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A brief history of the Harley-Davidson Evolution Engine

Harley DavidsonHarley Davidson has come along way since their first motorcycle prototype built in 1903

The Evolution (Evo) engine is a V-twin engine that has been manufactured by Harley-Davidson since 1984 for a variety of different motorcycle models. The engine design is often credited with saving Harley-Davidson from bankruptcy after the management buyout and subsequent reorganization that the company went through during the early 1980s. The name "evolution" was likely strategically chosen to coincide with a rebranding process that redefined Harley's image and helped regain its dwindling market share. Harley's Japanese competition had "evolved" and it was time to show their customers that they could, too.

Although the Evolution's engine design offered many advantages compared to previous Harley designs, the most important upgrades improved reliability and durability. After all, a large part of the company's downfall in the 70s had been due to outdated engine designs. The competition, particularly the Japanese companies, continued to innovate, creating motorcycles that lasted longer and cost lest to maintain than Harleys at the time. What little profit Harley-Davidson did manage to make at the time was wasted satisfying a growing number of warranty claims.

The newly designed Evo engine relied on aluminum heads and cylinders - as opposed to the heavy cast iron parts of the Shovelhead (their previous big bike V-Twin engine) and other predecessors, such as the Sportsters' Ironhead engine, led to a light weight engine with improved air-cooling efficiency. Since aluminum is a much better thermal conductor than iron, using aluminum also resulted in less wear and tear on head gasket seals and thus helped to make the engine much more durable than ever. The head gasket seals on the outdated Shovelhead engine were made of a combination of aluminum and cast iron, which caused unnecessary stress due to the different expansion rates and chemical properties of those two metals. This improved durability not only helped reestablish Harley-Davidson as an authority in the motorcycle industry, but also cut down significantly on their warranty costs.

EVO engine in the Sportster

In 1986, Harley-Davidson upgraded the Sportster with the newly designed Evo engine, replacing the Ironhead that had become a staple of the Sportster since its inception. Harley's decision to stick with the semi-unit construction of previous Sportsters resulted in a distinctly configured valve train. Unlike most of today's motorcycle engines, the Sportster Evo uses just one cam per each overhead valve, resulting in four independent gear driven camshafts. This setup results in cam lobes that are inline with each other, resulting in a parallel pushrod configuration. This design allows for VERY powerful cams.

A Harley Davidson Sportster with an 833cc Evolution Engine
Harley Evolution valvetrain with diagram: Purple indicates crank output, red indicates cams, yellow indicates pushrods, blue indicates rockers, dark green indicates valves, and light green indicates seats.

Since its inception in 1986, the Sportster Evo engine design has remained relatively untouched. Harley has updated other parts of the Sportster, most notably the transmission and motor mounts, resulting in some corresponding engine tweaks along the way. There are few differences in the construction of the 883 and 1200 cc Sportster Evo engines, the main one being a smaller bore on the 883 cc version. Because of the similarities, many people choose to upgrade their 883 Sporty with custom Harley parts to 1200 cc. Surprisingly, this can often be achieved at a much lower price than buying the factory 1200 cc version. Here is one option:

Sportster 833cc to 1200cc conversion kit

With this reasonably priced kit, you can upgrade your 833 Sporty to a 1200 with no head modification needed whatsoever. The pistons weigh exactly the same as your stock 883 pistons, eliminating the need for rebalancing your flywheels and absolutely no machining is necessary. Installation of this kit takes about the same amount of time as replacing the stock top end would, but you're guaranteed to have a bit more fun afterwards. Considering the factory 1200 cc Sporty costs over two grand more than its 833 cc counterpart, it's no surprise that many people buy the 833 and upgrade to the big bore head themselves.

It is hard to imagine a world without Harley-Davidson making motorcycles, but the truth is the company was very close to going bankrupt in the 1980s. After purchasing Harley-Davidson in 1969, American Machine and Foundry (AMF) had severely damaged the brand's image and reputation.

Decisions to cut the workforce and streamline production resulted in a lower quality product and disgruntled work force that eventually resulted in a labor strike. After 12 years of mismanagement, the company was sold back to a group of 13 investors (including Willie G. Davidson) for a mere 80 million dollars. They began designing the Evolution engine shortly afterwards, and the rest is history.


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