S&S Cycle 3-Piece Flywheel - 4in. Stroke 320-0402 Vast improvement over stock flywheels which shift out of true under heavy load Heat treated 4140 material is 114% stronger than stock, eliminates thrust washer Larger 1.671in. crankpin, increased cross-sectional area for increased crank-pin clamping force. No welding required Integral mainshafts, truer flywheels and less vibration