When Harley-Davidson riders talk about their bikes, the conversation rarely stops at model names and years. Before long, names such as Knucklehead, Panhead, Shovelhead, Evo, Twin Cam and M8 come into it too.
For someone new to Harley, these might sound like nicknames passed around among friends. For riders who have lived with the bikes for years, an engine name can bring an entire era into focus: how the motorcycle looks, what it takes to maintain it, and how its owner might choose to customise it.
That makes the engine a good place to begin getting to know Harley-Davidson. Follow its powerplants through the years and you will find both the continuity of the traditional V-twin and the experiments that have developed alongside it.
In this first episode of The History, we trace the story from the single-cylinder engine of 1903 to the engines of the present day. Big Twin provides the main thread, with Sportster, the small motorcycles of the Aermacchi era and the liquid-cooled families filling out the picture before we explore each story in later episodes.
Explore by era
Different routes, one timeline
New engines did not replace every older family at once. This timeline separates six important threads, making their overlapping eras easier to see.
Six groups to guide the story
This map organises the article. It does not imply that every engine within a group directly inherits its design from the others.
Big Twin
F-head → Flathead V/U → Knucklehead → Panhead → Shovelhead → Evolution → Twin Cam → M8
The main thread of Harley’s large road motorcycles.Sportster
Model K/KH → Ironhead → Evolution Sportster
Revolution Max also powers newer Sportster models, but uses a different engine architecture.45 & Other Twins
Flathead 45 · WL/WLA/WLC · Sport Twin · XA
The 45 is a V-twin; Sport Twin and XA use horizontally opposed cylinders.Singles & Small Bikes
Early singles · A/B · Small two-strokes · Topper · Aermacchi · X440
Small motorcycles from different production sources, with different engine layouts.Modern Engines
Revolution · Revolution X · Revolution Max · X350/X500
Liquid-cooled V-twins are distinguished from parallel twins.Racing
Eight-Valve · Two-Cam racer · WR/KR · XR750 · VR1000 · XG750R
Competition engines developing alongside the road-bike families.1903 — A beginning with just one cylinder
The familiar image of a Harley-Davidson is a pair of cylinders arranged in a V at the centre of the frame. The company’s earliest motorcycles, however, were powered by a single cylinder.
In 1903, William S. Harley, Arthur Davidson and their fellow founders were working towards something beyond a small engine attached to a bicycle. They developed an engine and frame designed to work together as a motorcycle. These were the beginnings of what became Harley-Davidson.
The early F-head single continued to develop and remained in the range through the 1918 model year. It is a reminder that, before Harley became famous for its V-twins, the company had built its identity around simple motorcycles producing just a few horsepower. 1, 2
An early single-cylinder engine representing the 1903–1918 family; the exhibit does not establish that this particular engine dates from 1903.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01909–1929 — Two cylinders take the shape of a V
In 1909, Harley-Davidson offered its first production V-twin, with the cylinders set at an angle of 45 degrees. That layout would become a defining feature of the company’s traditional engines.
The first version had reliability limitations and was sold for only one year. An improved F-head V-twin followed in 1911 and remained in the range through 1929.
For this article, that period forms the foundation of the Big Twin story familiar to riders today. The V layout was already established, but another engine group stood between those early engines and the Knucklehead: the Flathead. 1
Harley also built the Sport Twin, or Model W, from 1919 to 1923. Its horizontally opposed cylinders represented a different architecture from the V-twin. Despite the suggestive name, it was not a Sportster. This Model W must also be distinguished from the later W-series motorcycles powered by the 45-cubic-inch engine. 15
The improved F-head V-twin introduced in 1911.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A 1909 Model 5-D displayed alongside a 1906 single-cylinder motorcycle.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Sport Twin / Model W, 1919–1923: a separate branch from Sportster.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01929–1948 — Flathead, before the familiar rocker-cover nicknames
The Flathead name comes from the relatively flat shape of its cylinder heads. Its valves sit beside the cylinders in a side-valve arrangement, giving it a very different appearance from engines with rocker assemblies above the heads.
