What engine powered the original 1957 Harley-Davidson Sportster?

The original 1957 Harley-Davidson Sportster was powered by the Ironhead engine.

Ironhead was the common nickname for the Sportster’s overhead-valve V-twin because its cylinder heads were made from iron. The engine followed Harley-Davidson’s K-series design and gave the new Sportster a more performance-focused identity within the company’s range.

Ironhead is often mixed up with Harley-Davidson’s earlier Knucklehead and Panhead engines. Those names refer to different engine families, while Evolution was the later aluminum-head Sportster engine introduced in 1986.

The Ironhead engine remained associated with Sportsters for nearly three decades. Its long production run made it an important bridge between Harley-Davidson’s early overhead-valve V-twins and the more modern Evolution architecture.