hole 1/4" away from the half circle cut out, on each side. Center
these holes exactly in the center of the lite-ply and drill them both
to a depth of 3/8”. Thread a 1/4” socket head cap bolt all the way
into each insert. Coat the outer threads of the insert with a little
5-minute epoxy and use an Allen head driver to install both inserts
fully into and flush with the top of the mount. Remove the two Allen
head bolts and allow the glue to cure.
d) A simple aluminum muffler "clamp" is now made from a
piece of scrap .03 (1/32”) aluminum sheet. Use tin snips to make
a strip of this material 1/4” wide x 4" long. Round the corners of
one end with sandpaper.
From the tip of the rounded end,
measure and mark a point at 3/8”. Now measure and mark a point
in the center of the strip, 3/16” from the end. Drill a hole through
this point using a 7/64” dia. bit. At the 3/8” mark, bend the strip 90
O
to the drilled end "tab". Now bend and form the strip around the
muffler body, creating a half-circle shape. Place the muffler into the
mount and then secure the drilled "tab" end of the strip to the
mount with a 4-40 x 1/4” socket head bolt.
Mark a bending
location on the opposite side of the aluminum strip, about 3/32" -
1/8” above the mount, where it must be bent to create a second
mounting "tab". Remove
the aluminum clamp and
bend it at 90
O
at the mark
just made.
Trim off the
excess strip material to
leave a 3/8” "tab" length.
Drill a hole in center of
this tab for the 4-40
mounting bolt, using
a 7/64” dia. bit.
Clean
up and deburr the
aluminum clamp with
sandpaper.
e) Last, we wanted to
cushion the muffler when it
is clamped in place into
the muffler mount. To do
this we slit a piece of heat
resistant neoprene tubing
lengthwise and placed it
over the half-circle cut out,
holding it in place with
silicon glue. This custom
muffler mount is now
complete and ready to
install into the fuselage.
This will take place shortly
so the mount handy.
❑
9) The MAC's Products #9114 aluminum exhaust diverter is
now fitted to the exhaust tube on the muffler. This diverter uses a
c) The flex tube header can now be bent into the desired
configuration. This tube bends surprisingly well and will hold its
shape provided you over-bend it a little. Continue bending the tube
and placing the engine back on the mount arms to check your
progress. The goal is to bend the tube to clear it from any contact
with the cowl and to wind up with the muffler end of the tube
aligned with the muffler's header mounting location, with the
muffler aimed directly back from behind the engine head.
Be
patient and periodically check your progress by placing the engine
on the mount arms. When the flex tube is bent to about the correct
configuration, consideration to mounting the muffler firmly to the
fuselage must be addressed.
❑
8) The muffler mount is now made. This is an optional step
and is included to illustrate how we accomplished our own
mounting system. This muffler mount is basically a scrap piece of
1/8” lite-ply, cut to fit on edge into the recessed opening at the
bottom front of the fuselage, behind the cowl. Carefully note that
the top of this opening is the fuel tank floor, and therefore no holes
should be drilled through it.
a) Using a pencil and triangle, measure, mark, and cut
a piece of 1/8” lite-ply to create a rectangle measuring
15/16” x 2-3/8”. Use a sanding block to dress the two 15/16” sides
until the rectangle fits upright into the recessed opening, uniformly
contacting the sides and bottom. Measure and mark the center of
the mount (1-3/16”) and use a triangle to mark this centerline onto
the mount. From the bottom of the mount, measure up 3/8” at the
centerline and mark this point. At the centerline, use a circle guide
to accurately draw a 1-1/8” dia. half circle, with the bottom of the
circle at the 3/8” mark just made (this circle size is just a bit larger
in diameter than the diameter of our muffler at the location it will be
mounted). Use a jigsaw to now cut-out the half-circle from the
former and sand off any rough edges
b) Cut two 2-3/8” lengths of 1/8” x 1/4” spruce. Use 30-minute
epoxy to glue one piece of spruce to each side of the muffler
mount, at the top where the half circle cut out is widest. Use a vise
or weights to clamp this assembly firmly together and allow the
glue to cure.
c) Sand the ends of the spruce pieces flush with sides of the
mount. With a jigsaw, remove the excess 1/8” x 1/4” spruce from
within the half-circle area of the mount. We prefer to use 4-40
socket head hardware for mounting and securing the muffler. With
this in mind, we used a pair of Du-Bro #391 4-40 Threaded Inserts
and a pair of 4-40 x 1/4” Socket Head Cap Bolts for our muffler
clamp. These threaded inserts are installed into the top of the
muffler mount, between the two spruce pieces. To do this first drill
two 3/16” dia. holes into the top of the muffler mount, locating each
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