Engine components — name and purpose of the piston's lower cylindrical portion In a reciprocating engine piston, what is the name of the lower cylindrical portion that helps guide the piston and aids heat dissipation to the cylinder wall?

Introduction / Context:
Accurate identification of piston features is important for assembly and diagnostics. The lower cylindrical section plays both mechanical and thermal roles.

Given Data / Assumptions:

• Conventional aluminium alloy piston with ring pack near the crown.
• Piston operates within a lubricated cylinder liner.
• Normal petrol or diesel engine architecture.

Concept / Approach:
The piston skirt is the lower cylindrical surface below the ring pack. It stabilizes the piston, controls side thrust, and provides area for heat transfer to the cylinder wall and then to the coolant. Proper clearance and lubrication at the skirt reduce scuffing and noise.

Step-by-Step Solution:

Verification / Alternative check:
Workshop manuals and piston drawings label the lower cylindrical region as the “skirt.”

Why Other Options Are Wrong:

• Crown: top surface exposed to combustion.
• Pin boss: localized bosses supporting the wrist pin.
• Connecting rod: separate component linking piston to crank.
• Oil control expander: part of ring assembly, not the piston body.

Common Pitfalls:
Misattributing ring-related oil control to the skirt; overlooking the need for proper piston-to-bore clearance.

Final Answer: