What Does FLH Stand For On Harleys?

Are you a Harley-Davidson biker and curious about the term “FLH” and want to know what it stands for? If yes, then this is certainly the right place for you to be.

FLH refers to Harley-Davidson’s Touring models with large front forks (FL) and a heavier frame designed for long-distance riding, such as the Electra Glide series.

In this article, you will get to know all about Harley-Davidson FLH, what does FLH stand for on Harleys, the origin and history of the Harley-Davidson FLH Series, and more. Stick around to get all the answers that you are looking for.

What Does FLH Stand For On Harleys?

The Harley-Davidson FLH lineup is incredibly popular and one of the longest mainstays in Harley-Davidson’s touring category. Introduced back in the 1940s, the Series delivered numerous “firsts”, laying the groundwork for most present-day Harley-Davidson tourers. Given its major influence on the segment, it’ll be quite interesting to know more about the Harley-Davidson FLH’s history, evolution, and model progression.

The FLH identifier in Harley-Davidson bikes can mean one of these two things. First, it can pertain to “Hydra-Glide”, with the first variation of it being FLH Harleys. Secondly, it can also signify “high compression”, which refers to the motorcycle’s bumped-up horsepower of 60 HP. The meaning goes with the suffix, depending on its version.

While recent models like the Harley-Davidson Street Glide FLHX and Harley-Davidson Road Glide FLTRX are known by the general public, the older Harley-Davidson FLH models boast a more compelling presence that helped them get the reputation of being some of the best bikes of all time.

The Harley-Davidson FLH bike, manufactured by the Milwaukee-based motorcycle company, originated in 1949 as the Hydra-Glide touring model, naming it for its hydraulically damped telescopic forks. Since the introduction of Hydra-Glide, bikes like Duo-Glide, and Electra-Glide models also got produced and carry the FLH designation. The FLH bikes continue in 2009 as Electra-Glides. 

All Harley-Davidson Touring bikes, equipped with the large Big-Twin engines and large telescopic forks, are known as the FL models. They come with the letters “FL”, which was a simple series designation that was started in 1941. These motorcycles were powered by the company’s famed 1937-47 Knucklehead engine. It got its name for its rocker covers having an odd shape. The “Panhead” engine got introduced in 1948, named after the new shape of the rocker cover. The following year, the Harley-Davidson FLH model was produced.

The Origins of the Harley-Davidson FLH

The Harley-Davison FLH, manufactured by the motorcycle giant, belongs to one of Harley-Davidson’s touring lineups. This series originated in 1941  it fell under the FL designation. The lineup came into its own in 1949 with the launch of the Harley-Davidson Hydra-Glide model. This bike got its name after its hydraulically damped telescopic forks.

Later, two other models named Harley-Davidson Duo-Glide and Harley-Davidson Electra Glide got released in the market later on. The FLH Harleys also had changes to the engine design, alongside many remarkable upgrades throughout the lineup’s production run.

The first FLH made

The 1949 Harley-Davidson FLH Hydra-Glide came powered by a 74-cubic-inch two-cylinder pushrod V-twin engine. The bike was dubbed the “Hydra-Glide” due to its new front suspension system, which sat on a 59.5-inch wheelbase. The hydraulic technology gives the Harley-Davidson FL series its “H” designation. The year 1951 saw the Hydra-Glide bikes operating with a hand-shift and foot-clutch. The configuration got reversed for 1952, with a hand-clutch and foot-shift. The foot-shift versions of the bike were identified as FLHF.

Updates to the FLH lineup

The 1955-57 Harley-Davidson FLH still sported a 74-cubic-inch engine, which was combined with polished ports and high-compression heads to generate 55 HP. Its wheelbase got stretched slightly by almost a half inch. Buyers will still be able to find the old-style foot-clutch, hand-shift models as a viable option through 1978.

1958 brought forth a new frame featuring a rear swing arm that was suspended by two coil-over-shock suspension components. This new suspension helped earn the FL Series the moniker of “Duo-Glide” as it replaced the Hydra-Glide. The Duo Glide got renamed as an FLH model.

