Upper Crankcase Half
Today I worked on the upper crankcase, the crankshaft and its bearings. In the photo below a cut away exposes the detail of the upper crankcase and illustrates how the crankshaft is mounted. The center crankshaft bearing is still missing.
I have highlighted detail of interest in the bottom diagram. The front and rear ball bearings are mounted in aluminum bearing holders (colored green). These are produced on the lathe in a single operation so that all of the features are concentric. The crankcase will be line bored so the mounting points of these crankcase bearing holders and the center bearing will be concentric. I have decided to use metric bearings throughout the engine. The crankshaft big end journals are not centered on the cylinder center axes. By offsetting them as in the real engine, I can get more material at the ends and middle of the crankshaft to make room for larger crank bearing surfaces. In this small model I need as much meat as I can get in the crankcase for the screws that secure the bearings and the two crankcase halves. The real engine has cutouts in the side of the crankcase covered by the crankcase breather covers. Since these will not be seen I will not make these large cutouts, just a single hole for the breather. If I were to put these cutout in, I would lose surface area and screws to secure the two crankcase halves.
Oil will be delivered under pressure to the center bearing through and oil gallery in the crankcase. Internal oil holes in the crankshaft will then deliver oil to the big end journals.
Below is a rear view of the engine showing the rear motor mount and the rear crankcase bearing holder.
Below is the beginning of the crankshaft drawing. I want to drill out the connecting rod crank journals, but the outer most crank web is in the way, I may have to eliminate it as I need these holes to deliver oil to the conrod big ends.
Below is a picture of the 97 cubic inch midget Offy crankcase with the side holes highlighted. I will eliminate these as I will split my crankcase as I have shown in the above pictures.
Next I will turn to the lower crankcase half. I think I will add an oil splash tray in the bottom of the crankcase.