Harley introduced a 45-cubic-inch Flathead V-twin in 1929. The larger 74-cubic-inch V-series followed for the 1930 model year, with the U-series taking over in 1937.
For Flathead Big Twins specifically, the main period runs from the 1930 to the 1948 model year. But Flathead describes more than those large engines. The 45-cubic-inch engine served other motorcycles and continued in the Servi-Car through 1973. The arrival of a new engine did not mean that every size of the older design disappeared at once. 1, 3
V-series Flathead Big Twin, model years 1930–1936.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0U-series Flathead Big Twin, model years 1937–1948.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0The 45 family — From the civilian WL to the wartime WLA
Another essential branch of the Flathead story is the 45-cubic-inch engine, approximately 750 cc. It has a history of its own alongside the V- and U-series Big Twins.
The civilian WL was on the market from 1937. It was adapted for military service as the WLA, with equipment including blackout lighting, an oil-bath air cleaner and luggage provisions. The WLC was configured to Canadian military requirements. These three names describe different roles and specifications within the same engine family. 16, 17
Following trials in 1939, limited WLA production began in 1940. It became an important military motorcycle during World War II, carrying messages, helping control convoys and serving military police, rather than primarily charging into front-line combat. Wartime production ended in 1945, with production resuming from 1949 to 1952. 17, 18
There is a detail worth remembering when examining an old example: the 42WLA prefix does not prove that every motorcycle carrying it was actually built in 1942. The prefix was used across wartime production years, so establishing a bike’s history requires other evidence too. 17
The wartime period also brought the 1942-model XA, with a horizontally opposed twin-cylinder engine. Its layout is visibly different from the WLA’s V-twin, even though both belong to the military motorcycle story. The XA is a separate branch and should not be grouped under WLA. 19
An engine representing the Flathead 45 family, also used by the WL line; it is not identified as a WLA engine of a specific year.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A complete 1942-model WLA, showing its military equipment.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0The 1942 XA’s horizontally opposed twin, distinct from the WLA’s V-twin.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01936–1947 — Knucklehead lays the foundations for the modern Big Twin
The year 1936 marked an important turning point. Harley-Davidson introduced an overhead-valve, or OHV, Big Twin, placing the valves in the cylinder heads and operating them through pushrods and rocker arms.
The rocker covers resembled knuckles or a clenched fist, inspiring riders to call the engine the Knucklehead. A name drawn from its appearance came to describe an entire Harley era.
Its importance lies in being the company’s production OHV V-twin and in establishing the direction of subsequent Big Twins. Harley had already built OHV racing engines and singles, so the milestone belongs specifically in the context of V-twins sold for ordinary road use.
Look at later Big Twins and the ideas made clear in the Knucklehead era remain visible: cylinders arranged in a V, pushrods alongside them and valves above the combustion chambers. Much of the internal engineering has changed, but the outline of that approach endures. 4
Knucklehead, model years 1936–1947, named after the shape of its rocker covers.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01948–1965 — Panhead makes everyday use easier
For the 1948 model year, the Panhead succeeded the Knucklehead with aluminium cylinder heads and hydraulic valve lifters. These helped reduce operating noise and the need for valve adjustment.
The nickname came from rocker covers shaped rather like pans or trays. Once again, riders named an engine after something they could see, and the name became part of the shared language of Harley enthusiasts.
The Panhead is a useful chapter in understanding Big Twin development. Improving an engine was not just about adding power. Quieter operation, easier maintenance and sustained everyday use were part of the process too. 1, 5
Panhead, model years 1948–1965, with pan-shaped rocker covers.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01966–1984 — Shovelhead and the expanding world of Big Twin
The Shovelhead arrived for the 1966 model year with revised cylinder heads and improved performance over its predecessor. Its name came from rocker covers whose shape suggested a coal shovel.
