1939 Harley-Davidson EL Knucklehead: The 61ci Prewar OHV Big Twin

The 1939 Harley-Davidson EL sits at a particularly important point in the first generation of Milwaukee overhead-valve Big Twins. It was not the first Knucklehead, and it was not yet the larger 74 cubic inch FL that would arrive for 1941, but it represents the 61 cubic inch OHV concept after the rushed and troublesome 1936 debut had been refined into a more dependable road motorcycle. For collectors, that makes the 1939 EL a highly desirable prewar civilian Knucklehead: mechanically advanced for its day, visually pure, and close enough to the original 1936 design to retain the early character without carrying quite the same development burden.

Best Known For: the 1939 EL is best known as the high-compression 61ci prewar Knucklehead, a civilian Harley-Davidson Big Twin that helped establish the overhead-valve V-twin as the company’s performance identity.

Quick Facts

The EL was the higher-compression version of Harley-Davidson’s 61 cubic inch E-series overhead-valve Big Twin. The following table summarizes the details most useful to historians, restorers, and buyers evaluating a claimed 1939 EL.

The word Knucklehead was not a factory model name in the period sense. It is the enthusiast nickname for the 1936-1947 Harley-Davidson OHV Big Twin engine, derived from the shape of its rocker boxes. In the collector market, however, the nickname is unavoidable: a 1939 EL will almost always be discussed as a prewar Knucklehead, and the EL code matters because it distinguishes the higher-compression 61 from related E-series machines.

Why the 1939 EL Matters

The 1939 EL deserves its own place in Harley-Davidson history because it shows the Knucklehead after its painful birth but before wartime priorities and the larger FL reshaped the Big Twin line. The 1936 EL introduced Harley’s production overhead-valve Big Twin under immense pressure, and early examples acquired a reputation for oiling and containment troubles. By 1939, factory development had moved the motorcycle closer to the durable, fast, long-legged machine Harley had intended.

This matters because Harley-Davidson’s OHV Big Twin was not merely a styling exercise or a racing-derived curiosity. It was a strategic answer to riders who wanted more speed, more sustained road performance, and a modern mechanical statement against Indian and the remaining American competition. The 1939 EL is one of the clearest prewar expressions of that answer: compact 61ci displacement, four-speed gearing, hand-shift controls, rigid chassis, and the exposed mechanical architecture that later made the Knucklehead central to bobber and chopper culture.

Historical Context and Development Background

Harley-Davidson entered the late 1930s still dealing with the economic aftermath of the Depression. The company had survived where many American motorcycle builders had not, but survival did not remove the need for new engineering. The side-valve VL Big Twin had carried the brand through the early part of the decade, yet the market was changing. Riders, police departments, and sporting customers increasingly expected higher sustained speeds and better top-end performance.

The EL arrived in 1936 as Harley-Davidson’s first production overhead-valve Big Twin. Its four-cam lower end followed established Milwaukee practice, but the new cylinder heads, rocker gear, recirculating dry-sump oiling, and higher operating demands made it a much more ambitious motorcycle than the flathead models surrounding it. The first-year EL gained fame and notoriety in almost equal measure: fast, handsome, and advanced, but also subject to the sort of teething problems expected from a major new design released under commercial pressure.

By 1939, the E-series had become a more credible long-distance machine. The motorcycle still retained the visceral prewar layout: spring fork, rigid rear frame, foot clutch, tank shift, external oil tank, and a visibly mechanical engine. Yet it represented a clear step away from the low-revving flathead world. That dual identity is a central part of the 1939 EL’s appeal. It is modern enough to be a true performance Harley of its era, but old enough to preserve the rituals and mechanical exposure of the prewar American road motorcycle.

The competitor landscape was led chiefly by Indian, especially the Chief and Sport Scout lines. Indian continued to develop strong side-valve motorcycles with excellent road manners, while Harley pursued the overhead-valve route for its sporting Big Twin. The Knucklehead did not make every flathead obsolete overnight, but it gave Harley-Davidson a new engineering identity that would run through the Panhead, Shovelhead, Evolution, and later Big Twin lineage.

