Sketch of a Harley-Davidson concept component

MENOMONEE FALLS, Wisc.--The Harley-Davidson Steel Toe Tour at the company's Powertrain Operations plant here gives visitors a behind-the-scenes look at the engine-build process, as well as some insight into how a bike evolves from a sketch on a notepad to a roaring machine on the open road.

In 2010, Harley-Davidson, the last American motorcycle manufacturer, started giving tours at the company's primary engine manufacturing plant here just north of Milwaukee. Only about 2,000 motorcycle enthusiasts have taken the Harley-Davidson Steel Toe Tour, and CNET got to tag along for it this weekend.

While portions of Harley-Davidson's operation are off limits to photographers, we were allowed to offer some images from the company's factory and museum archives. This rare sketch of possible passenger seat designs for the Harley-Davidson Rocker concept bike shows that the entire process all starts with pen, ink, and paper.

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Harley-Davidson V-Twin blueprints

The Harley-Davidson Powertrain Operations Plant is the home of the company's signature V-Twin engine, which is detailed in these complex blueprints. The completed engines are sent to bike assembly plants in Pennsylvania and Missouri. (We got a tour of the York, Pa., plant last summer.)
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Harley Davidson V-Twin schematics

These intricate design schematics show an early, internal view of the Harley-Davidson engines built at the Powertrain Operations facility outside Milwaukee.
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Harley-Davidson test parts

Before being cast or assembled into Harley-Davidson engines, parts are created in resin, clear plastic, or other materials to test their construction and function.
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Harley-Davidson V-Rod clay mockup

Before a bike is built into a concept and fitted with an engine, the company's designers and artists model its frame by hand out of clay, as seen with this V-Rod mockup model.
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The Harley-Davidson XR1200 styling mockup

The Harley-Davidson V-Twin engine sits in the middle of this XR1200 mockup to demonstrate how engineers build test constructions to study engine placement and styling.
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The Harley-Davidson VSRC V-Rod Muscle final construction

After clay modeling and styling mock-ups, final custom construction with all working parts--including the functioning V-Twin--went into this Harley-Davidson VSRC V-Rod Muscle.
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Harley-Davidson computer analysis unit

Once a new design is constructed and the motorcycle is fully equipped, components are wired into a computerized data-gathering test unit that analyzes multiple aspects of the bike's performance.
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Robots do the touchy work at Harley-Davidson

Who does the actual building? About 100 human workers operate during two daily shifts at the Harley-Davidson Powertrain Operations plant, but Swedish-made robots like this one do assembly, welding, and inspection work on the company's assembly line.
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Styling and finish options on Harley-Davidson parts

Engine components and other Harley-Davidson parts used at the Powertrain Operations facility can be treated and modified with chrome, black matte, graphite, and other styling options.
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