Definition
The offset portion of a reciprocating engine crankshaft to which a connecting rod attaches. The throw consists of a crankpin (the journal that holds the connecting rod) joined to the main shaft by two cheeks. The distance from the centerline of the crankshaft to the centerline of the crankpin determines half of the piston stroke.
Plain English
The bent, offset part of a crankshaft that the connecting rod grips onto. As the crankshaft spins, this offset section swings around in a circle, which is what pulls the piston down and pushes it back up.
Context Anchor
Seen in aircraft engine construction, engine overhaul, and discussions of piston stroke and engine size.
Derivation
‘Throw’ here is the old mechanical sense of the word — the distance a moving part is ‘thrown’ away from its center of rotation. Same idea as the throw of a lever or switch: how far it moves off-center.
Why Pilots Care
Throw length determines piston stroke and engine displacement, directly affecting power output, balance, and the stresses the engine must withstand in flight.
Analogy
A bicycle pedal works in a similar way. The pedal is not in the center of the crank; it is offset, and that offset lets your foot make a circle and turn the gear.
Intuition Check
Do not read “throw” as something being thrown. In this engine term, “throw” means the amount of offset from the crankshaft’s center.
Example Sentence 1
Each crankshaft throw on the four-cylinder engine is offset 180 degrees from the next, so the pistons fire in the correct sequence.
Example Sentence 2
A six-cylinder engine has six separate throws spaced along the crankshaft to keep the power strokes evenly timed.