Engine and Drivetrain

The 1939 EL used Harley-Davidson’s 61 cubic inch, 45-degree overhead-valve V-twin. The engine’s most recognizable feature is the pair of cast rocker boxes, whose rounded, lobed form gave rise to the Knucklehead nickname. Beneath that visual signature sat a dry-sump engine with external oil tank, gear-driven camshafts, pushrods, and two valves per cylinder.

The EL suffix identified the higher-compression version of the 61ci E-series engine. Period and later reference sources commonly list the EL at about 40 horsepower, though restorers should remember that real output depended heavily on tune, compression parts, carburetion, ignition condition, exhaust, and the standards by which the figure was recorded. The model’s reputation was not built on a modern peak-output number; it was built on the way the OHV engine pulled through taller road speeds than the older flathead Big Twins.

Fuel was supplied by a Linkert carburetor, with the exact carburetor specification an important restoration detail to confirm against parts books and factory literature for the machine in question. Ignition was battery-and-coil rather than a magneto competition arrangement. The primary drive used chain drive to a multi-disc clutch, feeding a four-speed gearbox operated by a hand lever through a gated shift arrangement. Final drive was by chain.

The following specifications are the core mechanical facts most often needed when evaluating a 1939 EL engine and drivetrain.

The technical importance of the EL is not simply that the valves moved upstairs. Harley-Davidson had to make an OHV Big Twin that ordinary owners could kick-start, ride through poor fuel, service with familiar tools, and operate over long distances. The 1939 model year falls in the period when that concept had become much more convincing.

Chassis, Suspension, and Braking

The 1939 EL retained the traditional American Big Twin chassis formula: a rigid rear frame, a sprung front fork, large fuel tanks, substantial fenders, and a riding position meant for real road mileage. This was not a lightweight sporting single or a stripped competition machine. It was a fast road motorcycle built around the touring and utility expectations of American buyers.

The rigid frame gave the motorcycle a direct, mechanical feel but placed great importance on saddle springs, tire volume, and road surface. The Harley spring fork was durable and familiar to mechanics of the period, though it did not offer the damping or wheel control that telescopic forks would later provide. Drum brakes front and rear were adequate by late-1930s standards when correctly set up, but they demand an entirely different braking strategy from a modern rider.

The following chassis table focuses on documented layout rather than speculative dimensions.

Visually, the 1939 EL has the stance collectors associate with the best prewar civilian Harley-Davidsons: long tanks, exposed pushrod tubes, the compact but muscular OHV top end, valanced fenders depending on equipment, and a machine-like density around the engine and gearbox. It is not as bare as an early board-track machine and not as massive as a postwar dresser. Its appeal lies in that narrow band between industrial purpose and American streamlining.

Riding Experience and Mechanical Character

A correctly set-up 1939 EL begins with ritual. Fuel and ignition are not hidden behind a starter button; the rider manages choke, spark advance, throttle opening, and a committed kick. A good EL should not feel delicate, but it does ask for mechanical sympathy. The starting procedure is part of the machine’s personality, especially when cold oil, Linkert carburetion, and foot-clutch habits are all in play.

Once running, the engine has a sharper mechanical note than a flathead Big Twin. The valve gear adds a purposeful top-end sound, while the 45-degree firing intervals give the familiar Harley pulse without the rubber isolation and mass damping of later eras. The EL’s torque is broad rather than frantic, but the overhead-valve breathing gives it a cleaner willingness to pull at road speed than the side-valve models it effectively superseded for performance buyers.

The hand-shift, foot-clutch layout defines the ride as much as the engine does. Smooth departures require coordination, especially in traffic or on grades. The gearbox rewards a deliberate hand and a sense of engine speed rather than hurried modern shifting. Once settled into top gear, the EL feels like what it was meant to be: a fast American road motorcycle, comfortable covering ground on the roads of the late 1930s if the rider accepts the braking distances and surface harshness of a rigid rear end.

