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SECTION 1. ENGINE INSPECTION
1. OBJECTIVE. To provide the amateurbuilder/
ultralight pilot with a suggested engine and
fuel system inspection program in addition to the
manufacturer’s check list items.
a. Engine.
(1) Check the engine mount, vibration isolation
mounts, and attach points before each flight.
NOTE: If slippage marks are painted across
the bolt heads, engine mount, and fuselage
at the time the mount bolts are torqued, a
break in the paint will give advance warning
the mount is coming loose. (Again, red nail
polish works adequately.)
(2) Check all hose clamps for tightness.
(3) Check for fuel and oil leaks.
(4) Check air filter for condition and
attachment
(5) Ensure that all spark plugs are the correct
ones, properly torqued. Check that the ignition
wires, caps, and plug cap restraints on inverted
engines are secured and safetied. Ensure that the kill
switch, if applicable, is within easy reach and works
as advertised.
(6) Check that the carburetor and the throttle
cable is secured and both operate freely from idle
stop to full power stop.
(7) Check carburetor boots for cracks that
will suck air and may create a lean mixture, high
CHT and EGT, and possible engine failure.
(8) Check the fuel on/off valve, fuel filter,
and crossover valve for proper operation and
position.
(9) Drain the fuel system of water and
sediment.
(10) Ensure that the fuel tank is secured,
full, and if applicable, contains the proper mix (ratio)
of fuel and oil.
72
AC 90-89A 5/24/95
b. Exhaust System.
(1) On most 2 cycle engines, the exhaust
system is tuned to the engine in order to have the
proper amount of back pressure. Sometimes, due to
installation demands, the exhaust system must be
modified. If modifications are necessary, contact the
engine manufacturer before incorporating any
exhaust systems changes.
(2) The exhaust system should be mounted
on vibration-damping elements and be safety wired.
The exhaust system ball-joints should not be
mounted under a tension load and they should be
lubricated with an anti-seize, heat resistant grease
to allow the ball joints to move freely. Some exhaust
systems use springs to keep pressure (compression)
on the ball-joints. If the engine is so equipped, run
a piece of safety wire through the spring and secure
it to the exhaust system. This would prevent a broken
spring from coming loose and hitting the propeller
in a pusher configuration or hitting the top of the
wing or tail in a tractor design.
(3) Another approach to prevent propeller
damage from broken springs is to lay a bead of high
temperature silicon length-wise across the spring. If
a spring does break during flight, the silicon bead
will hold some or all of the broken pieces of spring
material in place until the aircraft lands.
c. Fan Cooling.
(1) It is particularly important that installations
of fan cooled engines with enclosed cowlings
are designed so that the hot cooling air exits the
cowl and cannot recirculate back into the cooling
fan intake. If there are any doubts, tests should be
carried out by measuring the temperature of the air
entering the cooling fan.
(2) In most cases, it is unlikely there will
be a problem with cooling belt tension on a new
engine. On older engines, however, the belt may
have bedded down in the V of the pulley causing
a significant reduction in belt tension. If corrosion
is present on a pulley, the belt wear rate will be
rapid. During the visual inspection of the fan cooling
belt and pulley, look for evidence of wear and corrosion
on the pulleys.
d. Reduction Drive.
(1) A large percentage of engines used on
light-weight aircraft are 2 cycle air cooled engines
fitted with a rpm reduction drive. The reduction drive
is usually a bolt-on unit which drops the high 2 cycle
engine rpm down to a propeller RPM that is more
efficient.
(2) To check tension on most V belts on
the reduction drive, grab the belt and twist. The belt
should allow no more than approximately a half a
turn.
(3) Ensure that the reduction gear box is
filled with oil to the proper level in accordance with
the manufacturer’s instructions and drain plug/filter
is safetied.
(4) Grasp the propeller (switch off and
spark plugs disconnected) approximately half way
down each blade. Try first to move the prop in an
up and down motion. Pull away from the aircraft
and then push in the opposite direction. No appreciable
bearing slop should be detected in the reduction
　
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