This was also a period when Big Twins appeared in an increasingly varied range of motorcycles. The Super Glide’s arrival in 1971, followed by bikes such as the Low Rider, gave Harley’s large engines a broader home beyond touring motorcycles.
For riders drawn to older bikes, the Shovelhead connects the traditional engine silhouette with motorcycles developing more distinct personalities: long-distance machines, bikes with a sportier stance, and motorcycles owners would reshape to reflect their own style.
The date to remember is 1966, the Shovelhead’s first model year. The 1965 Electra Glide still belonged to the Panhead era. Matching model names with engine years makes a motorcycle’s history much easier to read accurately. 5
Shovelhead began with the 1966 model year, not 1965.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01984–1999 — Evolution opens a new chapter for Harley-Davidson
Evolution was an apt name for the direction Harley took. For the 1984 model year, the company stayed with an air-cooled, pushrod-operated 45-degree V-twin while improving materials and manufacturing details for a new era of use.
The 80-cubic-inch Big Twin, approximately 1,340 cc, used aluminium cylinders and heads, with improved control of oil leakage. Durability and reliability became central to the Evo’s reputation.
Its arrival followed the management buyout from AMF in 1981. With limited resources, Harley had to choose which projects to pursue. It committed to developing its traditional V-twin into the Evolution.
Looking back, the Evo marks a turning point in both engineering and company direction: a familiar engine concept prepared to carry Harley into another era.
There is an important distinction behind the shared name: Evolution Big Twin and Evolution Sportster are different engine families. We will return to the Sportster after following the Big Twin line to the present. 1, 5
The 80-cubic-inch Evolution Big Twin, introduced for the 1984 model year.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.01999–2017 — Twin Cam and the two-cam era
The Twin Cam took over in the Big Twin line for the 1999 model year. This time the name referred directly to internal architecture: two camshafts, rather than the shape of an engine cover.
It began at 88 cubic inches, with other capacities following over the family’s lifetime. Cylinder heads, intake and exhaust passages, performance-related details and emissions control continued to develop.
The B-version engines also used counterbalancing for Softails with rigidly mounted engines. This is another example of an engine name covering different specifications depending on the motorcycle. When assessing a used bike or planning modifications, knowing that it has a Twin Cam is only the beginning. The year, motorcycle model and engine designation matter too. 1
Twin Cam: the Big Twin family with two camshafts.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Twin Cam / Rushmore: a development within the Twin Cam family.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.02017–present — Milwaukee-Eight: eight valves in two cylinders
The Milwaukee-Eight, or M8, was announced in August 2016 for 2017-model Touring and Trike motorcycles. That explains why some sources give 2016 as the launch year while engine timelines commonly begin at the 2017 model year.
Eight refers to the total valve count: four valves per cylinder. The engine retains the 45-degree cylinder angle but returns to a single camshaft, alongside further development of counterbalancing and heat management.
Returning to one camshaft after the Twin Cam era shows why the number of components alone cannot measure engineering progress. The whole system matters, from airflow and combustion to rider comfort.
Cooling arrangements vary between M8 applications, with some using liquid-assisted cooling around the cylinder heads. The specification of the individual engine and motorcycle should therefore be checked rather than assuming that every M8 uses the same system. 6
Milwaukee-Eight: four valves per cylinder, eight valves across the two cylinders.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A parallel story — From Model K to Sportster
While Big Twin moved through the Knucklehead, Panhead and Shovelhead eras, another motorcycle line was taking shape.
The Model K appeared in 1952 with a 750 cc side-valve V-twin. It laid the foundations for the XL Sportster, which followed in 1957 with an OHV engine and cast-iron cylinder heads, the origin of the Ironhead nickname.
