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the proper number of washers, correcting spring tension,
and re-adjusting the setting could solve the
problem.
(iii) An internal problem within the
engine (most likely the oil pump): An engine tear
down would be required.
(3) With good oil pressure/temperature
readings and the engine running smoothly, ensure
that the engine oil pressure and temperature gauges
in the cockpit match the calibrated oil pressure and
temperature gauges, which were attached to the aircraft
for the first run. Do not overlook this test. It
is critical to determine the accuracy of the cockpit
engine gauges not only for the ground engine runin
period, but for in-flight engine cooling tests.
(4) Work through the engine manufacturer’s
run-in schedule. The majority of the engine
manufacturers recommend a series of engine runs
from low rpm to maximum rpm. Each run usually
incorporates a 200 rpm increase and lasts no longer
than 10 minutes. The secret to a successful engine
run is not to let the engine temperatures exceed
manufacture’s limits during engine runs.
NOTE: Engines with chrome cylinders or
chrome rings require different high power
run-in programs. Follow the manufacturer’s
run-in instructions to ensure the engine will
perform satisfactorily over its lifetime.
h. Engine Cool Down: After a ground-run, the
cooling off period takes approximately an hour. This
is because a newly overhauled engine needs time
for the internal parts (e.g., rings, cylinders, valves,
bearings, and gear faces) to expand and contract several
times to obtain a smooth surface that retains
its ‘‘memory.’’ This is a lengthy process even when
done right, but it is important not to skip any of
the recommended runs to save time. To do so is
to risk increasing oil consumption and reducing overall
engine performance, reliability, and engine life
span -- which could be costly in the long-term.
i. Record the engine run-in data: During the
engine run, monitor the cylinder head temperatures,
oil temperature, and oil pressure. Record the readings
and adjustments for future reference. If the cylinder
head temperatures are rising close to the red line,
reduce power and stop the test. Some causes of high
cylinder head temperatures include using spark plugs
with the improper heat range; cylinder head temperature
gauges installed on the wrong cylinder; missing
or badly designed cylinder head cooling baffles; partially
plugged fuel nozzles (applicable to fuel
injected engines); fuel lines of improper internal
diameter (creates lean mixtures); engine improperly
timed either mechanically and/or electrically; and the
carburetor fuel mixture set excessively lean.
j. After shut-down:
(1) After each engine run, check for fuel
and oil leaks, loose connections, and hot spots on
cylinders (burnt paint). The FAA recommends draining
the oil and removing the oil screen/filter within
the first 2 hours of running the engine. Check the
screen/filter for ferrous metal with a magnet. Wash
and inspect the screen/filter for non-ferrous metal
like brass, bronze, or aluminum.
(2) A very small quantity of metal in the
screen is not uncommon in a new or newly overhauled
engine. It is part of the painful process of
‘‘running-in.’’ If subsequent oil screen checks
(2 hours apart) show the engine is ‘‘making metal,’’
this indicates a problem inside the engine and a tear
down inspection is required.
(3) It also is recommended all fuel sumps,
filters, and gasolators be checked for debris after
each engine run. Special attention should be given
to the fuel system by the builder who constructed
fuel tanks out of composite or fiberglass materials.
Composite and fiberglass strands can be very fine,
making visual detection difficult. Frequent cleaning
of the fuel filters and screens early in the flight testing
phase will avoid a gradual build up of loose
composite fibers, which would reduce or stop the
flow of fuel to the engine.
22
AC 90-89A 5/24/95
SECTION 11. ADDITIONAL ENGINE TESTS
‘‘Always go with the best fix not the cheapest fix.’’ Bill Deeth, Master Mechanic (1994)
1. OBJECTIVE. To determine if the engine supply
of fuel is adequate at all angles of attack.
a. Mixture and Idle Speed Check: After
completing the initial engine ‘‘run-in’’ tests, check
the idle speed and mixture settings. To determine
if the mixture setting is correct, perform the following:
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