What is the piston crown?

• A. Upper part of a piston, directly responsible for changing the volume of a cylinder
• B. Lower part of a piston
• C. Side of a piston
• D. Piston pin

Answer: (A)

The piston crown is the upper surface of the piston that faces the combustion chamber. As the piston moves, this top surface directly contributes to changing the cylinder’s volume by sealing against the head and forming part of the combustion chamber ceiling. Its shape—flat, domed, or recessed—controls the compression ratio and how the air-fuel mixture burns, influencing both efficiency and power. The crown must withstand high temperatures and pressures, and its design helps manage heat transfer and flame propagation. The other parts mentioned refer to different areas of the piston: the lower portion is the skirt, the side is the piston’s lateral faces, and the piston pin is the fastener that attaches the piston to the connecting rod.