The Sportster places its engine and transmission in a shared casing, an arrangement known as unit construction. This is an important distinction from traditional Big Twins. Small Twin, as used in riders’ conversations, is better understood as a convenient grouping than as a category determined solely by displacement.
The Ironhead remained in the Sportster line through the 1985 model year. Evolution Sportster followed in 1986, initially in 883 and 1100 cc versions, with 1200 cc arriving later. The family remained in the motorcycle range through the 2022 model year.
When someone says Evo, it is worth asking which one: Big Twin or Sportster. The answer points to different motorcycles, engine layouts and maintenance needs. 1, 7
The complete 1952 Model K motorcycle, illustrating the foundations of the Sportster story.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Ironhead Sportster, model years 1957–1985.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Evolution Sportster, model years 1986–2022; a different engine family from Evolution Big Twin.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Small motorcycles and Aermacchi — Another side of Harley history
A history told only through twins would leave out another interesting part of Harley-Davidson’s story.
Between the earliest singles and the small post-war motorcycles came the A/B-series singles, introduced in 1926 in side-valve and OHV forms. The OHV single-cylinder racer known as the Peashooter also shows that Harley used overhead valves before the Knucklehead. Separating road-engine history from racing-engine history matters here. 20, 21
The company returned to small motorcycles with a 125 cc two-stroke in 1948, developing that group further in the years that followed. These American-built post-war machines should be distinguished from motorcycles produced by Aermacchi in Italy.
In 1960, Harley-Davidson invested in Aermacchi’s motorcycle business. The 1961 Sprint became the first Harley model made by the Italian company, bringing smaller motorcycles into gaps in the range.
The Sprint’s four-stroke single has a distinctive appearance, with its cylinder lying almost horizontally. The Italian range also included small two-strokes. Harley’s relationship with the Aermacchi business ended when it was sold to the Castiglioni brothers in 1978.
The 1960–1978 span on the timeline therefore describes a business relationship, not the production life of one engine. These motorcycles deserve a place in Harley history because they show the effort to reach riders seeking smaller, lighter bikes for different kinds of use. 7, 8, 9
The Topper, built from 1960 to 1965, was another kind of small Harley: a single-cylinder two-stroke scooter. Its bodywork and drivetrain differ clearly from those of a Sprint, and it should not be treated as part of the Aermacchi range. 22
A complete 1927 Peashooter, an OHV single-cylinder racer.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A two-stroke single from Harley’s American-built small-motorcycle range.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0The four-stroke Sprint engine from the Aermacchi line.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A complete 1976 SX-250, an example of an Italian-built two-stroke.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A complete 1960 Topper, Harley-Davidson’s two-stroke scooter.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.02002–2017 — Revolution: V-Rod takes another route
With the V-Rod’s arrival for the 2002 model year, Harley-Davidson introduced the Revolution, an engine markedly different from traditional Big Twins and Sportsters.
This V-twin uses a 60-degree cylinder angle, double overhead camshafts, four valves per cylinder and liquid cooling, with Porsche involved in its development.
Revolution deserves its own route through Harley engine history, alongside the V-Rod name and VRSC model family. It should not be presented as a replacement for the Twin Cam: both were sold during overlapping periods and served different styles of motorcycle. 1, 10
Revolution for V-Rod: a liquid-cooled V-twin.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.02014 — Revolution X for Street 500 and Street 750
Before Revolution Max came Revolution X, powering the Street 500 and Street 750. The motorcycles were announced in late 2013 and began reaching the market in 2014.
These liquid-cooled engines powered motorcycles developed for newer riders and urban travel. They represented another way to broaden Harley’s audience beyond large Big Twins.
Revolution, Revolution X and Revolution Max should be kept distinct when reading motorcycle specifications. Similar names do not make them the same engine family. 11
Revolution X for Street 500/750, introduced for the 2014 motorcycle range.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.02021–present — Revolution Max and a new Sportster chapter
Revolution Max reached production motorcycles in 2021, in both Pan America and Sportster S. This liquid-cooled, 60-degree V-twin uses DOHC and variable valve timing, and is designed to act as a stressed member of the motorcycle’s structure.
