, making it more susceptible to expansion compared to the other parts of the piston.