Great Planes Piper J-3 Cub 40 Kit - GPMA0160 - Manual (Page 28)

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20. Insert the die-cut 1/8" ply Top Deck Former #4
(CUB4F11) into its slot at the tail end of the balsa aft fuse
top. Slide the die-cut 1/8" ply Stab Base into its position
behind TDF #4 so that it keys into the former. Pull the
fuselage sides in to meet the former and stab base, and
securely glue the stab base only in place. (Note: Do not
glue TDF #4.) Remove the turtle deck former for now.
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21. Go back and securely glue all formers by applying
more thin CA, if needed, and then thick CA to each joint.
Note: The 1/8" Firewall Doubler (spacer) is used, as needed,
to position the engine at the desired distance from the
firewall. Depending on your engine size, you may have to use
two or even three spacers to achieve the correct spacing.You
may cut the extra die-cut firewall (CUB4F04) to 2-3/8" x 2-
3/8" and use it as an extra spacer. The plans show the thrust
washer at 5", but 5-1/8" is best. Do not glue these spacers in
at this time. When you later fit the cowl, you may decide to
adjust the fore-aft position of the engine slightly.
NOTE: If you are using a 4-Cycle Engine, skip to step #3.
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1. Draw two lines on the 1/8" x 2-3/8" x 2-3/8" Firewall
Doubler (CUB4F18) that extend from one corner across to
the diagonal corner as shown in the photo. This spacer is
not required for most 4-cycle engines.
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2. Place the left side of the engine mount on the mount
spacer and center it on the diagonal lines you just drew. Mark
the mounting holes on the diagonal lines and then drill a 3/16"
hole at each mark. NOTE: You will not glue this doubler to the
firewall. It is used as a spacer only. Later, if you decide to
change to a 4-cycle engine, you can easily remove the spacer.
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3. Determine whether you want your engine side mounted
or inverted. We recommend side mounting, but an inverted
engine may allow you to use two dummy engines on the cowl.
Screw the mount to the firewall using the 6-32 x 1" machine
screws (SCRW008) provided. If you are using a 2-cycle
engine, place the 1/8" spacer you just drilled between the
mount and the firewall.
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4. Set the engine on the engine mount and measure from
the firewall to the front of the thrust washer. Adjust the engine
on the mount until the front of the thrust washer is 5-1/8"
[130mm] away from the face of the firewall. Mark the
mounting hole locations on the mount. Remove the engine
from the mount and accurately drill 7/64" (or #36) holes.
NOTE: If you have access to a drill press, use it for drilling
these holes to insure that they are drilled vertically.
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5. Now you may use one of the following methods to
attach your engine to the mount:
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Method 1: Screw the #6 x 3/4" sheet metal screws
(SCRW018), provided in the kit, through the engine
mounting flange and into the mount. When first installing
these screws, put a drop of oil into each screw hole.
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Method 2: Cut threads in the holes you just drilled
using a 6-32 tap and tap wrench. If you use this method
you’ll have to supply your own bolts (6-32 x 1" socket head
cap screws) for attaching the engine to the mount.
Install Engine Mount and Fuel Tank
28