At your mark, bend a 90° angle, then bend a bit
of the end as well (to keep the piston and displacer
rod hooks from sliding off). Make another rod in the
same fashion (Figure O).
Fill the hooks on the lever rods with epoxy as you
did on the previous 2 hooks.
8. Mount the piston cylinder.
Again, clean the inside of your copper cylinder very
well. Center it over the large hole you drilled on the
top plate and epoxy it in place (Figure P).
Once cured, wipe the inside of the pipe with an
oiled towel. Test the piston in it. Align the marks on
the piston and cylinder, then move the piston up
and down until it travels freely in the cylinder.
TIP: The inside of a copper pipe is extruded, meaning it
has small ridges that run its length. These need to be
matched with your piston, which was cast with these
ridges as well. Just move the piston up and down, slowly
twisting until it moves freely.
Make: Volume 17
9. Bend the crankshaft.
The crankshaft is probably the most critical part of
your engine. It must be as straight as possible, and
its 2 cams must not be too deep. Its piston cam
must be 0.15"–0.20" deep, and its displacer cam
must be a little less than 0.25" deep.
Also, the cams need to be 90° out of phase from
each other: if one is lying flat on the workbench, the
other should be standing straight up. You probably
won’t get it right the first time, so don’t sweat it.
Measure the distance between the piston rod and
displacer rod (Figure Q) and mark their locations on
a sheet of paper; these indicate where the cams will
go (Figure R).
Cut an 8" length of rod. Bend the first cam, using
both sets of pliers to hold and shape the wire. Bend
the second cam offset 90° from the first. Make sure
the wire still lies flat and the cams are where you
want them after bending. Roll the wire to make
sure it’s still straight, and straighten it if necessary.
Photography by Jim Shealy (L, P, Q) and Ed Troxell
NOTE: The cams can be bent in trapezoidal shapes
rather than rectangles.