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The crank hub connects the crank shaft to the connecting rod. The hub is made of 1/4" 6061 aluminum. The slots allow the hub to clamp to the crank shaft via a #4 bolt thru the two small holes. The slots also provide a mount for the bearing, allowing the piston stroke to be adjusted. The two large holes help balance the hub. Washers on the #4 bolt fine tune balance. Alternatives: A simple disk with a hole for the crankshaft, a hole or two for a bearing post, and a set screw was used in an earlier design. Although it was acceptable it tended to wobble slightly and did not provide a way to balance the weight of the bearing.
Shaft seal housing
The brass shaft seal housing, shown upside down, retains the top shaft bearing and the shaft seal. The housing press fits to the top center insulator. The hidden end is simply a continuation of the visible round hole. Alternatives: aluminum should work acceptably.
The shaft seal, shown upside down, is composed of three parts – a brass cap, a short piece of latex tubing, and a graphite bushing (recently changed to brass).
The assembly lightly press fits into the shaft seal housing. The latex allows the graphite bushing to adapt to any wobble in the crankshaft. The graphite bushing is a small cylinder of graphite with a small hole for slip fit to the crankshaft. The graphite provides a nearly air-tight seal with low friction.
Crank bearing & crank ring
The crank bearing attaches the connecting rod to the hub. The brass crank ring provides a groove that secures the connecting rod to the bearing. The crank ring is C shaped and presses onto the bearing. Alternatives: the ring can be omitted and the connecting rod glued to the bearing.
Top center insulator
The top center insulator provides a mount for the seal housing while minimizing heat flow between the hot and cold plates. The material is acrylic or abs. The hole goes fully through. Alternatives: any good rigid insulating material can be used.
Bottom center insulator
The bottom insulator provides a mount for the lower bearing while minimizing heat flow between the hot and cold plates. The material is acrylic or abs. The hole does not go fully through in order to keep the chamber sealed at the bottom. Alternatives: any good rigid insulating material can be used.
Off-the-shelf parts are not pictured. These include the ball bearings, nuts, screws, washers, and spacers.