Evolution engine
Encyclopedia
The Evolution engine is an air-cooled, 45-degree, V-twin engine manufactured since 1984 by the Harley Davidson Motor Company
for the company's motorcycle
s. It was made in the 1340 cc displacement for Harley Davidson Big V-twins bikes, replacing the Shovelhead engine, until 1999 when it was replaced by the Harley Davidson Twin Cam 88s. It was made in the 1100 cc displacement and is still made in the 883 cc and 1200 cc (replacing the 1,100 in 1988) displacements since 1986 for the Harley-Davidson Sportster, where it replaced the ironhead Sportster engine.
Most analysts consider the Evolution to be the engine that saved the reorganized Harley-Davidson company from certain bankruptcy
. Harley-Davidson's official name for the engine was likely related to the company's reformed image following the Harley Davidson leadership_regained/1981 employee-led buyback from AMF.
Though a major design advance for Harley-Davidson in many ways, the Evolution is most distinct from earlier Harley-Davidson engine designs by virtue of its reliability, oil tightness, and ability to be run hard under all kinds of circumstances for tens of thousands of miles farther than any of its predecessors. Both the heads and cylinders of the Evolution engine are made from aluminum, which is both lighter than cast iron, reducing overall vehicle weight and a superior thermal conductor to cast iron - improving air cooling efficiency. A problem is avoided thereby which occurs when the heads and cylinders are of different materials. They expand and contract at different rates which induces a relative motion; this motion ruins the gasket seal and necessitates replacement. In water-cooled vehicles the oil and water will often mix and contribute to lubrication failure and engine destruction. The blocky rocker boxes
(thus becoming nicknamed "block head"), aluminum heads and cylinders (also referred to as "jugs") are the only part of the Evolution engine that can be said to be essential; the Big Twin and Sportster incarnations of the Evolution are significantly different.
The quasi-unit construction
of the Harley-Davidson Sportster, which has been part and parcel with the highly successful model line since its inception, was retained with the Evolution engine upgrade in 1986, resulting in a unique valve train configuration. Unlike almost any other engine in production today, the Sportster Evolution uses one cam per engine overhead valve
, resulting in four individual, single-lobe, gear-driven camshafts. The cam lobes are thus all located one behind another, and pushrods are arrayed in parallel fashion as a result. This allows each lifter and pushrod to deflect from the cam lobes perpendicular to the lobe plane. This configuration is friendly to radical, high-output cams, making the Sportster Evolution a natural choice for the once Harley Davidson owned line of Buell Motorcycle Company sportbikes from 1986 up to 2003.
The Sportster Evolution engine has remained largely unchanged from 1986 to 2006, though changes to the transmission, final drive and motor mounts have necessitated changes to the Sportster Evolution case. Construction is almost entirely the same between 883 cc and 1,200 cc versions; the chief difference between the two is a much smaller bore on the 883 cc, along with slightly different heads. Conversions from 883 cc to 1,200 cc are relatively inexpensive and commonplace, and cheaper than the price premium to go from a 883 to 1,200 engine on a new bike. Carburetors were standard on Sportster engines until 2007, when they were replaced by the Delphi Electonic Sequential-Port Fuel Injection
(ESPFI) system that had been optional since 2004.
The Big Twin utilizes a single, four-lobe, gear-driven camshaft
located just above the crankshaft
axis. While this simplifies camshaft replacement, it complicates the Big Twin valve train with tappet/lifters & pushrods that each deflect from the camshaft at wildly different angles. The Big Twin pushrods have a distinct helical appearance because the vertical plane formed by each cylinder's rockers (front-to-back) is exactly perpendicular to the vertical plane formed by the cam lobes (left-to-right). The need for one lifter & pushrod set to reach all the way out to the most outboard cam lobe gives rise to the Big Twin's tell-tale offset lifter assemblies, where the forward lifter assembly is located slightly farther out and rotated to enable the valve gear to make the reach.
The Big Twin has been accompanied by a number of different primary drives and transmissions, both on production Harley-Davidson motorcycles and in custom applications. The aftermarket selection of accessories for these closely related systems is wide, as it is for the engine itself.
The Evolution Big Twin motor is, for now, the last of the line of single cam, overhead valve motors tracing their lineage back to the ground breaking Knucklehead design penned by founder Bill Harley
. In its 1994 to 1998 final configuration, with rockerbox and base gasket leaks fixed, it proved to be a robust, durable, and versatile power plant for all of the Big Twin platforms. It is also the largest aftermarket supported Harley Davidson design, to date.
Harley-Davidson
Harley-Davidson , often abbreviated H-D or Harley, is an American motorcycle manufacturer. Founded in Milwaukee, Wisconsin, during the first decade of the 20th century, it was one of two major American motorcycle manufacturers to survive the Great Depression...
for the company's motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
s. It was made in the 1340 cc displacement for Harley Davidson Big V-twins bikes, replacing the Shovelhead engine, until 1999 when it was replaced by the Harley Davidson Twin Cam 88s. It was made in the 1100 cc displacement and is still made in the 883 cc and 1200 cc (replacing the 1,100 in 1988) displacements since 1986 for the Harley-Davidson Sportster, where it replaced the ironhead Sportster engine.
