These cases are manufactured from 356-T6 and machined with state-of-the-art CNC equipment. This 4 to 5-speed case is designed for 4-speed Big Twin style frames with 1970-1984 Shovelhead style drivelines and chain final drives. These cases also accept most OEM and aftermarket 5-speed bearings, seals and other parts designed for 1985-1989 Big Twin style 5-speed transmissions. OEM trap door will require minor modification to fit this case. All modifications are thoroughly explained in the accompanied instructions. The Jims 4 to 5 speed transmission case is not compatible with the factory H-D primary belt drive as used on 1980-1983 FXSB Sturgis models. For applications that utilize an existing 4-speed drive line, a 1980 to early 1984 5-speed style chain-drive main shaft and 1980 to early 1984 style main drive gear must be used. These parts are compatible with the OEM tapered inner diameter clutch hub as used on 4-speed Big Twin. Basic case assemblies include the transmission case plus the shift lever adjustment screw, shifter shaft guide, and all studs and dowel pins required for assembly. To help insure a simple, trouble free installation, the studs and dowel pins are installed at Jims prior to shipment. The special, non-stock counter shaft bearing, inner primary bearing and mainshaft adapter spacer are not included, but must be ordered separately.