Harley-Davidson Aermacchi short track frame
Harley-Davidson Aermacchi motorcycles are very potent flat track racers you could buy from the Harley-Davidson dealers. They were called CRS (250cc) and ERS (350cc), and had front and rear suspension.
Harley-Davidson also made hard-tail frames as well and included the drawing of the frame in one of the supplement documentation packages sent to dealers. We obtained a copy of that page and made a nice clear scan of ‘Basic Frame Dimension – Short Track Frame, Part #47001-63M’ (see figure 1). The packet actually had 9 pages, and are included at the bottom of this article.
We previously reverse engineered many of the other Harley-Davidson Aermacchi street (SS/H) and racing frames (CRTT/CRS/ERS), so we already had accumulated a substantial amount of data regarding engine mount locations, frame tube sizes and thicknesses, and a “feel” for what the engineers were thinking back-in-the-day. We decided to reverse engineer the hard-tail frame from the simple measurements supplied on the dealer supplement page. Of course, we needed to assume a few things, so we are not guaranteeing this is an exact duplicate of the frame, but it is a good start for someone looking to make a new frame based on this design.
The reader may also want to reference our research on Aermacchi frame tube sizes.
We did notice a small discrepancy with the engine mount positions, see Figure 2. Since we reverse engineered several frames and several engine cases (street 250 and 350cc engines, along with CRS, ERS and CRTT engines) we felt quite confident in our engine mount location data. When we placed a virtual engine in the frame we drew using the dimensions from the manual supplement page, we noticed a slight misalignment, but only by approximately 1mm (0.0254 inch). Where did the misalignment come from? The paper supplements drawing were created with imperial measurements (inches with 2 decimal accuracy), and the Italians designed the engines in metric. We have provided the data for the engine placement in metric, and one can see the measurements are nice round numbers to the nearest mm or at worst 0.5mm. The imperial measurements are a little ugly and are forced to work around motor mounts locations not designed in inches, with numbers like 3.39, 0.98 and 11.41.
The dealer supplement page(s) shows the backbone frame tube bending upwards as it connects to the steering tube. Aermacchi was famous for a backbone that was exactly the opposite and would arch over the engine. We noticed some bikes had the Aermacchi style backbone, along with a picture that is labelled “Matz” that shows the more traditional Aermacchi style and includes the “steering stop” and traditional tank mounting lugs on the steering tube. The Harley-Davidson drawing and the Matz frame picture are very similar, so we are considering making a drawing that resembles the Matz frame by using an Aermacchi SS/H backbone, but making the rake angle 24 degrees (standard Aermacchi street angle is 28 degrees). Like to hear from experts if they know if we can use the standard backbone or if they know of any dimensions related to this related Matz frame so we can more accurately re-create the drawing.
If anyone knows more history on the Harley-Davidson dealer supplement pages or the Matz frame, please give us feedback and we will update the drawings accordingly.
We do hope this helps with frame builders and restorers of Aermacchi and other classic bikes.
If we can help you with any engineering/CAD/scanning, we will give a special price to anyone into old Volkswagens, old motorcycles, and other fun things.
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