1940 Harley-Davidson EL Knucklehead: Final Pre-FL 61ci OHV Big Twin

The 1940 Harley-Davidson EL occupies a narrow but important place in the Knucklehead story. It was still the original 61 cubic-inch overhead-valve Big Twin concept introduced in 1936, but by 1940 the model had moved beyond the early teething period and into a more mature prewar form. The following year Harley-Davidson introduced the 74 cubic-inch FL, changing the center of gravity of the OHV Big Twin line and making the 1940 EL the last model year before the larger-displacement Knucklehead arrived.

Collectors usually call it a Knucklehead, although that was not the factory name in period. The nickname comes from the distinctive rocker boxes over the overhead-valve cylinder heads, whose rounded contours suggested a clenched fist. For restorers and marque historians, the 1940 EL is not just another prewar Harley; it is the developed 61ci OHV machine immediately before the FL expanded the formula.

Best Known For: the 1940 EL is best known as the final pre-FL 61 cubic-inch Harley-Davidson Knucklehead, combining the original high-compression EL identity with the improved prewar development of Harley’s first production OHV Big Twin.

Quick Facts

The following table gives a concise reference view of the 1940 EL. It avoids figures that are inconsistently documented in period sources and focuses on specifications that matter for identification, restoration, and model comparison.

That summary also explains why the 1940 EL is often researched separately from earlier 1936-1937 machines and from the later FL. It is still the original-displacement Knucklehead, but it belongs to the more developed end of the prewar 61ci line.

Why the 1940 EL Matters

The EL mattered because it was Harley-Davidson’s proof that the American heavyweight motorcycle could move decisively beyond side-valve architecture without abandoning the durability and serviceability expected by police departments, club riders, dealers, and long-distance private owners. The 1936 EL had introduced Harley’s OHV Big Twin idea; by 1940, that idea had become a credible production motorcycle rather than a daring first attempt.

Its importance is sharpened by timing. In 1941 the 74ci FL arrived, giving Harley-Davidson’s OHV Big Twin greater torque and a model identity that would dominate collector discussion. The 1940 EL therefore sits at the end of the pure pre-FL period: a 61ci high-compression Knucklehead before the larger OHV engine changed expectations of what a big Harley could be.

For collectors, that makes the 1940 EL a particularly satisfying machine to study. It has the visual drama of the Knucklehead motor, the leaner character of the 61ci engine, and the prewar civilian stance that later wartime and postwar machines do not quite duplicate.

Historical Context and Development Background

Harley-Davidson entered the late 1930s as one of the dominant American motorcycle manufacturers, but it faced a market defined by hard economic conditions, demanding fleet buyers, and Indian’s continuing strength in the heavyweight class. The company’s side-valve Big Twins were reliable and familiar, yet overhead-valve performance was increasingly attractive to riders who wanted stronger acceleration and higher sustained speeds.

The EL answered that problem in 1936. It retained Harley-Davidson’s 45-degree V-twin layout and Big Twin identity, but replaced the side-valve top end with overhead valves in a new engine that visually and mechanically separated itself from the flathead models. Early production brought oil-control and durability lessons, and Harley made running improvements through the late 1930s.

By 1940 the EL existed in a world just before full wartime production priorities reshaped the American motorcycle industry. Harley-Davidson’s principal U.S. military motorcycle would be the 45 cubic-inch WLA flathead, not the EL Knucklehead. The EL’s significance is therefore primarily civilian, police, and high-performance road use rather than standardized military service.

Racing influence also needs careful handling. The EL was not the same sort of competition tool as Harley-Davidson’s later WR flathead racers or purpose-built Class C machines. Its relevance was road performance: a fast, sophisticated civilian Big Twin whose OHV architecture gave Harley riders a modern alternative to the established side-valve heavyweight.

Engine and Drivetrain

The 1940 EL used Harley-Davidson’s 61 cubic-inch air-cooled overhead-valve V-twin, a 45-degree engine with two valves per cylinder and separate rocker boxes. Those rocker boxes are the source of the Knucklehead nickname and remain the most immediate visual identification feature of the family. Unlike the flathead U and UL models, the EL put its valve gear up in the cylinder heads, giving it a more mechanically exposed and technically modern appearance.

Fuel was supplied through a Linkert carburetor, with exact carburetor details best checked against factory parts books and judging references for a particular machine. Ignition was by battery and coil with a timer/distributor arrangement typical of Harley-Davidson practice of the period. Lubrication was dry-sump, with a separate oil tank and engine-driven oil circulation rather than a simple total-loss system.

