1958 Harley Davidson FLH Duo-Glide
- Date Published:
- 22 Oct 2019
- Lake Oswego, Oregon
When Harley-Davidson revised its Model F's 74ci overhead- valve v-twin engine in 1948, the new rocker covers gave rise to the unofficial nickname 'Panhead'. This particular line of OHV Harleys had commenced with the introduction of the 61cu in (1,000cc) Model E 'Knucklehead' in 1936, overhead-valve engines having been seen only in singles and racing twins prior to that date. New from the sump plug upwards, the E, and especially the high-compression EL, brought a new level of performance to Harley's roadsters and was immediately well received. Nevertheless, it was not long before H-D was exploring ways of improving its new offering, going down the familiar route, already trodden with the 'flat heads', of increasing engine capacity to 74ci (1,200cc) in the models FS (medium compression) and FL (high compression). Introduced in 1941, the new 'Seventy- Four' incorporated a host of improvements enabling the engine to cope with the increased power, which was now up to 48bhp in the FL's case. By the late 1940s the Knucklehead was beginning to show its age, prompting Harley to engage in a wholesale revision for 1948 in the form of the Panhead. While the engine's bottom end remained fundamentally unchanged, the top end gained aluminium cylinder heads and those distinctive rocker covers. Oil lines were internalised and hydraulic valve lifters adopted, an innovation that greatly reduced tappet noise and simplified maintenance. Maximum power went up to 50bhp in the 74ci FL, but the main advantage of the many improvements was greater reliability. The 'Panhead' featured a new 'wishbone' frame incorporating bowed front downtubes, and in 1949 gained an hydraulically damped telescopic front fork, becoming the 'Hydra-Glide', though this name was originally applied only to the fork and did not become an official model title until 1951/1952. The advent of hydraulically damped rear suspension in 1958 saw the Panhead renamed 'Duo-Glide', while with the addition of an electric starter in 1965 it became the 'Electra Glide'.