Knucklehead, Flathead, Shovelhead, Evolution and More: Harley-Davidson Engines since 1909

If you ride a Harley or would like to someday, knowing a thing or two about the evolution of the company’s iconic V-twin engines is pretty important. You’ll need that knowledge to help you maintain your street cred, or at least keep you from needing to lip-sync the song Tequila in a biker bar. (If you don’t get it, don’t ask.) Want to learn the actual differences between a Knucklehead, Panhead, or Twin Cam 96 and why you should care? Read on.

The Harley-Davidson V-twin engine is nearly as storied as the company that created it. The angled engine cylinders set at 45 degrees first appeared commercially on Harleys in 1909, but the design was a flop at first. Only a few dozen were ever built. The automatic intake valves were designed for single-cylinder engines and caused problems with the flow characteristics. It took some tweaking, the addition of mechanical intake valves, and a new frame before the V-twin found success in 1911.

A Brief History of Engine Names

Through the years Harley motors have increased in displacement and sophistication, but the Big Twins have always kept some things in common. All Big Twin Harleys have been longitudinally-mounted, air-cooled, 45-degree V-twins with large displacements. Not all Harley models have been Big Twins, but most of the longest running and most memorable are. Several Big-Twin engines earned nicknames based on their appearance while others go by their official factory names.

F-Head (1911 to 1929)

These were some of the first V-twins, and they get their name from the shape of the intake tract determined by the location of the valves.

Flathead (1929 to 1939)

Harley-Davidson Flathead Engine


A flathead or a “sidevalve” doesn’t have valves in the cylinder head, but rather has them set off to the side. The name flathead, oddly enough, came from the flat shape of the heads on top. First built in 1929, it was a 45-cubic-inch WL sidevalve with twin bullet headlights. A 74-cubic-inch version was introduced in 1930. The engine was still used in the three-wheeled Servicecar until 1974.

Knucklehead (1936 to 1947)

The knucklehead was Harley-Davidson’s first production motorcycle with overhead valves and a re-circulating oil system. Originally introduced with a engine displacing 61 cubic inches, it increased to 74 cubic inches by 1941. The UL and ULH models got an 80-cubic-inch engine from 1936 until 1945. The name comes from the curving shape of the rocker covers, which sort of resemble the knuckles on a fist.

Panhead (1948 to 1965)

The Panhead engine emerged as World War II was ending. It was the beginning of a new generation of Big Twins, and while the engine kept the overhead valves of the Knucklehead, it now included aluminum cylinder heads and hydraulic valve lifters. It was available in 61 and 74-cubic-inch versions. It was also the first Harley to feature an electric starter instead of a kick starter with the 1965 Electra Glide model. The engine’s name comes from the pan-like shape of the valve covers.

Shovelhead (1966 to 1985)

Harley-Davidson Shovelhead Engine


The first Shovelhead engines were introduced in 1966, with the first models at 74 cubic inches. Later some models would grow to 80 inches by 1979. They featured cast aluminum rocker boxes to replace the leaky sheet metal used in the Panhead and had a Tilotson carburetor and PowerPak heads to give up to a 15 percent increase in power. The shovel shape of the engine’s cylinder heads is the culprit behind the name.

In 1980 the Sturgis became the first modern Harley model to have a belt final drive as opposed to the louder chain. It also lasted longer and needed fewer adjustments and no lubrication. That same year the FLT Tour Glide model was introduced with three elastomer rubber mounts. They allowed the engine to shake without shaking the rider by isolating the vibration between the frame and rider.

Evolution (1984 to 1999)

The Evolution, “Blockhead” or “Evo” as it’s most commonly called, was the engine that brought Harley-Davidson back in a big way. The engine displaced 80 cubic inches or 1340 cc, but was constructed with steel-lined alloy cylinders with new pushrods, pistons and cylinder heads. Although it had the same displacement as its predecessor, it created significantly more torque and horsepower.

Twin Cam 88 (1999 to 2006)

It’s no stretch of the imagination to arrive at the name for the Twin Cam 88. The 88-cubic-inch (1450cc) engine featured two camshafts. In the FL and Dyna models, the engine was rubber mounted to isolate the vibration from the rider, and in 2000, Harley-Davidson introduced the 88B version, which only came in the Softail models. It had twin counterbalancers, which are weights that turn opposite to the engine’s crankshaft, to cancel out engine vibration before it reaches the frame. This is easier on bike parts as well as the rider. The counterbalancers allow the engine to be mounted solidly to the frame, which results in a much stronger frame. It also allows the frame to fit more closely to the engine for a classic look.

V-Rod (2002 to the present)

 Harley-Davidson V-Rod Engine

The V-Rod was a distinctive shift from anything Harley-Davidson had done in the past. The company teamed with German automaker Porsche to develop a new V-twin. Beyond the modern styling, an obvious difference included having the cylinders separated 60 degrees apart, not 45, to allow for a lower motorcycle design and increased space for mounting fuel injectors and the air box. The engine displaced 1130cc, and while the rear-wheel horsepower was 106, the torque was only 72 lb-ft, which indicated a revving engine rather than a torque engine like the classic Big Twins. Some newer models were increased to 1250cc.

Twin Cam 96 (2007 to the present)

Twin Cam 96 Engine 

While very similar in appearance to the Twin Cam 88, the Twin Cam 96 has, go figure, displacement of 96 cubic inches (1584cc). The increased displacement was achieved by increasing the stroke from 101.5 mm to 111.25mm while using the same 95.2 mm bore. This change increased the compression ratio from 8.9 to 9.2:1. New Big Twin engines also got a new six-speed transmission replacing the old five-speed. And starting in 2007 all Harley models are fuel injected.

Now that you know a thing or two about Harley engines, why not check out our selection of biker gifts and accessories on our shop pages?

And if you'd like to learn more check out the book “Everything You Need to Know Harley-Davidson Motorcycles” by Bill Stermer (2007)