(Photos courtesy of Harley-Davidson)

1903 Single

In 1903, William S. Harley made a blueprint drawing of an engine designed to fit on a bicycle. The first Harley was built to be a racer and the single-cylinder engine had a 3-1/8 inch bore and a 3-1/2 inch stroke.

V-Twin 1909

Harley introduced its first V-Twin in 1909 and the configuration has been one of The Motor Company’s defining characteristics since. The engine had a displacement of 49.5 inches and produced seven horsepower with its two cylinders mounted at 45 degrees.


F-Head 1911 – 1929

In 1911, Harley-Davidson introduced the F-Head, an intake/inlet over exhaust-type engine. The OG Big Twin started as a 61 cubic-inch engine until the first 74 cubic-inch F-Head was introduced in 1922 on the JD and FD models. The F-Head was Harley’s workhorse until 1929.


Flathead 1929 -1973

The 45 cubic-inch Flathead was introduced on the 1929 D model. The side-valve equipped engine earned its name for its flat-topped, vented cylinder heads. A 74 cubic-inch version was introduced the next year in the V model. In 1937, the U series of Harley-Davidson Flathead Big Twins replaced the V series. Harley’s U and UL models were powered by 74 cubic-inch Flatheads while UH and ULH received a bigger 80 cubic-inch version. Variations of this engine can be found on Harley models as late as 1973.


Knucklehead 1936 – 1947

In 1936, Harley-Davidson introduced the EL with a 61 cubic-inch engine with overhead valves, Harley’s first production motorcycle with overhead valves. The engine had rocker boxes that looked like knuckles on a fist earning it the nickname Knucklehead. The engine had a circulating oil lubrication system that replaced the old “total-loss” oiling system boosting its efficiency. The Knucklehead was produced in 61 cubic-inch and 74 cubic-inch variations.


Panhead 1948 – 1965

In 1948, Harley-Davidson added aluminum heads and hydraulic valve lifters to the 61 ci. and 74 ci. overhead valve engines. They engines also received one-piece, chrome plated rocker covers shaped like cake pans, and thus the Panhead was born.

Ironhead Sportster 

Ironhead Sportster 1957 – 1985

Powered by a 55 cubic-inch overhead valve engine, Harley debuted the first Sportster in 1957. Who knew at the time that it would become the longest continually produced motorcycle in the Harley model line.

Sportster Evolution 1986 – up

In 1986, Sportsters began being outfitted with a variation of the Evolution engine with one cam per engine overhead valve. Initially the Sportster Evo was an 1100cc V-Twin until 1988. It currently powers Sportsters in either an 883cc or 1200cc version.


Shovelhead – 1966 – 1984

The first Shovelhead was introduced in 1966 on Harley’s Electra-Glide models. The Shovelhead was made in both 74 cubic-inch and 80 cubic-inch sizes and had a shallower combustion chamber, larger valve drop for both intake and exhaust, better porting, and stronger valves and pistons. Once again, the engine earned its nickname because of its rocker box covers which are slightly rounded and looked like an old coal shovel flipped upside-down, its pushrod tubes the shovel’s handles.

Evolution (80 cubic-inch)

Evolution – 1984 - 1999

Harley-Davidson unveiled its 1340cc Evolution engine in 1984 in five models, including the all-new Softail. The Evo produced more power, ran cooler, smoother and was oil-tight. Both the heads and cylinders are made from aluminum, cutting weight from the old cast iron design. The engine is believed to be a catalyst to the resurrection of the Harley-Davidson brand after the AMF years.

With the Evolution engine, Harley-Davidson had an engine that not only evolved from the Shovelhead, but was very different, and technically superior in a number of ways. The Harley Evo was not only more powerful, but it ran cooler and smoother than the Shovelhead. The 80 cubic-inch Evolution motor was produced between 1984 and 1999.

Twin Cam 88

Twin Cam 88 to Twin Cam 110  – 1999 – 2017

Twin Cam 88 - First introduced in Harley’s 1999 Touring and Dyna motorcycles, it was named for its two chain-driven cams. The 1450cc Twin Cam 88 had a reshaped combustion chamber, reworked exhaust and intake ports and valves which optimized emissions efficiency and power output, a single-fire ignition system, a cool-air intake from a new, bigger air cleaner, increasing both horsepower and torque over the Evo engine it replaced.

Twin Cam 96 – The 1584cc Twin Cam 96/96B engine and 6-speed Cruise Drive transmission debuted together on all Touring, Softail and Dyna models in 2007. The new engine, available only with Electronic Sequential Port Fuel Injection (ESPFI), featured a number of design enhancements aimed at making it more powerful, reliable and smoother. This included lighter pistons and lighter, shorter connecting rods, new, lighter cams, and a new crankcase design.


Milwaukee-Eight – 2017

Launched in 2017 in tourers and trikes, the Milwaukee-Eight (M8) was only the third all-new Big Twin Harley-Davidson had launched in 80 years. The M8 was released in three different versions, an air-cooled 107 cubic-inch model and liquid-cooled 107 cubic-inch 114 cubic-inch versions. The M8 differed from traditional Big Twins because it had four valves per cylinder, eight total, which gave the engine its name. Each cylinder has two spark plugs to increase the capacity of the intake and exhaust flow. The M8 also saw the return to a single-camshaft configuration used on previous Harley Big Twins from 1936 to 1999. All Milwaukee-Eights have internal counterbalancers whereas only Softails ran a counterbalanced Twin Cam.


Revolution Engine – 2001- 2017

The Revolution engine, introduced in the V-Rod models, was a drastic departure from the Harley norm. Built in collaboration with Porsche, the Revolution was a liquid-cooled, internally-balanced, 60-degree V-Twin with dual overhead cams. The Revolution featured offset cylinders and connecting rods mated to one-piece crankshafts. It was originally produced as a 1131cc (69 cubic-inch) powerplant until 2008 when it was bumped up to a 1247cc (76 cubic-inch) engine.

Revolution Max 

Revolution Max – 2021

Harley-Davidson’s Revolution Max is a liquid-cooled 60-degree V-Twin launched in both 975cc and 1250cc versions. It will power the new Pan America adventure-tourer and Bronx streetfighter. The 60-degree V-Twin features dual overhead cams, four-valve heads and dual down-draft throttle bodies. It has Harley’s latest electronic fuel injection system and new high-energy plug-top ignition coils. Two velocity stacks are housed in a massive air box. Though it is rubber-mounted to the frame, it has a single internal counterbalancer as well to keep vibrations to a minimum.