RUNNING-IN (Breaking-in)
All internal-combustion engines benefit from extra
care when they are run for the first few timesknown
as running-in or breaking-in.
This allows the working parts to mate together under
load at operating temperature. Therefore, it is vitally
important to complete the break-in before allowing the
engine to run continuously at high speed and before
finalizing carburetor adjustments.
However, because O.S. engines are produced with
the aid of the finest modern precision machinery and
from the best and most suitable materials, only a
short and simple running-in procedure is called for
and can be carried out with the engine installed in the
model. The process is as follows.
Install the engine with the propeller intended for
your model. Open the needle-valve to the advised
starting setting and start the engine. If the engine
stops when the glow plug battery disconnected,
open the needle-valve to the point where the engine
does not stop.Run the engine for one minute
with the throttle fully open, but with the needlevalve
adjusted for rich, slow "four-cycle"operation.

Now close the needle-valve until the engine
speeds up to "two-cycle"operation and allow it to
run for about 10 seconds, then reopen the needlevalve
to bring the engine back to "fourcycle"
operation and run it for another 10 seconds.
Repeat this procedure until the fuel tank is empty.
Re-start and adjust the needle-valve so that the
engine just breaks into "two-cycle" from "fourcycle"
operation, then make three or four flights,
avoiding successive "nose-up" flights.
During subsequent flights, the needle-valve can be
gradually closed to give more power.
However, if the engine shows signs of running too
lean, the next flight should be set rich. After a total
of ten to fifteen flights, the engine should run
continuously, on its optimum needle-valve setting,
without loss of power as it warms up.
After the completion of the running-in adjust the
carburetor at optimum setting referring to
MIXTURE CONTROL VALVE ADJUSTMENT
section and SUBSEQUENT READJUSTMENT
section.

Slowly advance the throttle to its fully open position,
then gradually close the needle-valve until the
exhaust note begins to change. (4-cycle to 2-cycle)
At this point, disconnect the battery from the
glowplug, taking care that the battery leads or
glowplug clip do not come into contact with the
rotating propeller. If the engine stops when the
battery is disconnected, close the needle-valve about
30° and restart.
As the needle-valve is closed slowly and gradually,
the engine r.p.m. will increase and a continuous highpitched
exhaust note, only, will be heard. Close the
needle-valve 10-15° and wait for the change of r.p.m.
After the engine r.p.m. increases turn the needlevalve
another 10-15° and wait for the next change of
r.p.m. As the speed of the engine does not instantly
change with needle-valve readjustment, small movements,
with pauses between, are necessary to arrive
at the optimum setting.