Sportster S uses the Revolution Max 1250T, while the Nightster, introduced in 2022, uses the 975T. The change connected the Sportster name to another engine architecture after decades with air-cooled OHV powerplants.
In the history of the motorcycle line, Ironhead, Evolution Sportster and Revolution Max can be told as successive chapters. In terms of engine architecture, Revolution Max belongs among the modern families, not least because it also powers Pan America.
This is where model lineage needs to be distinguished from engine family. The Sportster name can continue even when the heart of the motorcycle has changed substantially. 12, 13, 14
A Revolution Max 975T in a Nightster; this is not the Sportster S’s 1250T engine.
Photo: Chris Woodrich · Wikimedia Commons · CC BY-SA 4.0Racing engines — A route running alongside the road bikes
Racing engines have their own place beside the road-bike timeline. Introduced in 1916, the Eight-Valve was an OHV racing V-twin with eight valves approximately a century before Milwaukee-Eight. They are, of course, different engine families. 23
The Two-Cam name also appeared in the F-head era, long before the 1999-model Twin Cam. The 1924 FH racer pictured in this article is one example. Similar names alone do not identify the same engine design. 24
Later came the side-valve WR/WRTT and KR/KRTT racing lines. The 1952-model KR was an important milestone before the XR-750 entered competition in 1970. The XR developed from its early iron-head version into an aluminium version and continued racing through 2024. That span describes longevity in competition; it does not mean new engines were manufactured every year throughout it. 23, 25, 26
Liquid-cooled racing engines also predate V-Rod. The VR1000 entered Superbike competition in 1994. The XG750R, introduced to racing in 2016, uses the Street 750’s Revolution X as its foundation and remains part of the American Flat Track story covered by the Thai original. These engines deserve space of their own, showing the relationship between competition engineering and the motorcycles riders buy. 27, 28, 29
The Eight-Valve racer, introduced in 1916; a different family from today’s Milwaukee-Eight.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A complete 1924 FH Two-Cam racer; this name does not identify the 1999 Twin Cam family.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0A complete 1956 KR Dirt Racer, powered by a side-valve twin.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0XR-750: introduced in 1970 and raced through 2024.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0VR1000: the liquid-cooled Superbike programme engine.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Regional-market motorcycles and related engines
A worldwide view of modern Harley-Davidson also needs to include the X350 and X500, documented for the 2023 model year with liquid-cooled parallel-twin engines. The X440, launched in India in 2023, uses an air- and oil-cooled single. These belong in distinct groups from Big Twin, traditional Sportster and the Revolution V-twins. 30, 31
Buell engines such as the Blast belong in the context of related brands and engineering. Nova belongs in the story of prototype engines, while LiveWire belongs in the history of electric propulsion. Including these subjects broadens the picture while keeping the boundaries of the main engine families clear. 5, 20
The Buell Blast engine illustrates a related brand, separately from motorcycles bearing the Harley-Davidson name.
Photo: Michael Barera · Wikimedia Commons · CC BY-SA 4.0Read the engine, and you can read more of the motorcycle
Place these engines on a timeline and Harley-Davidson becomes a collection of stories unfolding together. Big Twin carries forward ideas from earlier eras. Sportster develops along another route. Small motorcycles welcome new kinds of rider, while liquid-cooled engines take the brand into different kinds of motorcycle.
The appearance-based nicknames of Knucklehead, Panhead and Shovelhead make engineering history something riders can see and remember. Evolution, Twin Cam and Milwaukee-Eight reflect other ways of describing change through the years.
Next time you stand beside a Harley, start with the engine at the centre of its frame. Look at the cylinder heads, pushrods and transmission layout, then match them to the model and year. There may be more to talk about than tank colour, exhaust pipes or the displacement written on a cover.
