SCIENCE
E
F
GH
Fig. E: Crank bearing assemblies mounted onto the base.
Fig. F: Exhaust port cut into the bottom of the cylinder.
Fig. G. Spark points (drywall screws) form a spark
gap inside the cylinder.
using a hole saw. Using clamps and a straightedge
as a fence, cut along each line to create 2 identical
arch-shaped pieces.
Mount the 2 saddles to the forward crank support, on the opposite side from the bearing, using
1½" corner braces. Position one flush with the top
and the other 7" down. For traction, line the arches
with 1" adhesive tread (Figure C).
For the cylinder hold-downs, use 2 lengths of ¾"
brass pipe strap. Drill 5" pilot holes on either side
of each saddle for mounting screws, and do a “dry
run” securing the 2" PVC in place (Figure D).
4. Mount the crank bearing assemblies.
Mount the 2 crank bearing assemblies to the top of
the base, 6" in from each end, with the bearing sides
facing each other. Use a square to make sure the
supports are vertical and parallel, and secure them
with pairs of 3" corner braces on each side. Offset the
braces by ½" so their screws don’t clash (Figure E).
5. Make the cylinder.
Use the Dremel to cut an exhaust port in the 2" PVC
pipe about 11" high by 1½" wide, and 7" from the
end (Figure F). Chamfer the inside bottom of the
cylinder to give clearance for the connecting rod.
162 Make: Volume 13
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Fig. H: PVC end cap piston connects to the dowel
connecting rod with wrist pin and nylon spacers.
Fig. I: Galvanized pipe crankshaft and pipe flange
crank with a bolt running through the connecting rod.
6. Insert the spark points.
Mark the circumference of the cylinder at 11½" and
20½" from the bottom. Through each line, drill 2
pilot holes spaced 120° straight into the center.
Screw in 4 drywall screws until the tips of each pair
lie ¼" to 2" apart inside the pipe (Figure G).
Test the points by linking one from each pair
together with an alligator clip jumper, then run
leads from the 2 free points to the grill igniter.
Push the igniter button, and you should see 2
sparks. If not, disconnect, tighten the screws to
bring the points closer together, and try again.
7. Mount the cylinder head.
Fit the PVC end cap, or adapter with screw plug,
onto the cylinder (the end cap makes a “hemi” style
head, while the adapter and plug let you examine
the sparking more easily). Secure with 3– 4 screws.
Marking PVC Pipe Straight Across
One way to mark a pipe evenly for cutting is
to lay it in the corner of a box or drawer, hold
a pencil down at the measured marking point,
and rotate the pipe underneath until the pencil
mark goes all the way around.
Find more tools-n-tips at makezine.com/tnt.