Most analysts consider the Evolution to be the engine that saved the reorganized Harley-Davidson company from certain bankruptcy
Bankruptcy
Bankruptcy is a legal status of an insolvent person or an organisation, that is, one that cannot repay the debts owed to creditors. In most jurisdictions bankruptcy is imposed by a court order, often initiated by the debtor....
. Harley-Davidson's official name for the engine was likely related to the company's reformed image following the Harley Davidson leadership_regained/1981 employee-led buyback from AMF.
Though a major design advance for Harley-Davidson in many ways, the Evolution is most distinct from earlier Harley-Davidson engine designs by virtue of its reliability, oil tightness, and ability to be run hard under all kinds of circumstances for tens of thousands of miles farther than any of its predecessors. Both the heads and cylinders of the Evolution engine are made from aluminum, which is both lighter than cast iron, reducing overall vehicle weight and a superior thermal conductor to cast iron - improving air cooling efficiency. A problem is avoided thereby which occurs when the heads and cylinders are of different materials. They expand and contract at different rates which induces a relative motion; this motion ruins the gasket seal and necessitates replacement. In water-cooled vehicles the oil and water will often mix and contribute to lubrication failure and engine destruction. The blocky rocker boxes
(thus becoming nicknamed "block head"), aluminum heads and cylinders (also referred to as "jugs") are the only part of the Evolution engine that can be said to be essential; the Big Twin and Sportster incarnations of the Evolution are significantly different.
Evolution on the Sportster
Unit construction
Unit construction is a term used to describe the design of larger motorcycles where the engine and gearbox components share a single casing. The term is sometimes applied to the design of automobile engines and was often loosely applied to motorcycles with rather different internal layouts such as...
of the Harley-Davidson Sportster, which has been part and parcel with the highly successful model line since its inception, was retained with the Evolution engine upgrade in 1986, resulting in a unique valve train configuration. Unlike almost any other engine in production today, the Sportster Evolution uses one cam per engine overhead valve
Overhead valve
An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block , and uses pushrods or rods to actuate rocker arms above the cylinder...
, resulting in four individual, single-lobe, gear-driven camshafts. The cam lobes are thus all located one behind another, and pushrods are arrayed in parallel fashion as a result. This allows each lifter and pushrod to deflect from the cam lobes perpendicular to the lobe plane. This configuration is friendly to radical, high-output cams, making the Sportster Evolution a natural choice for the once Harley Davidson owned line of Buell Motorcycle Company sportbikes from 1986 up to 2003.
The Sportster Evolution engine has remained largely unchanged from 1986 to 2006, though changes to the transmission, final drive and motor mounts have necessitated changes to the Sportster Evolution case. Construction is almost entirely the same between 883 cc and 1,200 cc versions; the chief difference between the two is a much smaller bore on the 883 cc, along with slightly different heads. Conversions from 883 cc to 1,200 cc are relatively inexpensive and commonplace, and cheaper than the price premium to go from a 883 to 1,200 engine on a new bike. Carburetors were standard on Sportster engines until 2007, when they were replaced by the Delphi Electonic Sequential-Port Fuel Injection
Fuel injection
Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....
(ESPFI) system that had been optional since 2004.
Evolution on the big bikes
The Evolution Big Twin (herein referred to simply as "Big Twin") saw a fifteen-year run in Harley-Davidson's "big bikes," in the Dyna, Softail, FXR, and Touring frames, and is basically a newer style top end and stroker flywheel assembly upon the slightly modified shovelhead case.The Big Twin utilizes a single, four-lobe, gear-driven camshaft
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
located just above the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
axis. While this simplifies camshaft replacement, it complicates the Big Twin valve train with tappet/lifters & pushrods that each deflect from the camshaft at wildly different angles. The Big Twin pushrods have a distinct helical appearance because the vertical plane formed by each cylinder's rockers (front-to-back) is exactly perpendicular to the vertical plane formed by the cam lobes (left-to-right). The need for one lifter & pushrod set to reach all the way out to the most outboard cam lobe gives rise to the Big Twin's tell-tale offset lifter assemblies, where the forward lifter assembly is located slightly farther out and rotated to enable the valve gear to make the reach.
The Big Twin has been accompanied by a number of different primary drives and transmissions, both on production Harley-Davidson motorcycles and in custom applications. The aftermarket selection of accessories for these closely related systems is wide, as it is for the engine itself.
The Evolution Big Twin motor is, for now, the last of the line of single cam, overhead valve motors tracing their lineage back to the ground breaking Knucklehead design penned by founder Bill Harley
William S. Harley
William Sylvester Harley was a co-founder of the Harley-Davidson Motor Company. He was born in Milwaukee, Wisconsin in 1880, and received a degree in Mechanical Engineering from the University of Wisconsin–Madison in 1907.He co-founded Harley-Davidson with Arthur Davidson in 1903 and served as...
. In its 1994 to 1998 final configuration, with rockerbox and base gasket leaks fixed, it proved to be a robust, durable, and versatile power plant for all of the Big Twin platforms. It is also the largest aftermarket supported Harley Davidson design, to date.