Sonex Fuel Tank Installation Tips - Manual

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sonex aircraft
, LLC
Builder's Guide Fuel Tank Installation and Warranty
Preparation
The filler neck may need to
be trimmed in height, so the
filler cap is below the top
of the filler box (see photo
below). This can be accom-
plished in advance of fuel
tank installation with a hand
saw, or with a cut-off disk in
a motor tool after the tank is
installed. If you trim the neck
with the tank installed it is
more difficult to remove the
debris from the tank.
Filler Neck
The inside diameter of the
fuel tank's neck may need to
be enlarged slightly to allow
the adjustable-diameter rub-
ber fuel cap to be installed.
This can be done with a half-
round file, a razor knife, or a
drum sander in a motor tool.
The filler neck may need to be trimmed in height so the fuel
cap does not protrude above the top of the filler box as shown
in this photo.
Clean the Threaded Inserts
The threaded inserts are molded in to the plastic and MUST be
cleaned of molded plastic before fittings are installed.
IMPORTANT: Failure to clean the inserts can result in the
threaded inserts loosening in the tank when fittings are in-
stalled. This is not covered by the fuel tank warranty.
Caution: NPT threads are tapered. Do not run the tap all the
way in to the insert or you will destroy the taper and affect the
fuel-tight seal when the fitting is installed. Run the tap in until
slight resistance is encountered and the threads appear clean.
Large Insert
1. Carefully run a 1/2" diameter drill through the large insert
in the fuel sump.
2. Run a 3/8 NPT tap into the insert to clean the threads.
Small Inserts
1. Carefully run a 19/64" diameter drill through the remain-
ing (small) holes in the tank
2. Run a 1/8 NPT tap into the inserts to clean the threads.
Oops Fittings
Sonex Aircraft offers Oops Fittings to replace the threaded
inserts if necesary/desired. Oops Fittings can replace threaded
inserts that leak from improper installation but some builders
choose to install Oops fittings during initial installation. See
page 3 for more information.
Clean the Tank
DANGER! Fuel vapors are explosive! If you clean your
tank with fuel or mineral spirits do so in a well-ventilated
area, away from open flame or other ignition sources, and
remember that fuel vapors will linger in the tank after the
liquid has been removed.
The tank must be thoroughly cleaned of debris.
Install the Fittings
Apply teflon paste to the threads of each fitting before install-
ing them. Do not use tefon tape. The fuel fittings can be
installed before the tank is installed in the airframe.
Important: Do not over-tighten the fittings as this can break
an insert loose in the tank. This is not covered by the fuel tank
warranty. It takes only a snug, not tight, fit to achieve a leak-
proof installation.
After the fittings are installed you may wish to plug each fit-
ting and perform a leak test with a small amount of gasoline or
mineral spirits.
DANGER! Fuel vapors are explosive! If you leak-test the
tank with fuel or mineral spirits do so in a well-ventilated
area, away from open flame or other ignition sources, and
remember that fuel vapors will linger in the tank after the
liquid has been removed.
Rev C. 03/05/10
IMPORTANT! Read this entire instruction sheet before install-
ing the fuel tank.