This is my version of Jerry Howell's design for a water-cooled Ringbom
Stirling engine.  In the Ringbom design the displacer, housed in the
vertical brass cylinder is entirely free - it has no mechanical
connection to the driveshaft.  The displacer is driven up and down by
the changing pressure inside the engine.

The brass cylinder is a water jacket.  The small pump on the top of the
engine, driven by a belt from the crankshaft, pumps cooling water into
the base of the jacket, forcing warm water out the top and back to the
plastic reservoir seen in the background.

Graphite is used extensively in the engine because of self-lubricating
properties.  The power piston is graphite as is the cylinder in the
water pump.  In addition, the displacer slides up and down in a graphite
bushing.

The engine is a good runner and a sure-fire attention getter.