Harley-Davidson Knucklehead Motorcycles in Perfect Scale

Jerry's 1/8 scale Harley-Davidson Knucklehead engine.

With the cam cover removed from Jerry’s 1/8 scale version of a Harley-Davidson knucklehead engine, all four cam gears can be seen.

Jerry Kieffer prefers to work from the real thing when building his scale models. In this case, he actually owns a 1947 Harley-Davidson “Knucklehead” motorcycle, which he completely restored. As such, Jerry can measure each and every part of the real bike to make scaled down parts for his models. His goal was to model the entire motorcycle, get the motor to run, and have all other systems working. Jerry started with a 1/6 scale model, and built the entire engine. The miniature motorcycle engine is completed and runs fine. However, after thinking about the project, Jerry realized that modeling at 1/6 scale would produce a finished model too large for his liking.

Rather than continuing on, he left the first engine as a running display model, and started over from scratch in 1/8 scale. The second motorcycle is virtually finished after years of work, and stands as yet another example of Jerry Kieffer’s master craftsmanship. Below, photos of the scale motorcycle projects illustrate the lengthy and complex construction process over the years.

Jerry's first knucklehead engine model, built at 1/6 scale.

Jerry’s first knucklehead engine is a 1/6 scale version of the original, and actually runs and sounds like a Harley. It was machined from bar stock, and no castings were used. The oil pump, sending unit, distributor, generator, and regulator are also functional. The cylinders would eventually be painted, and the brass areas were nickel-plated like the original.

Jerry with his 1/8 scale Harley-Davidson motorcycle.

Jerry displays his tiny 1/8 scale Harley-Davidson motorcycle. This photo was taken at the 2012 NAMES Expo in Detroit, MI. When looking at the detailed close-up photos below, keep in mind how small this model really is! (Photo courtesy of Ken Foran.)

Now, one of the ways that Jerry challenges himself is to announce beforehand what he intends to accomplish. However, those proclamations can be regrettable at times when he runs into seemingly insurmountable problems with a build. Even so, the pressure of following through on his promise motivates him to work at a problem until he finds a solution, rather than simply giving up.

In the case of the scale motorcycle, Jerry stated that he wants to be able to start the tiny engine with a kick starter—just like the real thing. He also wants the gearbox to function, and to have a working speedometer. These are some incredible goals when considering the small scale of the bike. Duplicating all the parts for a transmission, or a speedometer and drive in 1/8 scale is quite a challenge.

Many of the parts are hard enough to make at full-size, let alone 8 times smaller. Keep in mind that when reducing in scale, the part size gets smaller as a function of the cube root of the volume. It is not a simple linear reduction. For example, the volume of a part at 1/2 scale is actually 1/2 length X 1/2 width X 1/2 height. That means that the 1/2 scale version of a 1” cube would be .125 cubic inches—or 1/8 of a cubic inch. A 1/8 scale model of a 1” cube is .125 X .125 X .125, which equals .00195—less than 2 thousandths of a cubic inch!

1/6 Scale Harley-Davidson Knucklehead Engine Model

1/8 Scale Harley-Davidson Knucklehead Motorcycle

The following photos show Jerry’s progression on the 1/8 scale Knucklehead. 

Knucklehead Speedometer and Air Cleaner 

Jerry’s scale Knucklehead has a working speedometer that’s about 1/2” in diameter. Jerry submitted a video of the speedometer in action. The short video shows Jerry spinning the speedometer shaft to get the needle to move. He noted that, like the full-size speedo, the needle bounces around a bit in the lower speed ranges. However, it smooths out as the speed tops out at about 40-50 mph. Just getting the tiny magnets properly placed in this little gem took several months of adjustment. The work was worth it though, because one of Jerry’s main goals for this project was to have a functioning speedometer—along with a kick starter, working brakes, transmission, and pressurized tires.

The 1/8 scale Speedometer for the Knucklehead.

The functional 1/8 scale Speedometer for the Knucklehead. This tiny working mechanism is smaller than Jerry’s thumb.

The photo below shows two scale air cleaners for Jerry’s Knucklehead motorcycle. The 1/8 scale Harley-Davidson air cleaner on the right was made by Jerry. He sent it to master engraver Roger Ronnie to have him engrave the logo at 1/8 scale. As a practical joke, Roger made a replica air cleaner of his own (on the left), and gave it to Jerry. Upon closer inspection, Jerry could see that the tiny letters under the logo read, “Made in China.” After Jerry recovered from the surprise, Roger presented him with his actual air cleaner with the original engraving: “Made in the USA.” Roger’s version of the tiny air cleaner is on display in the Craftsmanship Museum, while the correct one has been fitted to the engine.

Two scale model Knucklehead air cleaners.

This section is sponsored by:

Sherline Products

Makers of precision miniature machine tools and accessories. Sherline tools are made in the USA.


Sherline is proud to confirm that Jerry Kieffer uses Sherline tools in the production of his small projects.

Artisan added: December 27, 2021 - Last modified: October 23, 2023

Presented by The Joe Martin Foundation for Exceptional Craftsmanship