The primary drive used a chain to the clutch, and the gearbox was Harley-Davidson’s four-speed Big Twin transmission. Control layout was period-correct rather than modern: hand shift, foot clutch, manual spark control, and separate rider inputs that demand familiarity. The final drive was by rear chain.

Period sources commonly associate the 61ci EL with an output of about 40 horsepower, though restorers should treat any single number carefully because tuning, compression specification, fuel, exhaust, and measurement conventions all matter. What is not in doubt is that the EL was Harley-Davidson’s performance Big Twin before the FL enlarged the overhead-valve idea.

Chassis, Suspension, and Braking

The 1940 EL used a rigid Big Twin frame with a spring fork at the front and no rear suspension beyond the sprung saddle and tire compliance. This layout was conventional American heavyweight practice before telescopic forks and rear suspension became common. It also gives the prewar EL its unmistakable stance: long, low, mechanically open, with the engine visually dominating the center of the motorcycle.

The front suspension was Harley-Davidson’s spring fork, a leading-link design with exposed springs rather than the hydraulic telescopic fork that would define later motorcycles. Braking was by mechanical drums front and rear. Those brakes are adequate only when understood in their period context; they require adjustment, mechanical sympathy, and distance.

The chassis is part of the EL’s appeal and part of its limitation. It has the settled straight-line manners expected of a heavyweight Harley of the period, but it is not a later Hydra-Glide, Duo-Glide, or modern touring motorcycle. A correct restoration should preserve that prewar mechanical honesty rather than disguise it with later convenience parts.

Riding Experience and Mechanical Character

Starting a 1940 EL is a procedure, not a button press. The rider sets fuel and ignition, manages the carburetor, positions the engine with the kick starter, and uses the manual controls with an understanding of mixture and spark. A well-sorted EL rewards that ritual with the dry mechanical clatter and broad V-twin cadence that make early OHV Harleys so different from both flathead predecessors and later hydraulic-lifter machines.

The hand shift and foot clutch define the experience. The clutch is not something a modern rider feathers absent-mindedly at a traffic light; it requires deliberate coordination, particularly on hills or in slow traffic. The gearbox is best shifted with mechanical timing rather than haste, and the rider quickly learns to treat the machine as a system of linked motions rather than a collection of isolated controls.

On period roads the EL’s torque would have felt generous and modern. The 61ci engine does not have the heavier shove of the later 74ci FL, but it is eager for a big prewar American motorcycle and has a cleaner high-performance identity than the side-valve touring twins. The engine pulse is substantial without being crude, and much of the pleasure lies in feeling the OHV motor pull through the hand-selected gears.

The brakes and rigid rear frame keep the experience honest. Speeds that the engine will reach comfortably demand planning when it is time to stop. On broken pavement the saddle and rider absorb what the frame does not, while the spring fork gives the front end a distinct period motion. The EL is stable and commanding, but it is never detached from the road surface.

Identification and Originality

Correct identification begins with the model code. A 1940 EL should be identified by its engine number prefix, with the year and model code stamped on the engine case in the Harley-Davidson practice of the period. Pre-1970 Harley-Davidsons did not use the modern matching frame VIN system, so buyers should not expect a contemporary-style frame number to confirm identity.

The key visual marker is the Knucklehead engine: overhead-valve cylinders, prominent rocker boxes, exposed pushrod tubes, and the compact Big Twin architecture that separates it immediately from the U and UL flathead models. A side-valve Big Twin may share the general prewar Harley silhouette, but the top end is entirely different. The EL’s identity lives in that OHV engine as much as in the tank, fenders, or paint.

Originality is complicated because prewar Harleys were working machines. Police equipment, commercial accessories, later service replacements, postwar upgrades, and decades of custom work can all obscure what a 1940 EL originally carried. Tanks, fenders, forks, wheels, carburetors, lights, saddles, speedometers, and control parts are frequently swapped or reproduced.

Paint and badging require special care. Surviving examples often show restoration-era interpretations, and attractive paint is not the same thing as correct paint. Serious buyers should compare the motorcycle against factory literature, parts books, period photographs, and recognized judging standards rather than relying on a seller’s claim that a finish is “factory correct.”

