O.S. Engines FS-52S - Manual (Page 16)

8. Now disconnect current to the glowplug and
gradually close the needle-valve so that the rpm
increases. Make adjustments to the needle in small
steps. Abrupt changes at this stage are likely to
cause the engine to stall. Restart the engine by
simply applying the starter with the glowplug re-
energized and the throttle at its starting setting.
RUNNING-IN ("Breaking-in")
For long life expectancy and maximum performance
every engine requires a break-in period under
controlled conditions in order to avoid over-heating
that could damage the internal parts while they are
being smoothed and polished together.
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.
Start and adjust the engine as detailed in the starting
instructions.
Now open the throttle fully and run the engine for no
more than 5 seconds with the needle-valve tuned to
produce near maximum r.p.m., then, immediately,
slow the engine down again by opening the needle-
valve approximately 1/2 turn. The rich mixture, will
cool the engine, at the same time providing ample
lubrication.
Allow the engine to run like this for about 10
seconds, then close the needle-valve again to
speed it up to near maximum speed for another 5
seconds.
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
full tanks of fuel have been consumed.
WARNING:
When ground running the engine, avoid dusty or
sandy locations. If dust or grit is drawn into the
engine, this can have a damaging effect, drastically
shortening engine life in a matter of minutes.
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The recommended procedure is as follows :
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