10. Glue up the displacer
and the crankshaft.
Drill a r" hole (or one size bigger than your wire)
in the center of each epoxied rod hook. Put the
displacer rod through the standoff and center hole
again. Drill (or poke) the rod into the exact center
of the foam board displacer disks and epoxy it in
place (Figure S). Make sure it’s attached really well.
It’s a royal pain if it falls off after you’ve glued the
displacer assembly together. Now glue the top plate
onto the displacer ring. I suggest using hot glue.
(Don’t use hot glue on the bottom plate, as it will
melt during operation of the engine.)
Cut a 5" length of PVC pipe, then cut it in half
lengthwise (Figure T). These pieces become our
crankshaft stands to hold the crankshaft and flywheel in place. Measure how high the shaft will need
to be — so that when the displacer rod is raised
halfway, the lever rod hole is level with the shaft
— and drill a hole in each stand at that height. I’d
suggest drilling holes just above and below this one,
just in case the height of the crankshaft needs to be
adjusted during engine tuning.
Finally, epoxy one crankshaft stand right behind
the piston cylinder, lined up with the piston and
displacer rods. Don’t glue the opposite crankshaft
stand in place yet!
11. Final assembly and testing.
Attach the piston to its lever arm, and slide the lever
arm into position on the crankshaft. It’ll take some
wiggling. Slide the crankshaft through the middle hole
on the crankshaft stand you glued down. Next, slide
the lever arm for the displacer rod onto the crankshaft,
and attach it to the displacer rod (you may need to
bend the bottom hook). Slide the second crankshaft
stand onto the shaft and line it up. We still don’t want
to glue it in place until we’re done tuning the engine.
Turn the crankshaft. Does anything hang up?
If the piston isn’t pumping properly, is it lined up
where you marked it? If not, remove it and twist the
lever arm until it lines up.
When turning the rod, can you complete a full
rotation? If not, check the displacer disk. Does it
move all the way up and down? If it’s trying to go
too high, move the crankshaft down 1 hole on the
stand. If too low, raise it 1 hole. If it doesn’t make a
complete turn because it’s trying to go too high and
too low, bend shallower cams on the crankshaft.
Bend deeper cams if there’s too much of a gap.
If it turns over nicely, drill a hole the same size
as your rod in the center of your peanut butter lid.
This is your flywheel. Push it onto the end of the
crankshaft closest to the piston cylinder. It should
be a snug fit. Don’t glue it yet.