Leticia Cline and Mike Wolfe share their first impressions of the all-new 2024 Harley-Davidson Street Glide motorcycle during their …
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In discussions of classic American culture, Harley-Davidson stands out as an iconic motorcycle brand that has dominated the roads for over a century. Throughout its history, the company has influenced motorcycle trends significantly, introducing comfortable cruisers like the Softail and nurturing motorcycle clubs like the Hell’s Angels. Perhaps more fascinating are its renowned engine designs, including the Panhead, Knucklehead, and Shovelhead. While all share the illustrious Harley name, they each possess unique designs and characteristics, including varied valve cover styles and horsepower ratings.
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Harley-Davidson’s journey began in 1903 with the Model 1, which featured a 24.74 cubic-inch inlet-over-exhaust single-cylinder engine. The lineup continued to evolve with the introduction of the Panhead, Knucklehead, and Shovelhead engines, each representing significant advancements before eventually being phased out. Notably, the engines successively followed each other: the Knucklehead was the first, followed by the Panhead, and then the Shovelhead. Let’s delve into their unique contributions, how they compare, and the reasons for their retirement.
The Knucklehead was Harley-Davidson’s first overhead-valve V-twin engine
After 33 years, Harley-Davidson introduced its first overhead-valve V-twin engine, named the Knucklehead, a nod to its uniquely designed rocker covers resembling knuckles. Before the Knucklehead, the company produced side-valve engines (Flatheads), which, while cheaper to manufacture and maintain, fell short of the power levels boasted by contemporary European bikes. Launched in 1931, the 60.3 cubic inch pushrod-based OHV engine featured a 4-speed constant-mesh transmission and a recirculating oil system.
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Various models of the Knucklehead were released over the years, each showcasing distinct horsepower ratings and engine dimensions. For instance, the 1936 E-model Knucklehead managed 37 horsepower but faced challenges with valve springs that broke easily and significant oil leakage problems. These deficiencies prompted Harley to consider improvements for future iterations. Over the years, the company worked diligently to refine the Knucklehead, addressing its issues, yet ultimately, the successor was already in the works.
The Panhead is shaped like a pan
Following the Knucklehead, Harley-Davidson’s next innovation came from necessity as the post-WW2 landscape demanded motorcycles to cater to an evolving America, which was rapidly improving its road infrastructure. In 1947, the company unveiled the Panhead, designed to manage overheating better by utilizing aluminum in its cylinder heads instead of traditional cast iron. This material choice allowed for greater heat dissipation during high-powered operations. The Panhead featured a revamped oil pump alongside its valves fixed in hard seat rings. Its polished one-piece valve covers earned the engine its “Panhead” moniker.
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Similar to the Knucklehead, power and specifications of the Panhead varied across different models. Earlier iterations ranged from 50 to 55 horsepower, while later versions in the 1960s, which underwent notable updates, reached 60 horsepower. However, despite innovations, the Panhead experienced challenges, particularly concerning the aluminum cylinder heads which expanded more rapidly than their cast-iron counterparts, leading to valve lash and subsequently hampered performance. Although Harley implemented solutions like hydraulic lifters, it was not long before they turned their focus to another significant engine model.
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The Shovelhead was a revival of the big twin engine
Unveiled in 1966, the Shovelhead emerged as an OHV big twin engine, designed to power motorcycles that matched the increasing demand for more robust bikes. Its distinct shape of rocker covers inspired the name “Shovelhead.” Similar to the Panhead, the Shovelhead utilized aluminum cylinder heads, but with enhanced durability compared to earlier models. Harley produced two versions of the Shovelhead, one at 74 cubic inches and the other at 80 cubic inches, both known for their characteristic upturned shovel-like rocker boxes.
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As with previous models, the horsepower varied with the Shovelhead. For instance, early iterations of the 80-cubic-inch model delivered 66 horsepower at 5,600 rpms. While the Shovelhead was aimed at boosting performance and reliability, it still faced challenges like overheating, akin to the Panhead, along with issues such as blown head gaskets and malfunctioning electronic ignition. Problems like these eventually led to the engine’s replacement by the Evolution engine.
The Knucklehead, Panhead, and Shovelhead represent some of the most legendary engines to bear the Harley-Davidson name. Each engine featured its distinct flair, setting it apart not only from its siblings but also marking its individuality against contemporary options available in the market. These innovative engineering feats have significantly impacted the evolution of Harley-Davidson engines as we know them today.
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