The Crankcase and accessories


Construction began with the crankcase, a 5" dia solid 6061-T6 round. HUGE amounts of swarf were generated, as the crankcase is more or less a thin-walled shell by the time it was complete. I used a 6" Buck 3-jaw for the roughing work, and a 6-jaw for fine work. The 6-jaw chuck is desireable as it centers better and holds with less pressure, which means less marring. A large 1" dia. boring bar removed the bulk of the swarf. It took roughly 2 weeks to complete. Final indexing work (milling/boring the cylinder flats, and drilling and tapping the cylinder studs), were done on the mill with a dividing head.
The cover was also turned from a large diameter, solid 6061-T6 round. Quite a bit of freehand work was done to achieve the countours you see... no radius tool was used. A single ball bearing is a light press fit in the nose of the cover. The cover will be attached with studs.
With the cover off, the front main bearing and the cam ring are now visible. The cam ring rides in a male radius cut into the front main bearing, which is of SAE 660 bronze. Also visible are the press-fitted tappet bearings, of aluminum bronze. The inside of the cam ring is geared off of a jackshaft/crankshaft assembly, for an 8:1 reduction contrarotating relative to the crankshaft.
This is the jackshaft/cam ring retainer assy. The small, steel spur gear meshes with a gear cut integrally in the crankshaft. The brass spur gear meshes internally with the cam ring... look closely at the above picture, where you can vaguely see the teeth on the inside of the cam ring. The 2 white pads (a third is at 12:00, hidden by a stud) are delrin, and bear against the face of the cam ring to keep it in place.

Faced with tapping over 100 holes in this crankcase was daunting, as aluminum is not fun to tap. I purchased a dozen Sossberg taps, and had at it. I am NOT a clutz with a tap wrench, but I STILL managed to snap one flush with the crankcase I had so laborously created. AAAAARRRRGGH!

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