The Ironhead was a Harley-Davidson motorcycle engine, so named because of the composition of the rocker boxes. The engine is a two cylinder, two valves per cylinder, pushrod V-twin. It was produced from 1957 until 1985 and was replaced by the Evolution engine 1986.
This name may also be applied to the Harley-Davidson_Sportster motorcycles that used this engine.
The Ironhead Sportster engine was introduced in 1957 with the X Model Harley Davidson Sportster and lasted almost 30 years (THIRTY years !!!) until in 1986 this beautiful powerpack was replaced by the current Harley Evolution or Evo engine.
In 1986, Harley Davidson replaced the 1000cc Ironhead engine with the 1100cc Sportster Evolution or Evo engine. Because the smoother running Evo engine was developed with considerable help from outside the Motor Company, many people maintain that the Ironhead engine was the last real Harley engine.
The Ironhead version of Harley's Sportster has been around since 1957 and managed to survive until 1985, and, of course, the Evo version continues on today. All versions of the Sportster can trace their roots back to the VLs of the 30s. In fact the V begot the W, which begot the K, which begot the XL. And of course there are the racing sub-models, WRs, KRs and of course the ultimate XR. And a host of other sub-models, XLCs, XLCRs, XLCHs and XLHs. My favorite is the XLCH.The XL's direct predecessor, the K, took one of the main advantages of the side valve engine, the four cam design, and used that design to transition to the OHV XL. The four cam XLs have inherently better valve train geometry than any big twin engine Harley makes or has made. If fact, the twin-cam engine is an attempt to make up for some of that disadvantage. The second thing the K did was to eliminate a major flaw of all other Harleys, the separate engine and transmission cases. The unit construction of the K and XL is much sturdier, lighter and smaller than the big twin. It makes for lighter, better handling bikes. In fact the new big twins bolt the transmission directly to the engine, thus trying to gain back some of the advantage that the Ks and XLs have always had. And thirdly, the K had hydraulic suspension at both ends, which was passed on to the XL. I've owned and ridden rigid's with springer front ends; it is not what it is cracked up to be. Those bikes are ill handling, rough riding, kidney pounders. All in all, the XL is a better bike than the big twin. And the Ironhead is emblematic of everything that is raw and nasty about Harley. The XL Evo is a damn good motorcycle; it fixes the ills of the earlier XLs, but just doesn't capture the essence of the earlier XL. There is nothing like an old Ironhead for peeling the pavement off the road.