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Small Parts
Crank hub
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.
Shaft seal
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 thru. 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 thru in order to keep the
chamber sealed at the bottom. Alternatives: any good rigid insulating
material can be used.
Stock parts
Off-the-shelf parts are not pictured. These include the ball bearings,
nuts, screws, washers, and spacers.
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