The Norton Commando is a British Norton-Villiers motorcycle with an OHV pre-unit parallel-twin engine, produced by the Norton Motorcycle company from 1967 until 1977. Initially having a nominal 750 cc displacement, actually 745 cc (45.5 cu in), in 1973 it became an 850 cc, actually 828 cc (50.5 cu in). It had a hemi-type head, similar to all OHV Norton engines since the early 1920s.

A straight-twin engine, also known as an inline-twin, vertical-twin, or parallel-twin, is a two-cylinder piston engine whose cylinders are arranged in a line along a common crankshaft.