Bore is defined as which of the following?

• A. The diameter of a cylinder
• B. The length of a piston stroke
• C. The thickness of a piston ring
• D. The width of a connecting rod

Answer: (A)

Bore is the diameter of the cylinder in which the piston moves. It’s the internal width measured across the cylinder bore. This dimension, together with the stroke (the distance the piston travels from top to bottom), determines the engine’s displacement, which is the total volume the cylinders move air and fuel through. The other options describe different measurements: the piston stroke is the distance the piston travels, the thickness of a piston ring is not the cylinder diameter, and the width of a connecting rod is unrelated to the cylinder bore.