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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteThe Harley-Davidson EL Knucklehead was a 61-cubic-inch overhead-valve Big Twin introduced in 1936 and produced through 1947; the Panhead succeeded it in 1948. “EL” is the motorcycle model designation, while “Knucklehead” is the nickname fans gave its distinctive rocker-cover and pushrod-tube shapes. The machine brought a new engine architecture and styling, but its first-year motorcycles also needed fixes for valve-spring, rocker-lubrication and oil-leak problems.
What is a Harley-Davidson Knucklehead?
The Knucklehead is the name enthusiasts use for Harley-Davidson’s overhead-valve Big Twin engine family made from 1936 through 1947. The first E-model engine kept Harley-Davidson’s familiar 45-degree cylinder angle and displaced 61 cubic inches. A 74-cubic-inch version arrived later. Harley-Davidson describes the engine’s layout as foundational to subsequent air-cooled Harley-Davidson V-Twins. Harley-Davidson’s engine history
The National Motorcycle Museum characterizes the 1936 EL as Harley-Davidson’s first standard-production overhead-valve V-Twin, following earlier side-valve production and limited or smaller overhead-valve applications. The project was more than an engine update: the EL also introduced a new frame and styling. The museum says engineering on a new heavyweight touring design had begun in 1931. National Motorcycle Museum’s 1936 EL feature
Why is it called a Knucklehead?
The nickname describes the visual impression of the rocker covers and pushrod tubes. Harley-Davidson says fans thought the parts looked like a clenched fist, and that fans—not the factory model name—gave the engine its nickname. The manufacturer’s history does not establish when the term first became widespread or identify its earliest recorded use, so a precise coinage date is uncertain. Harley-Davidson’s engine history
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What do EL and FL mean, and how did the models differ?
“E” designated the 61-cubic-inch overhead-valve model introduced in 1936; “EL” refers to the motorcycle. The later 74-cubic-inch version is associated with the FL model line. These designations distinguish models and displacements, not two names for exactly the same machine.
| Model | Displacement and period | Configuration notes |
|---|---|---|
| EL | 61 cubic inches; introduced in 1936 and represented through the Knucklehead’s 1947 final year | The museum says 18-inch wheels were fitted in the first years; 16-inch wheels were typical after full production resumed following World War II. Details varied by year and configuration. National Motorcycle Museum’s 1947 EL feature |
| FL | 74 cubic inches; appeared later | Associated with the larger-displacement version; the cited sources do not provide a complete year-by-year FL specification history. Harley-Davidson’s engine history |
That distinction matters when identifying or restoring a motorcycle: a broad “Knucklehead” label identifies the engine family, but it does not by itself establish the exact model year, displacement or component fitment.
What were the 1936 Knucklehead’s specifications?
The National Motorcycle Museum lists the following for its 1936 EL example. These are museum-reported specifications for that example and year, not a universal specification sheet for every Knucklehead. Its 95 mph top-speed figure is likewise the museum’s listed specification, not a modern independently verified road test. National Motorcycle Museum, 1936 EL feature, published August 7, 2020
| Specification | 1936 EL example |
|---|---|
| Engine displacement | 61 cubic inches (988 cc) |
| Engine configuration | 45-degree overhead-valve V-Twin |
| Bore and stroke | 3.31 inches × 3.50 inches |
| Compression ratio | 7:1 |
| Power | 40 hp |
| Carburetor | 1.25-inch Linkert |
| Transmission and controls | Four-speed hand shift with foot clutch |
| Final drive | Chain |
| Brakes | Front and rear drums |
| Electrical system | Six-volt battery, coil and points |
| Front and rear suspension | Springer fork; rigid rear |
| Weight | 565 pounds |
| Top speed | 95 mph, as listed by the museum |
What problems did the first 1936 Knuckleheads have?
The National Motorcycle Museum reports three main teething problems on early 1936 motorcycles: broken valve springs, poor lubrication at the rocker arms and oil leaks at the top end. According to the museum, Harley-Davidson improved spring metallurgy, redesigned the rockers and sent dealers repair kits for more than 1,000 affected new motorcycles. The museum also notes three successive 1936 “versions” in production records, a reason an early machine’s components may prompt close identification questions. These details are the museum’s account rather than a service-bulletin chronology. National Motorcycle Museum’s 1936 EL feature
The museum reports that more than 1,500 ELs sold in the first model year. That is the museum’s stated figure, not an independently confirmed factory total; the cited sources do not establish complete year-by-year production numbers for the full Knucklehead run. National Motorcycle Museum, 1936 EL feature
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How did the Knucklehead become the Panhead?
Harley-Davidson dates the Panhead era from 1948, immediately after the Knucklehead’s 1936–1947 run. The newer engine brought aluminum cylinder heads, hydraulic valve lifters, improved oiling and crank-pin roller bearings. Harley-Davidson says the Panhead was eight pounds lighter than the Knucklehead. The change was a refinement and successor, while the Knucklehead’s basic architecture remained a template for later air-cooled Harley-Davidson V-Twins. Harley-Davidson’s engine history
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