Harley Davidson Big-V-Twin Engine Lineup 1914 - Present

Have you ever wondered what the evolution and timeline of the Harley Davidson big V-Twin engine looked like since it was first introduced back in 1914?

Well you've come to the right place. I have collated numerous articles from around the internet into this one convenient location.

(Sources: Wikipedia, Harley-Davidson Museum, motorcyclistonline.com, along with various YouTube videos)

F-head, also known as JD, pocket valve and IOE (intake over exhaust), 1914–1929 (1000cc), and 1922–1929 (1200cc)

In a F-head/IOE engine, the intake manifold and its valves are located atop the cylinders, in the cylinder head, and are operated by rocker arms which reverse the motion of the push rods so that
the intake valves open downward into the combustion chamber. The exhaust manifold and its valves are located beside or as part of the cylinders, in the block. The exhaust valves are either roughly or exactly parallel with the pistons; their faces point upwards and they are not operated by separate push rods, but by contact with a camshaft through the tappet or valve lifter and an integrated valve stem/push rod. The valves were offset to one side, forming what seemed to be a pocket, leading to the term "pocket valve" being used for IOE engines. An F-head engine combines features from both overhead-valve and Flathead type engines, the inlet valve operating via push rod and rocker arm and opening downward like an overhead valve engine, while the exhaust valve is offset from the cylinder and opens upward via an integrated push rod/valve stem directly actuated by the camshaft, much like the valves in a Flathead engine.

Flat head, 1930–1949 (1,200cc) and 1935–1941 (1,300cc).

A flathead engine (a.k.a. sidevalve engine (SV), flathead, or flatty) is an internal combustion engine with valves placed in the engine block beside the piston, instead of in the cylinder head, as in an overhead valve engine. As the cylinder cross-section has the shape of an inverted L, other names such as L-block or L-head are also common.

The sidevalve's poppet valves are usually sited on one side of the cylinder(s). A recess in the cylinder head creates a corridor connecting the valves and the combustion chamber. The valve gear comprises a camshaft which operates the valves via simple tappets, most commonly without any further valvetrain components (such as push rods, rocker arms, overhead valves or overhead camshafts). Indian, however, employs both rocker arms and push rods to transmit motion from the cam lobes to the valve stems.

The sidevalve arrangement was once the most common across all motor industries (automotive, agricultural, marine, aviation, and others), but it has since fallen from favor in most multicylinder applications, such as automotive and aviation, having been displaced by overhead valve designs. Flathead designs are still commonly built new for many small engine applications of one and two cylinders, such as lawnmowers, rotary tillers, and two-wheel tractors.

Knuckle head, 1936–1947 61 cubic inch (1,000cc), and 1941–1947 74 cubic inch (1,200cc)

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, 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. As the design of Harley-Davidson engines has evolved through the years, the distinctive shape of the valve covers has allowed Harley enthusiasts to classify an engine simply by looking at the shape of the cover. The knucklehead engine valve covers have contours resembling knuckles on a person's fist that give the knucklehead its name.

Shovel head, 1966–1984, 74 cubic inch (1200cc) and 80 cubic inch (1338cc) since late 1978

The Shovel head engine is a motorcycle engine that was produced by Harley-Davidson from 1966 to 1984, built as a successor to the previous Pan head engine. When the engine was first produced, the Shovel head 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 “Shovel head” 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 Shovel head engine was created as the previous Pan head engine was becoming obsolete, with many Harley-Davidson owners demanding more power to compete with the more modern motorcycles. Throughout the Shovel head’s run, the engine had many different changes made to it to improve power, cooling and oil consumption. The engines had only 10 fins for cooling, which caused them to run hot. Another problem was that oil would pool in the cylinder heads, causing it to leak into the valves and burn oil.

