On which part of the cylinder walls of a normally operating engine will the greatest amount of wear occur?

On which part of the cylinder walls of a normally operating engine will the greatest amount of wear occur?

• A. Near the bottom of the cylinder
• B. Near the top of the cylinder
• C. Mid-stroke region
• D. On the cylinder head

Answer: (B)

Wear on the cylinder wall comes from the piston rings rubbing against the bore under load, with the amount of wear driven by the contact pressure and the lubrication film. The highest loading occurs near the top of the stroke, when combustion pressure is at its peak and the rings must seal against the bore as the piston nears top dead center. That elevated pressure pushes the rings harder against the wall and tends to squeeze oil film away, thinning the lubricant and increasing metal-to-metal contact. The temperature is also highest there, which can further reduce lubricant viscosity and worsen wear. The cylinder head isn’t the sliding surface in this context, and the bottom or mid-stroke regions see lower peak pressures, so they experience less wear than the top region.

Wear on the cylinder wall comes from the piston rings rubbing against the bore under load, with the amount of wear driven by the contact pressure and the lubrication film. The highest loading occurs near the top of the stroke, when combustion pressure is at its peak and the rings must seal against the bore as the piston nears top dead center. That elevated pressure pushes the rings harder against the wall and tends to squeeze oil film away, thinning the lubricant and increasing metal-to-metal contact. The temperature is also highest there, which can further reduce lubricant viscosity and worsen wear. The cylinder head isn’t the sliding surface in this context, and the bottom or mid-stroke regions see lower peak pressures, so they experience less wear than the top region.