Why are cam-ground pistons installed in some aircraft engines?

Cam-ground pistons are designed with a specific shape that deviates from a perfect circle when viewed from the end. This unique geometry allows the piston to fit more snugly within the cylinder at operating temperatures when expanded due to thermal effects. As the piston heats up, it changes shape slightly, and the cam ground design accommodates this change, promoting better alignment and reducing wear on the cylinder walls.

The improved fit enhances the overall efficiency of the engine by minimizing blow-by, which is the escape of combustion gases past the piston rings. Additionally, it helps maintain proper compression, leading to optimal engine performance and fuel efficiency.

While the other options present interesting ideas, they do not reflect the main purpose of cam-ground pistons. The compensating feature related to magnetos does not directly pertain to piston design, and equalizing wear on all pistons is more a result of uniform piston construction and operation rather than a specific design choice like cam-ground geometry. Thus, the primary reason for installing cam-ground pistons in aircraft engines is indeed to provide a better fit at operating temperatures.