Evolution (a.k.a. "Evo" and "Block head"), 1984–1999, 80 cubic inch (1340cc)

The Evolution engine (popularly known as Evo) is an air-cooled, 45-degree, V-twin engine manufactured from 1984 by Harley-Davidson for the company's motorcycles. It was made in the 1340cc (82 cu in) displacement for Harley-Davidson Big V-twins bikes, replacing the Shovel head engine until 2000 when the last EVO was placed in a production factory custom FXR4 (FXR2 and FXR3 were the first CVOs). In 1999, it was replaced by the Harley-Davidson Twin Cam 88 in the Touring and Dyna model and in 2000 in the Softail models. Also available in the Sportster model beginning in 1984, it was made in the 1,100 cc (67 cu in) displacement until 1988 and is still made in the 883cc (53.9 cu in) and 1200cc (73 cu in) displacements for the Harley-Davidson Sportster, replacing the iron head 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 attempt to reform its image following the 1981 management buyout from previous owner American Machine and Foundry.

Both the heads and cylinders of the Evolution engine are made from aluminum to reduce weight compared to a cast iron design. Air cooling efficiency is improved as aluminum is a superior thermal conductor to cast iron. The blocky rocker boxes (thus becoming nicknamed "block head" which never caught on), 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.

Twin Cam (a.k.a. "Fathead" as named by American Iron Magazine) 1999–present, in the following versions:
-Twin Cam 88, 1999–2006, 88 cubic inch (1450cc)
-Twin Cam 88B, counterbalanced version of the Twin Cam 88, 2000–2006, 88 cubic inch (1450cc)
-Twin Cam 95, since 2000, 95 cubic inch (1550cc) (engines for early C.V.O. models)
-Twin Cam 96, since 2007. As of 2012, only the Street Bob and Super Glide Custom Models still use   the 96.96 cubic inch (1584cc)
-Twin Cam 103, 2003–2006, 2009, 103 cubic inch (1690cc) (engines for C.V.O. models), 

The Harley-Davidson Twin Cam engines are motorcycle engines made by Harley-Davidson since 1998. Although these engines differed significantly from the Evolution engine, which in turn was derived from the series of single camshaft, overhead valve motors that were first released in 1936, they share a number of characteristics with nearly all previous Harley-Davidson engines. Both engines have two cylinders in a V-twin configuration at 45°, are air-cooled (some touring models use liquid cooling for the heads), and activate valves with push rods. The crankshafts have a single pin with a knife and fork arrangement for the connecting rods. These are sandwiched between a pair of flywheels.

The Twin Cam 88 was released for the 1999 model year in September 1998/ The Twin Cam 96 was released for the 2007 model year.

Milwaukee-Eight (a.k.a M8) 2017-Present
-Twin-cooled 107 ci (1750cc): Standard on touring and trike model year 2017+.
-Twin-cooled 114 ci (1870cc): Optional on touring and trike model year 2017+, standard on CVO models.

The Harley-Davidson Milwaukee-Eight engine is the ninth generation of "big twin" engines developed by the company, but only Harley's third all-new Big Twin in 80 years, first introduced in 2017. These engines differ from the traditional Harley Big Twin engines in that there are four valves per cylinder, totaling eight valves, hence the name. It also marked a return to the single-camshaft configuration as used on previous Harley Big Twin Engines from 1936 to 1999. In addition, the engines all have internal counterbalancers, whereas Twin Cams were counterbalanced only on Softail models, where the engine was rigidly mounted. 

Both engines have eight valves in two cylinders in the traditional V-twin configuration at 45°, are combination of air-cooled, liquid and oil-cooled, and activate valves with push rods. The 1746cc (107 cu in) model is standard on all touring and trike models, with the 1868cc (114 cu in) version remaining as an option, and standard on the CVO models.

Check out this great YouTube video showing the various Harley Davidson engines and how they would have sounded. It's unclear who created that awesome content but whoever you are bravo sir and thank you!

Tank

Vice President
Roughnecks MC
Toronto Chapter