What does crankpin mean?
A crankpin is the offset pin on a crankshaft to which the connecting rod attaches at its large end. As the crankshaft rotates, the crankpin travels in a circular path while remaining fixed relative to the rod, and this arrangement converts rotary motion into reciprocating motion, or the reverse — as when pistons driving up and down in an engine turn the crankshaft and ultimately the wheels of a vehicle. The term belongs firmly to mechanical engineering vocabulary, appearing in discussions of internal combustion engines, steam locomotives, pumps, compressors, and bicycles. Engineers pay close attention to crankpin condition because it endures enormous alternating forces; wear or scoring of the pin or its bearing surfaces can lead to knocking, vibration, and eventual catastrophic engine failure. Though obscure to most everyday speakers, it names a component essential to nearly every machine that converts between spinning and back-and-forth movement.
nounThe offset pin projecting from a crankshaft, to which the big end of a connecting rod is attached, converting the shaft's rotation into reciprocating motion (or vice versa).
- The offset pin on a crankshaft to which the connecting rod's big end attaches.
"The mechanic discovered excessive wear on the crankpin after dismantling the engine."
"Wear on the crankpin caused the engine to knock under load."
"He polished each crankpin journal to a mirror finish before reassembling the motor."
Regular plural; typically used when discussing multi-cylinder engines, which have one crankpin per cylinder (or shared pins for paired cylinders).
"The V8's five main journals supported four crankpins."
Every time you pedal a bicycle or drive a car, you're putting your faith in one small steel pin doing all the work — the crankpin is where spinning becomes pushing.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of crankpin
The word crankpin is a straightforward compound of 'crank' — which entered English in the Middle Ages, likely via Old French from an earlier Germanic source — and 'pin', from Old English 'pinn', itself borrowed from Latin 'pinna' meaning feather or fin, later applied to pointed objects. The compound arose during the industrial era as engineers needed precise terminology for the parts of cranked shafts. It shares its first element with related terms such as crankshaft and crankcase.
How crankpin is actually used
Crankpin is a technical term confined chiefly to mechanical engineering and automotive contexts; it is rarely used outside discussions of engines, machinery, and crank-driven mechanisms.
Easily confused with crankpin
A crankshaft is the entire rotating shaft assembly, while the crankpin is just the offset pin on that shaft to which the connecting rod fastens.