Braking performance is modest by any modern comparison. The drums can work well when round, properly lined, and correctly adjusted, but the rider plans stops rather than relying on last-second force. Stability is generally a strength at speed, while low-speed handling requires respect for weight, steering lock, foot-clutch technique, and the realities of a rigid chassis on uneven pavement.

Identification and Originality

Identification is one of the central issues with any prewar Knucklehead. These motorcycles were used hard, modified early, customized after the war, and restored through decades when exact factory detail was not always the priority. A claimed 1939 EL should be assessed as a whole motorcycle, not merely as an engine number attached to attractive paint.

The engine number is the key legal and collector identity point on a 1939 Harley-Davidson Big Twin. A genuine EL engine number should carry the appropriate 1939 EL model prefix followed by its serial sequence. Harley-Davidson frames of this period did not carry the later-style matching frame VIN used in subsequent decades, so collectors examine engine-number stamping style, case integrity, belly numbers, casting details, and the compatibility of major chassis components rather than looking for modern matching frame and engine numbers.

Correctness extends well beyond the number pad. Important areas include rocker boxes, heads, crankcases, cylinders, cam cover, oil pump, carburetor, timer, tanks, dash, speedometer, fork, hubs, brakes, fenders, toolbox, battery box, exhaust, and primary covers. Reproduction parts are widely used in Knucklehead restoration, and many are useful, but a motorcycle with original major castings and sheet metal is viewed differently from one assembled largely from new parts around a set of cases.

Collectors should be especially wary of postwar updates presented as original 1939 equipment. Later tanks, later forks, altered fenders, replacement transmissions, incorrect carburetion, welded or raked frames, and bobber-era trimming are common. Some modified machines have genuine period hot-rod or club history and deserve preservation on those terms, but they are not the same proposition as an accurately restored civilian 1939 EL.

Paint and trim require careful documentation. Factory paint options and striping details should be verified through period literature, reliable marque references, and surviving original-paint examples. Fresh paint can make an incorrect motorcycle look convincing, while old paint can conceal serious mechanical substitution. On a prewar EL, provenance, photographs before restoration, invoices from recognized specialists, and a coherent parts trail carry real weight.

Model Code and Variant Breakdown

The 1939 EL belongs to the E-series 61ci Knucklehead line. Harley-Davidson model codes are central to understanding what a motorcycle was when new, but police, commercial, and export equipment could be fitted without always creating a fundamentally separate engine family. The table below keeps to the model relationships most relevant to a 1939 EL buyer or restorer.

The absence of a glamorous factory racing suffix should not diminish the EL’s importance. Its significance lies in being the road-going OHV Big Twin that set the mechanical vocabulary later Harley performance machines inherited.

Performance and Dimensional Specifications

Period sources and later references commonly describe the EL as producing about 40 horsepower in high-compression form. That figure should be treated as a period reference point, not a modern chassis-dynamometer guarantee. Compression specification, fuel quality, carburetor condition, ignition timing, exhaust restriction, and engine wear all make a large difference in how a restored EL performs.

Reliable period top-speed, acceleration, weight, and dimensional figures are not consistently presented across sources in a way that should be repeated without qualification. What is historically secure is the role the motorcycle played: it was Harley-Davidson’s sporting OHV 61ci Big Twin, appreciably more advanced in breathing and road-speed potential than the older side-valve Big Twins. In collector and restoration work, mechanical authenticity matters more than quoting unsupported performance numbers.

Compared With Related Models

1939 EL vs. E

The closest comparison is the standard E. Both are 61ci overhead-valve Knuckleheads, but the EL denotes the higher-compression specification. For collectors, that single letter is meaningful because it identifies the more sporting version of the 61ci Big Twin. Authentication should focus on the engine number, original configuration, and whether the machine has been rebuilt with parts that blur the distinction.

1939 EL vs. 1936 EL

The 1936 EL carries first-year importance and a special place in Harley-Davidson history, but it also belongs to the earliest development phase of the Knucklehead. The 1939 EL is often attractive to riders and restorers because it retains prewar character while benefiting from several years of factory refinement. First-year cachet and mature usability are different kinds of desirability.

