Crankcase

External housing for the crankshaft.

Vertically split

Vertical crankcases are crankcases that are split vertically.

Horizontally split

The crankcase has a seam on the horizontal plane. Horizontally split crankcases were a major innovation when they were first introduced. They caused the bikes that featured them to be FAR less prone to oil leaks.

Cassette type

The gears are loaded in from one side.