(l'article est en anglais)
The Internet Craftsmanship Museum Presents:
Joe Martin Foundation "Metalworking Craftsman of the Year" award winner for 1997
With the cam cover removed on the 1/8 scale version of the engine, the 4 cam gears can be seen.
If you haven't already done so, read more about Jerry Kieffer, his background and his quest for total scale in his introductory page. There you will also find links to other model engines, tools and clocks he has made.
Harley Davidson "Knucklehead" motorcycles in perfect scale
Jerry Kieffer prefers to work from the real thing when building his scale models. In this case, he actually does own a 1947 Harley Davidson "Knucklehead" motorcycle that he completely restored. That means he can measure each and every part of the real bike to make the scaled down parts for his models. His plan was to model the entire motorcycle and have the motor run and all the systems work. He started with a 1/6 scale model and built the entire engine. It is completed and runs fine, but after thinking more about the project, he felt to model the entire bike at that scale would produce a finished model that would be 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 Harley is now under way and coming along nicely. Photos below will follow the progress as the bike is built piece by piece in complete scale.
One of the ways Jerry challenges himself is to announce beforehand what he intends to accomplish. Sometimes he regrets this later when he runs into seemingly insurmountable problems with a build, but the pressure of coming through with what he has promised causes him to work at a problem until finding a solution rather than simply giving up. In this case he has stated that he wants to be able to start this tiny engine with a kick starter just like the real engine. He also wants the gearbox to function and the speedometer to work. These are some pretty incredible goals when you look at the small size of the bike and think about duplicating all the parts of a transmission or a speedometer and drive in 1/8 scale. Many of the parts are hard enough to make at full size, much less 8 times smaller. Keep in mind that when reducing in size, the part size goes down as a function of the cube root of the volume, not as a simple linear reduction. For example, the volume of a part at 1/2 size is actually 1/2 the length times 1/2 the width times 1/2 the height. That means the 1/2 size version of a 1" cube would be a cube .5 x .5 x .5 or .125 cubic inches—1/8 of a cubic inch. A1/8 size model of a 1 inch cube is .125 x .125 x .125 which equals .00195, or less than 2 thousands of a cubic inch!
Here are photos of some of Jerry's Harley Davidson projects:
The full-size prototype
The first photo shows Jerry's actual restored 1947 Harley Davidson "knucklehead" motorcycle. Jerry's dog poses in the sprung seat. The bike is show quality and isn't ridden because there are zero miles on the NOS speedometer. This bike is being used as the prototype for Jerry's models. Each original part is measured and duplicated in miniature.
The 1/6 scale engine model
Cylinder barrels from a 1/6 scale model of a 1947 Harley Davidson "Knucklehead" motorcycle illustrate some of Jerry Kieffer's talent with metal. This engine is now complete and running. This pair of cylinders was an early version that Jerry later decided needed a slight change, so he made them over. These can be seen on display in the Craftsmanship Museum in Vista, CA.
The model is a 1/6 scale version of the original and actually runs and sounds like a Harley. It was machined from bar stock...no castings were used. The oil pump, sending unit, distributor, generator and regulator are also functional. The cylinders will eventually be painted and the brass areas will be nickel plated like the original. Next to the engine in the photo is a full size air cooled spark plug compared to the 1/6 size spark plugs used in the model. Jerry planed to build a model of the complete motorcycle but felt this engine is too large for that project. Continue below to see progress on the 1/8 scale version he is now making.
The 1/8 scale model in progress
The 1/8 scale engine is coming along nicely. Here it is shown with the pushrod tubes and cam cover in place. The intake manifold and carburetor are also installed.
In the first photo the engine sits next to the frame which has the transmission installed. The second photo is a detail showing the kick starter, internal gears and some of the other transmission parts. A US Quarter in the foreground shows you how small these parts actually are.