1939 EL vs. 1941 FL

The 1941 FL introduced the 74 cubic inch Knucklehead and changed the Big Twin conversation. The FL offers larger displacement and has enormous collector demand, but it is not the same motorcycle historically. The 1939 EL belongs to the original 61ci prewar OHV line, before the 74 became the dominant postwar enthusiast reference point.

1939 EL vs. WL and WLA Flatheads

The WL and military WLA flatheads are smaller side-valve 45 cubic inch machines, very different in purpose and performance. They are often encountered by new collectors because of wartime production and parts availability, but they do not substitute for an EL. The Knucklehead is a Big Twin OHV motorcycle with a different chassis presence, valuation structure, and restoration challenge.

Restoration and Ownership Notes

Restoring a 1939 EL is a serious undertaking even though specialist knowledge and reproduction support are far better than they once were. Engine work should be entrusted to builders who understand early Knucklehead oiling, case repair, line boring, flywheel assembly, valve-train geometry, rocker-box sealing, and the cumulative effects of mismatched reproduction and original parts. These engines can be reliable when built correctly, but they are unforgiving of casual assembly.

Crankcases are the heart of the motorcycle’s identity and value. Repairs around the number boss, broken mounts, welds, mismatched case halves, damaged cam areas, and incorrect machining all affect both mechanical integrity and collector confidence. A shiny restoration with suspect cases is a very different purchase from an older, less cosmetically perfect motorcycle with strong original foundations.

Sheet metal is another major cost driver. Original tanks, fenders, oil tanks, toolboxes, and dash components can be difficult and expensive to source. Reproduction sheet metal can be appropriate for a rider-grade build, but the best collector restorations are judged by the authenticity and condition of original major components as much as by paint quality.

Ownership also requires familiarity with period controls. A foot clutch and hand shift are not obstacles for an experienced antique rider, but they demand practice and mechanical adjustment. A 1939 EL should be maintained as a prewar machine: regular oil checks, careful ignition and carburetor tuning, chain attention, brake adjustment, and respect for heat, oil leaks, and vibration.

Buyer and Restoration Inspection Points

The strongest 1939 EL purchases are not always the prettiest motorcycles. They are the machines with coherent identity, correct major castings, uncut chassis parts, documented restoration work, and a believable history. The following inspection points reflect the areas that most often separate a valuable prewar Knucklehead from an expensive parts puzzle.

A good inspection should be slow and unsentimental. Prewar Knucklehead values reward correctness, but the motorcycle’s desirability has also encouraged restamped cases, assembled machines, and restorations that look convincing from ten feet away. Serious buyers should use marque specialists before committing to a major purchase.

Collector and Market Relevance

The 1939 EL sits in a prized corner of the Harley-Davidson collector market: prewar, overhead-valve, Big Twin, and recognizably Knucklehead. Those four descriptors carry more weight than cosmetic glamour alone. Collectors typically value original crankcases, correct 1939 EL identity, original sheet metal, uncut frames, accurate mechanical equipment, and documented restoration by known specialists.

Rarity is not always easy to express through a single production figure because exact model-specific counts are not consistently documented in all sources, and surviving examples vary dramatically in authenticity. What can be said with confidence is that unmolested prewar ELs are far scarcer than restored or modified motorcycles wearing Knucklehead identity. Decades of bobber building, chopper conversion, police service, civilian utility, and hard riding consumed many original parts.

Auction interest in Knuckleheads has long favored first-year 1936 machines, highly original prewar examples, correct paint restorations, and documented special-service motorcycles. The 1939 EL has a slightly different appeal: it is a mature prewar 61, not a first-year gamble and not a later 74. That makes it especially attractive to collectors who want the early OHV experience in a form that feels historically complete rather than merely famous.

Cultural Relevance

The Knucklehead’s cultural importance did not end with its factory production run. After the war, surplus parts, returning servicemen, club riders, and mechanically inventive owners helped create the bobber idiom that later fed directly into chopper culture. The EL was one of the engines riders wanted because it looked right, ran hard, and carried the prestige of the overhead-valve Big Twin.

