Definition
A portion of a crankshaft that is displaced laterally from the main bearing centerline, providing the connection point for a connecting rod. The throw is the offset section formed by two crank cheeks and a crankpin, and its distance from the crankshaft's center of rotation determines the stroke of the piston.
Plain English
A part of the crankshaft that sticks out to the side of its main spinning axis. Each connecting rod attaches to one of these offset sections, and as the crankshaft turns, the offset pulls the piston down and pushes it back up.
Context Anchor
Seen in aircraft engine maintenance when studying crankshaft design, piston movement, and connecting rod attachment.
Derivation
Throw comes from the old mechanical sense of how far a moving part is 'thrown' from its center of rotation. In a crankshaft, the throw is literally how far the crankpin is offset from the centerline -- and that offset distance, multiplied by two, equals the piston's stroke.
Why Pilots Care
The throw distance sets the stroke, which directly affects engine displacement and power output. Technicians inspecting or measuring a crankshaft must understand throw geometry to evaluate wear, alignment, and balance.
Analogy
A bicycle pedal is attached away from the center of the crank. As it goes around, that off-center position creates useful motion, much like an offset throw does inside an engine.
Intuition Check
“Throw” does not mean tossing something here. It means the off-center reach of a crankshaft part. “Offset” does not mean accidental misalignment here. It is an intentional design feature.
Example Sentence 1
Each connecting rod attaches to its own offset throw on the crankshaft, so the pistons fire in the proper sequence as the shaft rotates.
Example Sentence 2
Mechanics checked the offset angles on each throw before reinstalling the crankshaft after overhaul.