The 1958-65 Harley-Davidson Duo-Glide still remains one of Harley’s most beautiful motorcycles, with a near-perfect combination of the Panhead engines and frame flourishes. It came with an unusual speedometer, which dropped the zeroes to read 1-12 to eliminate clutter. It was equipped with a chromed oil tank, a dual fishtail exhaust, a kick-start pedal, and handle grips. Even though the new model featured a new rear suspension, it still came with a superfluous sprung seat.

The “Shovelhead”, named after the shape of the bike’s rocker covers, replaced the Panhead in 1966 with the 1200cc engine being upgraded in 1978 to 1340cc. The year before the Shovelhead debuted, the Electra-Glide got introduced and came with an electric starter, eliminating the need for the kick-start feature. Using the same 74-cubic-inch engines as the previous models, the Shovelhead got boosted to 60 HP.

The Harley-Davidson FLH Electra-Glide replaced the Harley-Davidson Duo-Glide. An unfaired version of the bike, which is essentially a partially covered front of the bike, got produced from 1977 to 1982. as the Harley-Davidson FLHS Electra-Glide. The Harley-Davidson FLHR Road King officially debuted in 1994, and it still remains in production.

History of the Harley FLH Engines

Before the inception of Harley-Davidson FLH models, the original FL bikes were equipped with an engine version called the “Knucklehead” or Harley Fist. This power mill featured an OHV-pushrod design, knuckle-shaped rocker boxes, and a piston displacement of 1,210 cm³ (73.8 in³). Knuckleheads were used on Harley-Davidson’s large-frame two-wheelers for another 7 years.

By 1948, the Knucklehead got replaced by “Panhead” power mills. These engines were redesigned and included aluminum cylinder heads and self-adjusting hydraulic lifters. Due to the improvements made, this engine version was in use until 1966, and it covered all Harley-Davidson Hydra-Glide and Harley-Davidson Duo-Glide models.

Panhead carried over to the first year of Electra-Glide models before it got switched to “Shovelhead” engines. The new power mills became the new standard with electric starters and a larger 1,300cc displacement in 1978. 

The improved piston displacement got made available alongside the 73.8 in³ before the latter got discontinued 3 years later. For each version of the engine, significant enhancements got introduced and made standard. Here are some of the accompanying benefits of each engine type –

Knucklehead (1941 – 1947)

• The Knucklehead engine sported a distinctive valve shape cover, making it easy for enthusiasts and owners to classify this engine 
• It put an end to the problematic side valve or the “Flathead” engine preceding it 
• Featured considerable design improvements rectifying the valve spring breakage, top-end oil leakage linked to 1931 and earlier versions, and poor rocker lubrication 
• The engine design incorporated a pumped or dry sump recirculating oil system instead of the drip feed system 

Panhead (1948 – 1966)

• The new engine design helped in overcoming overheating problems that were associated with Flatheads 
• The Hydraulic clearance adjusters got incorporated into the top portions of the pushrod, and it led to offsetting of the aluminum heads’ increased heat expansion and reduced need for valve clearance adjustment 
• The cooling material of the cylinder head also got changed from cast iron to aluminum, which gave the engine thrice its capacity for heat conductivity 
• The models starting from 1955 boasted a 60 HP power output and new top-end cases having sturdier main bearings 
• Single-piece valve covers were introduced to solve oil containment problems, whereas felt blanket-covered rocker gears helped reduce valve noise
• The penultimate year of the engine for Harley-Davidson FLH saw increased horsepower and a higher compression ratio (although it wasn’t enough to yield a decent power-to-weight ratio for the near 800-pound two-wheeler)

Shovelhead (1966 – 1984)

• The Shovelhead supported increased weight, which resulted from the inclusion of revised rear suspension and the addition of an electric start, while also maintaining premium motorcycle performance 
• The 1969 models and onward featured generators replaced with alternators
• Shallower combustion chambers helped aid in cooling the engine and performed well with higher compression ratios 
• By 1970, the kick-start feature got removed from all Harley-Davidson bikes with an FL designation 
• At the beginning of the 80s, countermeasure parts were produced for offsetting oil consumption and other issues that resulted from the sub-par quality of engines manufactured in the late 1970s
• The engine was redesigned such that it could tolerate higher-than-stock compression ratios and be more compatible with low-lead fuel variants after 1977
• A redesigned chassis, a final belt drive, and a new 5-speed gearbox got adopted, beginning with the 1980 Harley-Davidson FLH.