Police and commercial users also gave the E-series practical legitimacy. Harley-Davidson Big Twins were working motorcycles as much as enthusiast machines, and the EL’s speed and durability made it attractive where performance mattered. A police-equipped or service-documented example should be evaluated carefully, as genuine equipment and paperwork can add historical interest, while later accessory additions should not be mistaken for provenance.

In racing terms, the 1939 EL was not a cataloged factory racing model in the way a dedicated competition machine would be. Its influence was broader: it established the OHV Big Twin as the engine architecture serious Harley riders associated with power. That association outlived the Knucklehead itself and shaped the way later generations judged Panheads, Shovelheads, and custom Harley performance builds.

FAQs About the 1939 Harley-Davidson EL Knucklehead

What engine is in the 1939 Harley-Davidson EL?

The 1939 EL uses a 61 cubic inch, approximately 989 cc, 45-degree overhead-valve V-twin. It is part of the first-generation Harley-Davidson Knucklehead family, with pushrod-operated overhead valves and distinctive rocker boxes that gave the engine its nickname.

What does EL mean on a 1939 Harley-Davidson?

In this context, EL identifies the higher-compression version of Harley-Davidson’s 61ci E-series overhead-valve Big Twin. The standard E was the related lower-compression 61ci model, while the later FL code refers to the 74ci Knucklehead introduced for 1941.

How do you identify a real 1939 EL Knucklehead?

The key starting point is the engine number, which should have the correct 1939 EL prefix and credible factory-style stamping. Because Harley-Davidson frames of this period did not use later matching frame VIN practice, collectors also examine crankcase integrity, case matching, correct engine castings, chassis compatibility, sheet metal, fork, dash, carburetor, and documentation.

Is the 1939 EL a prewar Knucklehead?

Yes. The 1939 EL is a prewar 61ci Knucklehead. In collector language, prewar usually refers to civilian machines built before wartime production and military priorities changed the motorcycle market and Harley-Davidson’s manufacturing focus.

How much horsepower did the 1939 EL make?

The high-compression EL is commonly listed at approximately 40 horsepower in period and standard reference contexts. That figure should be understood as a factory-era rating rather than a guaranteed output for any surviving motorcycle, since tune, wear, compression parts, carburetion, ignition, and exhaust condition all matter.

Are parts available for a 1939 EL restoration?

Specialist support and reproduction parts are available, but that does not make a correct restoration easy. Original crankcases, heads, rocker boxes, sheet metal, forks, hubs, dash components, and small fittings remain critical. A restoration using many reproduction parts may be rideable and attractive, but it will be judged differently from a motorcycle retaining major original 1939 components.

Why is the 1939 EL valuable to collectors?

It combines prewar production, 61ci OHV engineering, high-compression EL specification, and Knucklehead visual identity. Collectors value it because it represents Harley-Davidson’s early overhead-valve Big Twin after several years of refinement, while still retaining the hand-shift, rigid-frame, spring-fork character of the late 1930s.

Collector Takeaway

The 1939 Harley-Davidson EL is one of the most satisfying prewar Knuckleheads to understand because it is not dependent on first-year novelty or later 74ci displacement to make its case. Its importance is more disciplined than that. It is the 61ci overhead-valve Big Twin after Harley-Davidson had begun turning the ambitious 1936 idea into a credible road motorcycle.

For the collector, the best 1939 EL is a machine with honest identity: correct cases, coherent components, uncut chassis, proper mechanical detail, and documentation that survives close inspection. For the rider, it offers the concentrated experience of a prewar American performance motorcycle: foot clutch, hand shift, spring fork, rigid rear, Linkert breathing, and that unmistakable OHV top end working in the open air.

The EL matters because it is the hinge between old Harley and modern Harley. It still belongs to the world of exposed mechanisms and rider-managed controls, yet its engine points straight toward the Big Twin future. A correct 1939 EL is not merely a collectible Knucklehead; it is one of the clearest surviving statements of Harley-Davidson’s decision to make overhead-valve performance central to its identity.