relationship to each other and the engine, when it is eventually
mounted in place to the firewall.
Prepare the scrap piece of plywood with accurate horizontal and
vertical centerlines, using a pencil and a triangle. Next, measure
the width of your engine case and draw those locations onto the
scrap piece of wood, using the centerline for the measurements.
Note that the two motor mount arms have oblong mounting holes.
This allows you to move either one or both of the arms left or right
as needed. When drilling the mounting holes, use the center of the
oblong holes to allow a little movement in either direction. Drill the
four motor mount holes through the plywood, using a 3/16" dia. bit.
Install the motor mount arms to the piece of plywood, using the
blind nuts, bolts and washers provided. Just hand-tighten the bolts
enough to hold the arms in place.
Slide the motor mount arms left or right to align them accurately to
each side of the vertical centerline.
Once in position, use a
screwdriver to temporarily tighten the bolts just enough to lock the
arms in place.
Place the engine onto the motor mount arms.
Using a ruler, adjust the engine on the mounts to locate the face
of its prop hub at 5-15/16" from the face of the scrap piece of
plywood. Hold the engine in this position and use a drill bit in each
of the engine's mounting lug holes, marking their centered
positions onto the motor mount arms. Remove the engine and
remove the motor mount arms from the piece of plywood.
❑
2) The bolt holes are now drilled through the two motor mount
arms. These four holes should be clearance holes for the bolts you
intend to use. For example, using the Saito 1.50 engine shown
here, we used 8-32 x 1-1/2" socket head bolts. For 8-32 bolts, we
used a #19 (.166) bit to drill the proper clearance holes. If you are
careful, it may be possible to drill these holes by hand. However, we
suggest using a drill press to ensure that these holes are correctly
placed and drilled truly perpendicular to the motor mount arms.
❑
3) The scrap piece of plywood used to mount the engine has
now become a pattern that is used to accurately locate the four
required mounting holes onto the firewall. Hold the pattern against
the firewall and line-up its horizontal and vertical centerlines with
those on the firewall. Hold the pattern in place and use a 3/16" dia.
bit, twisting it a few times, marking the four hole locations onto the
firewall. Remove the pattern and use the same bit and a power
drill to make the four holes through the firewall, at the marks just
made.
❑
4) The four M4 Blind Mounting Nuts are now installed into the
backside of the firewall. To do this, you will have to reach into the
nose compartment, through the top of the fuselage, using your
fingers to feel for the hole. This can be made a lot easier by
inserting a length of 1/8" dowel (7" or 8") through the hole from the
firewall side. When you can see the end of the dowel in the
fuselage, slip one of the blind nuts onto to it and then, pull the
dowel back out of the hole while holding the nut on the dowel from
the inside. This will locate the blind nut to the back side of the hole
every time.
Hold the nut against the firewall with your finger and use one of the
M4 bolts to engage its threads from the front of the firewall. Thread
the bolt all the way in place. Use a screwdriver to tighten the bolt,
"pulling" the barrel of the blind nut fully into the back side of the
firewall, (we ran our bolts through the holes in the plywood pattern
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