The Excelsior Project, 1: Engine Casing
The OHC Excelsior racer is based on a set of 1919 cases, modified to have a bevel drive for the cams and magneto. Below are stock 1919 cases. Note how the bottoms are quite corroded, probably from sitting in the ground for many years. Perfect cases for the prototype...
Here the right case has been setup in the mill, and the stock timing chest removed. This was a fun job, not too fussy!
Fixing the corrosion. Aluminum tubes were machined up, cutaway to match the cases, then glued in place. Bondo is used to fill the gaps and corrosion. I have to get the outside shape of the engine first, then I can figure out how everything fits inside. I think it's called "reverse engineering".
This is the basic shape of the bevel drive. The case is sitting on a full size drawing of the engine. This worked OK for the first mockup of the bevel drive, but when I drew the engine in Autocad, the shape changed a little. I was learning positions of shafts and gears as the engine started to reveal itself...
The cylinders on this racer are larger than the stock cylinders. The fin spacing is different too. I decided to machine a couple from solid 6061 aluminum. Here is the start of the process. I don't need a hole right through, they just have to look correct on the outside.