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