S&S Big Twin Generator style crankcases are designed to appear like stock original H-D cases Alternative to costly repairs when attempting to fix fatigued, broken, worn-out stock crankcases In spite of the stock appearance, these cases incorporate updated design features that improve overall engine strength and reliability S&S crankcases use Timken style sprocket shaft bearings 1956-99 Style and 1958 and later pinion bearings These cases will not accept stock 1957 and earlier flywheel assemblies Use 1936-69 Style oil pumps Machined for stock Panhead cylinder base oil feed Machined for the 1955-64 tin primary