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I'm fascinated by Stirling engines and would like to better
understand them. my questions are regarding the small "coffee cup"
style. My questions are 1.Does the power piston have to be a certain
size in relation to the displacer and 2. Is this a totally sealed
system or is there some leakage around the shaft of the displacer
and the power piston and it's cylinder wall? 4. If no leakage is
allowed, what type of seal is used 3. Is the length of stroke of
the "crankshaft" critical or is there a rule of thumb for the
stroke? Thanks to everyone for any information provided.

The MM5 Coffee Cup Engine sold by The Stirling Engine Co. utilizes a diaphragm instead of a piston. Many similar engine use an glass cylinder and graphite piston from and a 4" dia. circle of foam art board 1/4" thick for the displacer in a 4-1/8 x 9/16" high plastic cylinder. The displacer gland is a short brass tube with sliding fit stainless or polished steel rod. These components must be assembled square and concentric. Displacer travel such as to almost but not touch the upper cold plate or lower hot plate. Piston travel ~1/8"

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