6. Cast the piston.
I’ve tried using nearly everything under the sun as
a piston. Nothing worked. Without machining one,
you’re left with few options. So, we’ll cast a piston.
NOTE: For the best piston-casting results, don’t mix the
epoxy in the cylinder. The oil seems to contaminate it
and keeps it from hardening. Mix on wax paper or plastic
wrap. Don’t use 1-minute epoxy; it can shrink too much
or get too hot. Also, don’t use extra-time epoxy; it
probably won’t shrink enough.
7. Make the displacer rod
and 2 lever arms.
6a. Cut 3" of copper pipe; this will be your cylinder.
Deburr the inside edge with a utility knife. Don’t use
sandpaper; you’re smoothing the pipe so you can
push out the cast piston. Clean the inside until it’s
nice and shiny. Window cleaner helps. Here’s a critical step: correctly bending the wire
6b. Wrap the base of the pipe with plastic wrap and rods. Take some more wire and bend a hook in 1 end.
secure with a rubber band. Then oil the inside of the Cut the other end at about 5". This is your displacer
pipe (Figure I, next page). Cooking spray works fine. rod (Figure M). Sand the end and make sure it fits
6c. Pre-warm your 15-minute epoxy components through the hole in the aluminum top plate. Fill the
using a hair dryer. You want it nice and runny. Mix hook with epoxy (Figure N). Go ahead and fill the
enough epoxy to fill ½" of the pipe or so. Fill the piston hook, too.
pipe. Once the epoxy is fully cured, remove the To cut the displacer rod to length, first lay the top
plastic wrap. Your cast piston should push right out plate on top of the bottom displacer assembly that
(Figure J). Before you push it all the way out, mark you glued, so that its small center hole hangs over
the piston and cylinder so you can match them one edge. Put the 5" displacer rod through the holes
exactly later (see tip on page 72). until its hook is resting on the standoff. Mark where
6d. Cut 1" of wire and bend the end into a hook. Drill the rod meets the edge of the bottom plate. Remove
a hole in the center of the piston and glue the hook the rod and cut it where you marked.
in place (Figure K). Now create the 2 lever arm rods. Bend a hook
While you’re waiting for the piston to cure, use J-B onto a length of wire, mark the wire 2" from the base
Weld or J-B Kwik to glue your plastic displacer ring of the hook, then cut it 2½" from the base of the
to the bottom metal plate (Figure L). hook (½" from your mark).