That is the starting point of The History: getting to know the motorcycles we enjoy through the people and machines that made them Harley-Davidson.
Engine eras at a glance
Model years are used where applicable. Announcement years, racing milestones and periods of business cooperation are identified separately.
| Family / group | Dates | Architecture | What to look for |
|---|---|---|---|
| Early single | 1903–1918 | F-head single | The starting point before V-twins 1, 2 |
| Early V-twin / F-head | 1909; improved version 1911–1929 | 45° V-twin | Foundations before the later Big Twin line 1 |
| Sport Twin / Model W | 1919–1923 | Horizontally opposed twin | Neither Sportster nor the later WL 15 |
| A/B singles and Peashooter | 1926–1934; racer pictured: 1927 | Side-valve / OHV single | OHV engines existed in some groups before Knucklehead 20, 21 |
| Flathead 45 / WL–WLA–WLC | Family: 1929–1973; WL from 1937 | 45 ci side-valve V-twin | Wartime WLA production: 1940–1945; resumed 1949–1952 1, 16, 17, 18 |
| V/U Flathead Big Twin | V: 1930–1936; U: 1937–1948 | 74/80 ci side-valve V-twin | Separate from the 45-cubic-inch family 1, 3 |
| Knucklehead | 1936–1947 | OHV V-twin | Production OHV Big Twin 4 |
| XA | 1942 | Horizontally opposed twin | A military branch distinct from WLA 19 |
| Panhead | 1948–1965 | OHV V-twin | Aluminium heads / hydraulic lifters 1, 5 |
| American small two-strokes / Topper | Small bikes: 1948–1966; Topper: 1960–1965 | Two-stroke single | Separate from the Aermacchi line 1, 22 |
| Model K/KH | From 1952; before Sportster in 1957 | Side-valve V-twin | Foundations of the Sportster line 7 |
| Ironhead Sportster | 1957–1985 | OHV V-twin | Cast-iron cylinder heads 7 |
| Aermacchi | Business relationship: 1960–1978 | Four-stroke and two-stroke singles | A business period, not the life of one engine 8, 9 |
| Shovelhead | 1966–1984 | OHV V-twin | First model year: 1966 5 |
| Evolution Big Twin | 1984–1999 | 80 ci OHV V-twin | Separate from Evolution Sportster 1, 5 |
| Evolution Sportster | 1986–2022 | OHV V-twin | Sportster unit construction 7 |
| Twin Cam | 1999–2017 | OHV V-twin / two camshafts | Includes developments within the family, such as Twin-Cooled 1, 5 |
| Revolution / V-Rod | 2002–2017 | Liquid-cooled DOHC V-twin | VRSC / V-Rod engine family 10 |
| Revolution X | Motorcycle range introduced for 2014 | Liquid-cooled V-twin | Street 500 / Street 750 11 |
| Milwaukee-Eight | From model year 2017 | OHV V-twin / eight valves | Cooling arrangements vary by application 6 |
| Revolution Max | From 2021; Nightster from 2022 | Liquid-cooled DOHC V-twin | Pan America, Sportster S and Nightster 12, 13, 14 |
| X350 / X500 / X440 | From 2023 | Parallel twins / single | Regional-market bikes, separate from Big Twin 30, 31 |
| Racing engines | Eight-Valve: 1916; KR: 1952; XR750: 1970; VR1000: 1994; XG750R: 2016 | Multiple architectures | First years of individual engines, not one combined production span 23, 25, 26, 27, 28 |
Photo credits & references
Written for HD-Playground using multiple sources. This English edition is translated and adapted from the Thai article, rather than from any single external publication.
All photographs are licensed under CC BY-SA 4.0 Photographs on this page have been resized and converted to WebP without cropping or colour adjustment. Follow each source link for the original image and licence details. The family map and tables were prepared for this article.
