These crankshaft assemblies for Evolution Big Twin are a direct replacement for 1984-1989 models and also work in 1990-1999 models when installed in conjuction with the pinion shaft gear parts as listed below. Contrary to the OEM crankshaft in 1990-1999 models these crankshafts feature a separate sprocket shaft and pinion shaft, which makes a rebuild possible. Another great advantage is that the 1984-1989 style pinion shafts have proven to be much stronger as the OEM design used in 1990-1999 models. Crankshafts are ready to install and balanced by S&S for use with stock pistons. Great for engine new builds and rebuilds.