Big Twin Evo models from 1990–up, which are factory equipped with the one-piece flywheel and pinion shaft, require this pinion shaft conversion kit in conjuntion with S&S Sidewinder or Stroker Kits, because S&S flywheels are using the earlier system with the pinion shaft bolted to the flywheel. The kit contains the pinion gear, oil pump drive gear, pinion shaft spacer and pinion shaft nut.