NOTE: You can also use a CD for a flywheel. Just mold an
epoxy disk in the center, and drill out an attachment hole.
Now, the moment of truth. Apply heat to the
bottom of the displacer assembly. Does it work?
Try different heat sources: hot tea, coffee, votive
candles, a tin filled with alcohol. Obviously, don’t
melt the plastic displacer ring with too much heat.
Turn the shaft and see what happens. One direction
should be significantly easier than the other; this is
the way your engine runs. After the metal heats for
a bit, your engine will either not run at all, or it will
kind of move but the piston won’t move as high
and low as it could. Or it’ll run perfectly.
If performance is sluggish, make sure all your glue
joints are airtight. Also, make sure nothing is snagging or hanging up. Add oil to the moving parts and
try again. And finally, try making the piston’s cam
shallower. You can also put ice cubes on the cold
plate to increase the temperature differential.
It works! Basically, you’re done, but let’s tune things
up a bit. Check for these problems: friction, hang-ups, overstressed parts (trying to make them do
more than they want to do), and leaks.
Add oil where needed (not much), adjust any
parts causing problems, and keep everything sealed
74 Make: Volume 17
tight. Also, you need to counterbalance the displacer.
First, glue the second crankshaft stand down, and
glue the flywheel to the crankshaft. Get your fan
weights (or pennies) and stick them to various
spots on the wheel (use double-stick tape) until you
find the right spots that offer the best performance
You’re done! Steampunks, start your engines!
How It Works
Start off by pushing the air into the hot side of your
engine, by spinning the flywheel to raise the displacer.
1. The air is heated and expands, raising the
pressure inside the engine and forcing the piston
upward (a stroke).
2. The displacer falls, moving the air to the cold side.
3. The air is cooled and contracts, lowering the
pressure in the engine and sucking the piston back
downward (a stroke).
4. The displacer rises, moving the air back to the
hot side again.
Photography by Jim Shealy
And the cycle repeats. The displacer isn’t really
doing any work, it’s just taking up space to move
the air to one side or the other, so that the heating
and cooling can do the work.