20
RUNNING-IN ("Breaking-in")
For long life and peak performance, every engine needs
special treatment when new, know as “running-in” or
“breaking-in”. This is a procedure during which the
engine is operated under strictly controlled conditions at
the beginning of its life, in order to avoid the risk of
immediate damage to certain components through
becoming overheated or stressed and to help working
surfaces to become smoothed and aligned for maximum
mechanical efficiency thereafter. With some engines, this
can require a tediously protracted period of bench
running, but, as O.S. engines are manufactured to fine
tolerances and from the finest quality materials, a
relatively brief running-in period is sufficient and can be
completed with the engine installed in the aircraft.
Prolonged running with too rich a mixture and/or low
speed will not complete the proper running-in. On the
other hand prolonged low speed running may cause an
excessive varnish build up which may result in seizure of
the piston and cylinder liner.
The recommended procedure is as follows:
Use the same fuel and prop as you intend for flying your
model.
1.
2.Open the needle-valve 2.5-3 turns from the fully closed
position and start the engine.
3.Open the throttle slowly to the mid speed position, and
disconnect the current to the glowplug.
4. Now open the throttle slowly to the fully opened position
and run the engine for no more than 5 seconds with the
needle-valve tuned to produced near maximum r.p.m.,
then, immediately, slow the engine down again by opening
the needle-valve approximately one turn. The rich mixture,
so induced, will cool the engine, at the same time providing
increased lubrication.
5.
WARNING:
When ground running the engine, avoid dusty or sandy
locations. If dust or grit is drawn into the engine, this can
have a ruinous effect, drastically shortening engine life in
a matter of minutes.
Repeat this process, alternately running the engine fast
and slow by means of the needle-valve, while keeping the
throttle fully open, then begin to extend the short periods of
high-speed operation until two tanks of fuel have been
consumed.
21
With each successive flight, close the needle-valve very
slightly until, at the end of about 10 flights, the needle is set
for full power. Do not "over-lean" the mixture in an attempt
to extract more power.
8.
If overheating should be suspected at any time during
flight (i.e.if the engine begins to "labor") reduce power by
partially closing the throttle and land the aircraft to
enable the needle-valve to be readjusted to a richer
setting.
Following the initial running-in session, check for any
looseness in the installation due to vibration, then allow the
engine a period of moderately rich operation in flight.
6.
For the first flight, have the needle-valve set on the rich
side and adjust the throttle trim on the transmitter so that
the engine does not stop when the throttle is closed to the
idle setting.
7.
Note:
Remember that, when the engine is not yet fully run-in,
the carburettor cannot be expected to give its best
response in flight. Abrupt operation of the throttle, for
example, may cause the engine to stall. Therefore, at this
time ,the aircraft should, as far as is possible, be flown at
an altitude sufficient to enable an emergency landing to
be safely made if the engine stops.
Once the engine has demonstrated that it can be safely
operated at full power, the carburettor can be adjusted for
optimum throttle response, following the instructions given
in the next section.
9.
