Great Planes Extra 300S 1.60 ARF - GPMA1365 - Manual (Page 16)

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2. Make a mark in the center of each block. Using a felt
tip marker draw a 3" [76mm] line back onto the fuselage. Do
this on each of the four mounting blocks.
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3. Locate one 1/8" [3mm] balsa disk, one 1/8" [3mm]
balsa ring and two 1/8" [3mm] balsa rings. Glue the 1/8"
[3mm] balsa ring onto the 1/8" [3mm] balsa disk, carefully
aligning the outer edges. Glue the two 1/8" [3mm] rings
together forming a 1/4" [6mm] ring. Glue the 1/4" [6mm]
balsa ring onto the 1/8" [3mm] balsa ring, carefully aligning
the inside edges.
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4.These disks will now be an alignment tool for centering the
cowl. The hole in the center of the plywood plate is designed to
fit the crankshaft of an O.S.
® 1.20. If you are using a larger
engine than the 1.20, the crankshaft is most likely larger. Use
a propeller reamer to make the hole in the center of the
plywood plate fit your particular engine crankshaft.
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5. Install the cowl over the engine. Slide the alignment
tool over the crankshaft and firmly against the engine thrust
washer. Tighten the prop nut and washer against the
plywood plate. With the alignment tool tight to the engine
thrust washer, slide the opening in the cowl over the
alignment tool. When the front of the cowl is tight against the
alignment tool the cowl is properly centered and is
positioned for the proper clearance between the spinner
back plate and the cowl.
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6. Keeping the cowl tight against the alignment tool,
position the cowl so the paint lines on the cowl and fuselage
are in alignment with each other. When properly positioned,
tape the cowl in place to the fuselage.
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7. Measure 3" [76mm] back to the cowl from the end of
the reference lines you made. Drill a 3/32" [2.4mm] hole
through the cowl and into the cowl mounting block. Install a
#4 x 1/2" [13mm] sheet metal screw and a #4 flat washer
into each of the holes drilled. Remove the alignment tool
after the cowl has been secured with the four screws.
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8. Remove the cowl. Put a couple of drops of thin CA into
the holes in the mounting blocks to harden the threads.
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9. Cut a piece of card stock 2" x 10" [51 x 254mm]. Tape
it to the side of the fuselage in line with the glow plug. Mark
the location of the glow plug on the card stock. Re-install the
cowling so the card stock is outside of the cowl. Transfer the
glow plug location to the cowl and cut the hole for the glow
plug using a high speed rotary tool. Use this same
technique for locating the needle valve.
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