Engine cases are central to value. A restamped case, mismatched case halves, damaged number boss, altered belly numbers, or non-period replacement components can change a motorcycle’s standing dramatically. A correct 1940 EL restoration is not simply a Knucklehead assembled from good parts; it is a motorcycle whose year-specific identity survives scrutiny.

Model Code and Variant Breakdown

The 1940 EL should be understood within Harley-Davidson’s broader prewar Big Twin lineup. The table below focuses on model codes and closely related machines that collectors commonly compare with the 1940 EL, rather than listing every Harley-Davidson model sold in the period.

Police and commercial ELs are best treated as equipment and order specifications unless documentation proves a particular factory configuration. A siren, special lighting, windshield, or police-style saddle can be period-correct in concept, but those parts alone do not establish original police delivery.

Performance and Dimensional Specifications

The most consistently cited performance figure for the 61ci EL is its period horsepower rating of roughly 40 horsepower. Beyond that, caution is appropriate. Prewar road-test data, gearing, equipment, rider weight, fuel quality, and restoration state all affect speed claims, and hard numbers such as 0-60 mph or quarter-mile times are not consistently documented in a way that should be repeated as fixed specifications.

Weight figures also vary in secondary sources depending on whether a machine is quoted dry, with equipment, or in road trim. For identification and valuation, engine number correctness, model code, major component authenticity, and restoration accuracy matter far more than a single published weight or top-speed claim.

Compared With Related Models

1940 EL vs. Earlier 1936-1937 EL

The earliest ELs are prized as first-year and early-production Knuckleheads, but they also represent the beginning of Harley-Davidson’s OHV learning curve. By 1940 the model benefited from several years of production development and field experience. Collectors who want the earliest historical milestone may chase 1936, while riders and restorers often appreciate the more mature nature of the later prewar machines.

1940 EL vs. 1941 FL

The 1941 FL is the direct comparison everyone makes because it introduced the 74 cubic-inch OHV engine. The FL has the displacement advantage and became the basis for the dominant postwar Big Twin identity. The 1940 EL, however, has the cleaner historical position as the last 61ci-only pre-FL moment, which gives it a particular appeal among collectors who value chronology and mechanical purity.

1940 EL vs. U and UL Flatheads

The U and UL Big Twins were side-valve machines with larger displacement options and strong service reputations. They suit buyers who admire Harley-Davidson’s flathead engineering and heavy-duty utility character. The EL is the machine for those who want the overhead-valve turning point: more mechanically sophisticated, visually more dramatic, and more directly connected to Harley-Davidson’s postwar Big Twin lineage.

1940 EL vs. WLA Military Harley

The WLA is often better known outside specialist circles because of its wartime service and military appearance. It is not a Knucklehead and not a Big Twin EL. The WLA’s 45ci side-valve engine, military equipment, and production purpose place it in a different category entirely, although both machines belong to the same broader Harley-Davidson prewar and wartime historical landscape.

Restoration and Ownership Notes

Restoring a 1940 EL is a serious undertaking because so much value lies in year-correct detail. Knucklehead parts availability is better than it once was, thanks to reproduction components and specialist knowledge, but availability is not the same as authenticity. A motorcycle can be beautifully assembled and still lose historical value if the wrong cases, heads, tanks, fork, lighting, instruments, or controls are used.

The engine demands an experienced builder. Correct oiling, crankshaft work, cam and valve-train geometry, cylinder-head condition, rocker-box sealing, and case integrity are central to reliability. Many Knuckleheads have been modified over decades for performance, touring, chopper use, or simple survival, so a restorer must separate period-correct service history from later improvisation.

Original frame and fork condition should be inspected carefully. Rigid frames can hide repairs, bent sections, altered tabs, sidecar-related stress, or custom-era cutting. A spring fork can look complete while containing worn links, bushings, springs, rockers, or incorrect hardware.

Documentation is especially valuable. Old registrations, dealer paperwork, photographs, club history, police records, judging sheets, and long-term ownership records can all support a motorcycle’s identity. In the absence of documentation, the machine must stand on its physical evidence, and that evidence should be examined by someone who knows prewar Harley-Davidsons specifically.

Buyer and Restoration Inspection Points

A good 1940 EL inspection is not a generic antique-motorcycle walkaround. The following points are the areas that most often separate a desirable, defensible Knucklehead from a costly assembly of mixed parts.

The most expensive mistake is buying a motorcycle because it looks like a Knucklehead without proving that it is a correct 1940 EL. Attractive paint, chrome, and accessories should never outrank engine identity and component correctness.