Credits for all 33 photographs
| Photo | Subject / context | Photographer | Source / licence |
|---|---|---|---|
| 01 | Early Single An early single-cylinder engine representing the 1903–1918 family; the exhibit does not establish that this particular engine dates from 1903. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 02 | F-head V-Twin The improved F-head V-twin introduced in 1911. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 03 | V-Series Flathead V-series Flathead Big Twin, model years 1930–1936. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 04 | U-Series Flathead U-series Flathead Big Twin, model years 1937–1948. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 05 | Knucklehead Knucklehead, model years 1936–1947, named after the shape of its rocker covers. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 06 | Panhead Panhead, model years 1948–1965, with pan-shaped rocker covers. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 07 | Shovelhead Shovelhead began with the 1966 model year, not 1965. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 08 | Evolution Big Twin The 80-cubic-inch Evolution Big Twin, introduced for the 1984 model year. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 09 | Twin Cam Twin Cam: the Big Twin family with two camshafts. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 10 | Milwaukee-Eight Milwaukee-Eight: four valves per cylinder, eight valves across the two cylinders. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 11 | Ironhead Sportster Ironhead Sportster, model years 1957–1985. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 12 | Evolution Sportster Evolution Sportster, model years 1986–2022; a different engine family from Evolution Big Twin. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 13 | Two-cycle Single A two-stroke single from Harley’s American-built small-motorcycle range. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 14 | Aermacchi Sprint The four-stroke Sprint engine from the Aermacchi line. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 15 | Revolution / V-Rod Revolution for V-Rod: a liquid-cooled V-twin. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 16 | Revolution X Revolution X for Street 500/750, introduced for the 2014 motorcycle range. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 17 | Revolution Max 975T A Revolution Max 975T in a Nightster; this is not the Sportster S’s 1250T engine. | Chris Woodrich | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 18 | 1952 Model K The complete 1952 Model K motorcycle, illustrating the foundations of the Sportster story. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 19 | 1909 Model 5-D A 1909 Model 5-D displayed alongside a 1906 single-cylinder motorcycle. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 20 | Flathead 45 / WL family An engine representing the Flathead 45 family, also used by the WL line; it is not identified as a WLA engine of a specific year. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 21 | 1942 WLA A complete 1942-model WLA, showing its military equipment. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 22 | Sport Twin / Model W Sport Twin / Model W, 1919–1923: a separate branch from Sportster. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 23 | XA The 1942 XA’s horizontally opposed twin, distinct from the WLA’s V-twin. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 24 | Eight-Valve racer The Eight-Valve racer, introduced in 1916; a different family from today’s Milwaukee-Eight. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 25 | 1927 Peashooter A complete 1927 Peashooter, an OHV single-cylinder racer. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 26 | 1924 FH Two-Cam racer A complete 1924 FH Two-Cam racer; this name does not identify the 1999 Twin Cam family. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 27 | 1956 KR racer A complete 1956 KR Dirt Racer, powered by a side-valve twin. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 28 | XR-750 XR-750: introduced in 1970 and raced through 2024. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 29 | VR1000 VR1000: the liquid-cooled Superbike programme engine. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 30 | Twin Cam / Rushmore Twin Cam / Rushmore: a development within the Twin Cam family. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 31 | 1976 SX-250 / Aermacchi A complete 1976 SX-250, an example of an Italian-built two-stroke. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 32 | 1960 Topper A complete 1960 Topper, Harley-Davidson’s two-stroke scooter. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
| 33 | Buell Blast (related) The Buell Blast engine illustrates a related brand, separately from motorcycles bearing the Harley-Davidson name. | Michael Barera | Wikimedia Commons ↗ CC BY-SA 4.0 |
31 content references
The Thai original was compiled from multiple sources. Engine dates generally use motorcycle model years, which may differ from calendar-year announcements. Family timelines overlap and can vary by model or market.