Question: Which ANA motorcycle engine is named after a dragon in Norse mythology?
Context: In Norse mythology, Fáfnir (Old Norse and Icelandic) or Frænir is a son of the dwarf king Hreidmar and brother of Regin, Ótr, Lyngheiðr and Lofnheiðr.  After being affected by the curse of Andvari's ring and gold, Fafnir became a dragon and was slain by Sigurd. In Norse mythology, Gná is a goddess who runs errands in other worlds for the goddess Frigg and rides the flying, sea-treading horse Hófvarpnir (Old Norse "he who throws his hoofs about", "hoof-thrower" or "hoof kicker").  Gná and Hófvarpnir are attested in the "Prose Edda", written in the 13th century by Snorri Sturluson.  Scholarly theories have been proposed about Gná as a "goddess of fullness" and as potentially cognate to Fama from Roman mythology.  Hófvarpnir and the eight-legged steed Sleipnir have been cited examples of transcendent horses in Norse mythology. The knucklehead is a retronym used by enthusiasts to refer to a Harley-Davidson motorcycle engine, so named because of the distinct shape of the rocker boxes.  The engine is a two-cylinder, 45 degree, pushrod actuated overhead valve V-twin engine with two valves per cylinder.  It was the third basic type of V-Twin engine used by Harley-Davidson, replacing the Flathead-engined VL model in 1936 as HD's top-of-the-line model.  The engine was manufactured until 1947 and was replaced by the Panhead engine in 1948.  The Knucklehead-engined models were originally referred to as "OHVs" by enthusiasts of the time and in Harley's official literature; the nickname arose from the California chopper culture of the late 1960s. In Norse mythology, Mjölnir (Old Norse: "Mjǫllnir" , ] ) is the hammer of Thor, a major Norse god associated with thunder.  Mjölnir is depicted in Norse mythology as one of the most fearsome and powerful weapons in existence, capable of leveling mountains.  In his account of Norse mythology, Snorri Sturluson relates how the hammer was made by the dwarven brothers Eitri and Brokkr, and how its characteristically short handle was due to a mishap during its manufacture.  Similar hammers (Ukonvasara) were a common symbol of the god of thunder in other North European mythologies. Elizabeth Hall Boyer (born 1952) is an American fantasy author who produced a number of books in the 1980s and early 1990s.  Her stories were deeply influenced by Norse mythology, and are set in a fantasy world whose climate and geography resembles that of the Scandinavia of Norse myths.  While Norse mythology has been an influence on the fantasy genre, and many authors such as Tolkien and Lewis were influenced by these myths, Boyer's books followed them much more closely.  Her stories are characterized by light and dark elves, dwarves, trolls, sorcerers, ley lines, burial mounds, wizards, and so forth.  Boyer tended to follow the Norse versions of these story elements closely without much deviation.  Boyer's early books are dominated by the theme of the heroic quest. The Norse mythology, preserved in such ancient Icelandic texts as the Poetic Edda, the Prose Edda, and other lays and sagas, was little known outside Scandinavia until the 19th century.  With the widespread publication of Norse myths and legends at this time, references to the Norse gods and heroes spread into European literary culture, especially in Scandinavia, Germany, and Britain.  In the later 20th century, references to Norse mythology became common in science fiction and fantasy literature, role-playing games, and eventually other cultural products such as Japanese animation. The Shovelhead engine is a motorcycle engine that was produced by Harley-Davidson from 1966 to 1984, built as a successor to the previous Panhead engine.  When the engine was first produced, the Shovelhead had a shallower combustion chamber, larger valve drop for both intake and exhaust, better porting, and stronger valves and pistons.  This gave the new engine an extra 10 horsepower, along with a different appearance.  The engine gained the nickname “Shovelhead” due to the look of the rocker heads having the appearance of an old coal shovel that was flipped upside down, giving the appearance of a shovel.  While the engine did have problems earlier in its timeline, the new and improved motor gave Harley-Davidson a 26% sales increase. The ANA motorcycle was manufactured by Martin J Shelley at the ANA Cycle Works in Rathdowne Street, North Carlton, Victoria between 1910 and 1919.  The ANA used a wide variety of different engines: Fafnir, JAP Precision, Abingdon King Dick, as well as Sturmey-Archer gearboxes. A big bang engine is an unconventional motorcycle engine designed so that most of the power strokes occur simultaneously or in close succession.  This is achieved by changing the ignition timing, changing or re-timing the camshaft, and sometimes in combination with a change in crankpin angle.  The goal is to change the power delivery characteristics of the engine.  A regular firing multi-cylinder engine fires at approximately even intervals, giving a smooth-running engine.  Because of a big bang engine's power delivery imbalance, there exists more vibration and stress in the engine.  Thus, the power peaks are very strong and can overwhelm the rear tire (if used in a motorcycle), but when the rear tire does slide, the temporary lull in power between power strokes generally makes the slide easier to catch. Norse mythology is the body of mythology of the North Germanic people stemming from Norse paganism and continuing after the Christianization of Scandinavia and into the Scandinavian folklore of the modern period.  The northernmost extension of Germanic mythology, Norse mythology consists of tales of various deities, beings, and heroes derived from numerous sources from both before and after the pagan period, including medieval manuscripts, archaeological representations, and folk tradition.
Answer: Fafnir became a dragon