The Difference Between A Knucklehead & An Ironhead

The Knucklehead and Ironhead are two V-twin engines produced by Harley-Davidson.

Harley-Davidson has produced many engines in its history. The Knucklehead and Ironhead engines were named after features of the engine and materials that were used to manufacture them. Both engines have markedly made their place in Harley history.


The Knucklehead is a 74-cubic-inch (1200 cc) engine that was distributed between 1936 and 1947. The Knucklehead has an overhead valve, V-twin design. The Knucklehead received its name due to its protruding rocker shaft bolts, which give the rocker boxes the look of a clenched fist.


Produced between the years of 1967 and 1984, the Ironhead Sportster is a 54-cubic-inch (883 cc) engine. It took its moniker from the fact that it was composed of an iron head and cylinders. The Ironhead has a reputation of being the meanest and loudest of the Harley V-twin engines.


In 1936, Harley introduced the Knucklehead Model E, which gained attention after the engine broke previous distance records. The last of the Knuckleheads was produced in 1947, leading the way to Harley’s Panhead engine. The Ironhead Model XL was introduced in 1957. The Ironhead Sportster was produced as a street model in 1958.