History of the Harley-Davidson FLH Variations

For Harley-Davidson bikes, the first letter (sometimes even the first two letters) designates the type of engine, the frame, and the front end of the motorcycle. However, for FLH Harley-Davidson bikes, in particular, the name of the bike changed while the suffix remained the same.

Technology enhancements customarily signified by changes to the latter got reflected in the name part instead. This was also the first time for the Milwaukee motorcycle giant to deviate from using an alpha system when naming its bikes. Between 1941 and 1984, three variations got manufactured under the FLH designation – the Harley-Davidson Hydra-Glide, the Harley-Davidson Duo-Glide, and the Harley-Davidson Electra-Glide.

Harley-Davidson Hydra Glide (1949 – 1957)

The Harley-Davidson Hydra Glide came with a 1200cc displacement and a 7.0:1 compression ratio. Further, it ran at a top speed of 100 mph and spewed 50 HP (36.8 kW) at 4,800 RPM. This bike came equipped with a Panhead engine with a hand shifter and foot clutch.

By 1952, the clutch-shifter configuration got reversed. The following year, refinements to the motorcycle’s power mill resulted in improved performance figures of 60 HP (44.1 kW) at 4,800 RPM and a top-speed rating of 105 MPH (169 km/h).

Harley-Davidson Duo Glide (1958 – 1964)

What was new with the production model of Duo Glide was the addition of dual hydraulic rear suspension units with rear brakes and 3-way adjustment. This new variation also featured a sprung seat, which enhanced rider comfort. The engine used here was the Panhead, and it was used until the bike’s final year.

The hand-clutch and foot-shift option that originally supplemented the hand-shifter and foot-cluck mechanism became the new standard in Duo Glide versions. It was also around this time that the FL-suffixed bikes remained the lone large-frame models of Harley-Davidson.

Of the initial Harley-Davidson FLH variations, the Duo-Glide is considered to be among Harley-Davidson’s most beautiful two-wheelers, with a chromed frame and Panhead engine. Conversely, the bike also sported quirky features like a speedometer with the zeroes omitted and a lot more.

Harley-Davidson Electra Glide (1965 – 1979)

The first year of the Harley-Davidson Electra-Glide made use of the Panhead engine, although it had an electric starter. Due to this new technology, the first half of the bike’s name got changed from “Duo” to “Electra”. Further, this particular FLH Harley-Davidson bike necessitated frame modifications for accommodating its 12V battery.

The Electra-Glide was the only variation model that transitioned through two different engine versions. In its second year, the model got equipped with the newer Shovelhead power mill, which gave it a 10% increase in horsepower, among many other benefits.

The “Batwing” fairing would eventually become available on Harley-Davidson Glides in 1969. While the fork-mounted fairing was promising initially as it was easily removable, but later-year iterations weren’t as lucky with this feature. In 1977, Harley-Davidson came out with a Harley-Davidson FLH Electra-Glide Confederate Edition clad in the fender decals, fuel tank, and commemorative paint. Only 44 units of this special-edition motorcycle got produced, which made it hard to come by even in auctions.

Harley-Davidson Electra-Glide Sport (1977 -1984 and 1989 – 1993)

A forerunner to the current Harley-Davidson FLHR, this naked-style motorcycle got released during two different periods. The earlier versions of this bike featured 2-into-1 cigar mufflers, which eventually got changed to same-side dual exhausts for later-year models.

Harley-Davidson FLT vs. Harley-Davidson FLH

Even though the initial Harley-Davidson FLT (or Harley-Davidson Tour Glide) falls under the FL designation, it isn’t actually a Harley FLH model. Perhaps, what makes many bikers think this way is the fact that the motorcycle was sold alongside the Harley-Davidson Electra-Glide in 1980.

However, it is actually a different story for its successor, as the Harley-Davidson FLHT got introduced 3 years after the Tour Glide. The later iteration utilized the FLT frame while also adopting the Harley-Davidson FLH’s batwing fairing.

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