The Harley-Davidson VD was powered by the big twins Flathead used from 1929 to 1936 the displacement was 1930-1948 (1,200 ccm) and 1935-41 (1,300 ccm).
The classic Harley-Davidson engines are two-cylinder, V-twin engines with the pistons mounted in a 45° “V”. The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods.
This design causes the pistons to fire at uneven intervals, the consequence of an engineering tradeoff to create a large, powerful engine in a small space. This design choice is entirely vestigial from an engineering standpoint, but has been sustained because of the strong connection between the distinctive sound and the Harley-Davidson brand. This design, which is covered under several United States patents, gives the Harley-Davidson V-twin its unique choppy “potato-potato” sound.