Harley-Davidson Knucklehead V-Twin Motorcycles – HISTORY OF THE BIG TWIN The H-D Knucklehead V-twin was introduced in 1936. Here’s a look at the technical evolution of the 61-cu.-in. engine and chassis of Harley-Davidson’s first OHV Big Twin. The H-D Knucklehead V-twin was introduced in 1936. Here’s a look at the technical evolution of the 61-cu.-in….