FL is a model designation used on motorcycles manufactured by Harley-Davidson from 1941 to present. Mostly applied to Harley's large-framed bikes, including the current Touring series, the FL designation is also used with their Softail series, especially on Softails with traditional styling, 16" front wheels, and either Springer forks or large-diameter telescopic front forks.
Early FL models
The FL was introduced to the Harley-Davidson model line in 1941. It used a 74 cu in (1,210 cc) version of the "Knucklehead" OHV engine that powered the EL in 61 cu in (1,000 cc) form. The FL shared its frame with the EL and with the U and UL, which used a 74 cubic inch flathead engine. The FL replaced the UH and ULH, which used the same frame with 80 cu in (1,300 cc) flathead engines.
The FL continued relatively unchanged until 1948, when it and the EL were given redesigned "Panhead" engines of the same capacities as before. These engines had several improvements over the earlier "Knuckleheads", including aluminium cylinder heads to reduce weight and improve cooling and self-adjusting hydraulic lifters. The U and UL flathead twins were discontinued in 1948, leaving the OHV EL and FL models as Harley-Davidson's large-frame motorcycles.
In 1949, a year after receiving the "Panhead" engine, the FL was given a new front suspension and a model name to go along with it. In honor of their first production motorcycle with hydraulically-damped telescopic forks, the FL was officially called the Hydra-Glide. This name would change twice in the history of the basic large-framed FL bikes, each time signalling an improvement in the bike's technology. In addition, the Glide ending would be used on other models, based on both and FL and FX formats.
In 1952, the Hydra-Glide's transmission format was reversed from hand-shift/foot-clutch to foot-shift/hand-clutch, although the original format continued to be offered as an option until 1978. 1952 was also the last year of the 61 cu in (1,000 cc) EL, making the FL the last remaining large-frame model.
A more highly-tuned engine with high-compression heads, higher-lift cams, and polished ports, was offered with the FLH version of 1955. The FLH designation has continued up to the present.
The FL model was given a new frame in 1958. This frame included a rear swingarm suspended by a pair of coil-over-shock suspension units. In honour of this fully-suspended chassis, the FL's model name was changed from Hydra-Glide to Duo-Glide.
Unlike OHV configuration, aluminium heads, and telescopic-fork front suspension, however, this improvement in technology was applied to the small-frame bikes first, the K-series having received rear suspension in 1952.
The third and final change given to the name of the basic FL model would occur in 1965, the final year of the "Panhead" engines. These last "Panheads" were the first "big-twin" Harley-Davidson engines to be equipped with electric starters, the Servi-Car having received electric start the year before. This innovation for Harley-Davidson was greeted with the new model name of Electra Glide.
In 1966, the "Panhead" gave way to the "Shovelhead," gaining a ten percent increase in power in the process.
A fork-mounted fairing became available on Electra Glides in 1969. This became unofficially known as the "batwing" fairing. Although the batwing fairing was an easily removable option on early Electra Glides, it was not removable on later machines, as the instruments were moved from the fuel tank into the fairing.
The FL frame was the basis for the 1971 FX Super Glide. The FX mated the FL frame with the forks of the XL Sportster, with buckhorn handlebars and a large fibreglass tailpiece completing the Super Glide specification.
The FL was given a front disc brake in 1972.
The three speed plus reverse option was discontinued in 1977.
An 80 cu in (1,300 cc) engine was made optional on the Electra Glide in 1978. However, the FL designation was not changed as a result. By 1981, the 80 cubic inch engine was the standard engine; the 74 cu in (1,210 cc) engine being discontinued.
The FLT Tour Glide was introduced in 1979. Sold alongside the existing FLH Electra Glide, the FLT had a larger frame with rubber engine mounts, a five-speed transmission, the 80 cu in (1,300 cc) engine, and a frame-mounted fairing. In order that the FLT frame, which was larger and heavier than the large and heavy FLH frame, would handle acceptably, the front forks were given radical steering geometry which had them mounted behind the steering head, with the frame behind the steering head being recessed to allow adequate steering lock.
The FLHT was introduced in 1983. This was an Electra Glide based on the FLT Tour Glide frame, but using the Electra Glide "batwing" fairing instead of the Tour Glide frame-mounted fairing.
Except for the base FLH, all 1984 FLs were equipped with the new rubber-mounted Evolution engine and a five-speed transmission.
All "Shovelhead" engines were discontinued by the 1985 model year. In that year, the four-speed solid-engine-mount FLH was modified to accept rubber mounting and the Evolution engine. The FLH was discontinued in 1986; all Touring models thereafter used the FLT/FLHT frame. Ironically, the FLT Tour Glide, which introduced the current Touring frame, was dropped from the lineup in 1996. The frame-mounted Tour fairing would return with the FLTR Road Glide in 1998.
The Evolution engine was replaced by the Twin Cam 88 engine on all large-frame Harley-Davidson motorcycles in 1999.
The low-compression FL engine was discontinued in 1979, as was the option for hand-shift/foot-clutch transmission controls.