18
MOUNTING THE COWLING AND SPINNER
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1) Drill two 1/8” dia. holes in each side of the cowling at the
locations shown here. The dimensions are based from the center
of the last exhaust pipe that is molded into the side of the cowling.
Using a felt-tip pen, draw a horizontal line straight back from the
center of the last exhaust pipe. Draw another line parrallel to the
back edge of the cowling, exactly 7/16” away from the edge.
Where the parrallel line and the exhaust center line intersect, that
is the location for the top screw hole. The bottom screw hole is
located exactly 3” below the top hole, measured along the parrallel
line.
Once you have the holes marked on both sides of the cowling, drill
them with a 1/8” dia. bit, using a backing block of scrap wood to
support the cowl as it is being drilled. Clean up the drilled holes by
sanding the inside of the cowling lightly with fine sandpaper.
❑
2) Try fitting the cowling over your engine and back onto the
fuselage. If you have a typical engine installation (a single-cylinder
engine mounted inverted), you will probably find that you need to
make an opening in the bottom of the cowling for the engine
cylinder to stick through. Looking through the spinner opening,
watch carefully to see where the head of the engine first hits the
inside of the cowling and mark that spot with a pencil or felt tip
marker. Remove the cowl, and use a Dremel
®
Tool to make a small
opening in the cowl at the point of contact.
Refit the cowl,
checking the hole location and size, adjust as needed and again
use the Dremel
®
Tool to make the opening bigger. Keep refitting,
remarking, and readjusting the hole until the cowling can be
slipped over the engine into correct position on the fuselage. As a
general rule, you should end up with at least 3/16" clearance
between the cowling and any engine part.
Note: On page 26, we’ve provided a full-size pattern of the opening
we put in our cowl for the Saito 1.00 4-stroke engine shown in the
pictures. If you are using the same engine, or one very similar, the
pattern will provide a good starting point for your cutout.
SAFETY ISSUE: Whenever working with fiberglass, always
use a facemask and safety glasses!
❑
3) Once you can get the cowling in proper position on the
fuselage without any part of the engine contacting the cowl, mount
your spinner backplate and propeller on the engine prop shaft.
Tighten the prop assembly sufficiently to bring the spinner
backplate firmly in contact against the engine's prop mounting
flange. Now, check to see that you have at least a 1/16" gap
between the back of the spinner backplate and the front of the
cowling (1/16" to 1/8" is OK).
Adjust the final location of the
cowling, making sure that the spinner backplate is centered at the
front and that the back edges of the cowl are tight against the
fuselage.
Use masking tape to hold the cowling securely in
position on the fuselage.
With the cowling taped in place, mark the cowl mounting screw
positions onto the fuselage through the pre-drilled holes in the
cowl. Remove the cowl and use a 3/64" (or #56) dia. bit to drill pilot
holes in the fuselage at the marks just made. After drilling the
holes, screw in the four T2.6 x 8 mm PWA Screws provided for
mounting the cowl. Run the screws in and back out a couple times
to create good threads in the wood. Then, take the screws back
out and place a small drop of Thin CA glue in each hole. Let dry
and then, run the mounting screws in and out again. This hardens
the threads in the wood, making them tough and durable enough
to hold up to dozens of cowl removals and installations.
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4) Figure out what size and shape opening you will need in the
cowling to accommodate your engine's muffler, and cut it out now.
❑
5) Figure out how you are going to light your glow plug and
whether that will require an opening in your cowling.
Note: One option, that requires no cowling changes, would be to
use a "remote" glow plug wiring harness (not supplied). Another
option, as shown here with our Saito 1.00 installation, was to use
an extended glow plug battery igniter (not supplied), and make
another small slotted hole in the bottom of the cowling, just behind
the engine head cutout. Position the hole to allow the glow igniter
to line up perfectly with the glow plug.
IMPORTANT SAFETY ISSUE!
DO NOT DRILL AND TAP THE GLASS-FILLED ENGINE MOUNTS
FOR BOLTS, OR USE SELF-TAPPING SCREWS OR WOOD
SCREWS.
THOSE METHODS WILL WEAKEN THE ENGINE
MOUNTS AND CAN LEAD TO ENGINE MOUNT FAILURE!
1) Use only Socket-Head Bolts with Aircraft Lock Nuts and Flat
Metal Washers to fasten your engine to the glass-filled engine
mounts, as shown in these instructions.
2) The holes you drill through the mounts must be big enough for the
engine mounting bolts to pass freely through. The bolts should not go
in tight. In the case of 8-32 mounting bolts, a 11/64" dia. drill bit will
provide proper clearance holes. For 10-32 bolts use a 13/64” drill bit.