Collector and Market Relevance

The 1940 EL is desirable because it combines three qualities collectors like: prewar production, Knucklehead architecture, and a precise historical position immediately before the 74ci FL. It is not merely an early Harley-Davidson and not merely an old Big Twin. It is the mature 61ci OHV model at the end of the pre-FL chapter.

Rarity is difficult to discuss responsibly because exact surviving numbers and configuration histories are not consistently documented. What is clear is that genuine, correct, well-documented prewar Knuckleheads are far scarcer than later modified machines, replica builds, and mixed-component restorations. The market tends to reward original cases, correct major parts, documented provenance, and restraint in restoration.

The custom and chopper world also affects the EL’s history. Knuckleheads were prized as hot engines long before they were blue-chip collectibles, and many were stripped, bobbed, raced informally, or rebuilt into postwar customs. That cultural history is real, but for a 1940 EL being evaluated as a collector motorcycle, the same history can mean missing sheet metal, altered frames, non-original tanks, later wheels, and decades of undocumented change.

Cultural Relevance

The Knucklehead gave Harley-Davidson a visual and mechanical language that shaped American motorcycling well beyond its production years. Its exposed pushrod tubes, muscular rocker boxes, and compact V-twin mass became shorthand for the serious American Big Twin. Later Panheads and Shovelheads would carry the lineage forward, but the Knucklehead established the OHV Big Twin grammar.

The 1940 EL belongs to the civilian side of that story. It was the sort of motorcycle that could serve a private owner, a club rider, a police department, or a long-distance traveler before wartime procurement pushed Harley-Davidson’s production toward military 45s. Its importance is less about battlefield imagery and more about the American road: fast highways, club events, dealer service departments, and the emergence of a performance-minded Big Twin culture.

In collector language, “pre-FL EL” is useful because it identifies a specific moment before the 74ci OHV engine reset expectations. That phrase is not factory romance; it is a practical shorthand for a historically meaningful transition.

FAQs

What engine is in the 1940 Harley-Davidson EL Knucklehead?

The 1940 EL uses Harley-Davidson’s 61 cubic-inch air-cooled 45-degree overhead-valve V-twin. It is part of the Knucklehead family, named by enthusiasts for the shape of its rocker boxes.

Why is the 1940 EL called the final pre-FL Knucklehead?

Because 1940 was the last model year before Harley-Davidson introduced the 74 cubic-inch FL in 1941. The EL itself continued as a 61ci OHV model, but the arrival of the FL changed the Big Twin OHV lineup.

How is an EL different from an E model?

Within the 61ci OHV family, the EL is commonly identified as the high-compression version, while E denotes the standard-compression model. Correct identification should be based on engine stamping, components, and documentation rather than appearance alone.

Is a 1940 EL the same as a WLA military Harley?

No. The WLA is a 45 cubic-inch side-valve military motorcycle, while the 1940 EL is a 61 cubic-inch overhead-valve Big Twin civilian model. They are mechanically and historically distinct.

Did the 1940 EL use a hand shift and foot clutch?

Yes. The 1940 EL used the period Harley-Davidson hand-shift and foot-clutch arrangement. That control layout is an important part of both the riding experience and restoration correctness.

What are the biggest originality concerns on a 1940 EL?

Engine cases, number stampings, cylinder heads, rocker boxes, frame condition, fork correctness, tanks, fenders, carburetor, instruments, and controls all require careful verification. Many surviving Knuckleheads contain later service parts or reproduction components.

Is the 1940 EL a good motorcycle to restore?

It can be, but only if the starting point is sound and correctly identified. Specialist knowledge is essential, and the cost difference between a genuine, complete 1940 EL and a mixed-parts project can be substantial.

Collector Takeaway

The 1940 Harley-Davidson EL matters because it captures the Knucklehead before the FL made the OHV Big Twin bigger, heavier in reputation, and more dominant in Harley-Davidson history. It is the last pre-FL expression of the original 61ci idea: a high-compression overhead-valve Harley that had moved beyond the experimental aura of 1936 but had not yet been overshadowed by the 74.

For a collector, that makes a correct 1940 EL a sharply defined prize. It is not the first Knucklehead, not the biggest Knucklehead, and not the wartime Harley everyone recognizes from photographs. Its appeal is more exacting: the developed prewar 61, the high-compression EL code, the hand-shift Big Twin chassis, and the moment just before Harley-Davidson’s OHV future expanded into the FL.