Here's why:
* Crankshaft throw: This is the distance from the center of the crankshaft to the center of the crankpin (the pin that connects the connecting rod to the crankshaft).
* Stroke: This is the total distance the piston travels from top dead center (TDC) to bottom dead center (BDC).
As the crankshaft rotates, the connecting rod moves the piston up and down. The piston travels the distance of the crankshaft throw on both the upstroke and the downstroke. Therefore, the total distance traveled (the stroke) is twice the crankshaft throw.
Example:
If a crankshaft has a throw of 3 inches, the stroke of the engine would be 6 inches (3 inches x 2 = 6 inches).
