Definition
The inside diameter of a reciprocating engine cylinder, measured across the cylindrical surface where the piston travels up and down. It is one of the two key measurements (along with stroke) used to calculate an engine's displacement.
Plain English
The width of the hole inside an engine cylinder where the piston moves. A bigger bore means a wider cylinder.
Context Anchor
Seen in aircraft engine specifications, maintenance manuals, overhaul records, and discussions of piston engine size or wear.
Derivation
Bore comes from the Old English borian, meaning to drill or pierce. The cylinder bore is literally the bored-out hole inside the cylinder, machined to a precise diameter for the piston to fit and slide.
Why Pilots Care
Sets engine displacement and power output, directly affecting performance calculations and when an engine needs overhaul.
Intuition Check
Do not think of the bore as the piston itself. The bore is the inside width of the cylinder that the piston moves through.
Example Sentence 1
The mechanic measured the cylinder bore during overhaul to check for wear.
Example Sentence 2
During inspection the mechanic measured cylinder bore to check for wear.