The engine and transmission are now installed in the frame. The all metal frame is so perfect that the occasional show spectator will ask Jerry, "Is it made out of plastic?" He simply smiles and say, "No," understanding it was not meant as an insult but is actually a compliment to the quality of work.
The 1/8 scale Harley air cleaner on the right was made by Jerry. He sent it to engraver Roger Ronnie to have the Harley Davison Logo engraved in 1/8 scale. As a practical joke, Roger made the air cleaner on the left, engraved it and gave it to Jerry. Upon close inspection with a jeweler's loop Jerry could see that the tiny letters under the logo said, "Made in China." After Jerry recovered from the surprise, Roger presented him with his actual air cleaner that did say, "Made in USA" like the prototype. Roger's version is on display in the Craftsmanship Museum for your inspection if you can come visit us in Vista, CA. The correct one will be fitted to the engine when it is completed.
A key to this project as far as Jerry is concerned is that he wants the bike to be able to be kick started like the original. This presents a number of engineering challenges because of the small size.
One problem you run into building running engines this small is that not everything can be scaled down. Engine compression is one of those things. If you scale down all the parts of the original kick starter system but keep the compression near that of the original, the tiny parts can't handle the load. These two photos show the primary cover in place and the gear set exposed with the cover off. In the second photo you can see Jerry's solution to how to beef up the kick start mechanism to handle the compression with tiny parts. Behind the gears is a ratchet setup that turns the engine over when the kick starter is pushed, but once the cover is in place, nobody will ever know how it's done.
This is the kind of hidden engineering that separates the real engine modelers from the "instruction followers." Here is how it works: In the first photo the rack gear is not yet engaged with the driving gear. When the kick starter lever is engaged, a spring pulls the rack gear down so it engages the driving ratchet gear (photo 2) that is connected to the primary gear train. As the kick starter moves through its travel to the end (photo 3) it turns the motor over the same number of degrees as the original kick starter did. If the engine fires mid-stroke, the shape of the gears kicks the rack gear out of the way, avoiding an old Harley injury commonly know as "Sportster Knee" where the engine would kick back unexpectedly on the starting lever and either toss the rider over the handlebars or injure his knee. In this case, "Sportster Finger" will be avoided by Jerry's design. He says the sound of the rack feeding back over the ratchet gear even mimics the actual sound of the real kick starter. There is several weeks work involved here just getting the shape of the teeth right between the rack and ratchet gears so it both engages firmly but also kicks out like it should.
The clutch cable was made using a special fixture Jerry designed and turned on a Sherline lathe. The lathe was also used to wrap the wire for the outer cable using this fixture. The inner wire that will actuate the clutch is .010" in diameter and slides freely within the outer cable housing, which is wrapped using .007" wire to an outer cable diameter of .032". It took several tries and weeks of work to design a wrapping fixture that worked, but it works very smoothly.
The wheel spokes are perfect 1/8 replicas of the real spokes. They include a swedged end and a threaded end. The spokes are .020" in diameter and the thread is 190 TPI. The nipple threads onto the spoke for tightening and adjustment as is practice on full-size wire wheels—it is not simply laced with wire as is done on most model wire wheels. Over 100 of these spokes must be produced and eventually individually installed and tightened. The first photo shows the nipple threaded onto the spoke and the second shows it removed so you can see the threads. Jerry expects the wheels, including spokes, rims, valve stems, brakes and bearings to take about 1 year to complete. (2/09)
At the NAMES show in April, 2009 Jerry brought the nearly finished front wheel to display. Note the tiny valve stem. Yes, it does contain a working Shrader valve, and the brass valve cap has the correct number of knurls.
The motorcycle's front forks, handlebars, suspension and headlight are also well along. The throttle cable is installed and works when the throttle is twisted on the handlebars. (4/09)
[more to come... Photos will be added as they become available. Check back now and then to follow the progress of this project. It was slow going while Jerry finished up the Deere tractor project, but now this one is back in full swing again.]
sources : www.craftsmanshipmuseum.com
Photos: Forrest Atkinson