O.S. engine MAX-75AX-BE Instruction Manual page 15

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
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.
3. Re-start and adjust the needle-valve so that
the engine just breaks into a "two-cycle" from
"four-cycle" operation, then make three or four
flights, avoiding successive "nose-up" flights.
4. 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 richer. After a total of ten flights, the
engine should run continuously, at its
optimum needle-valve setting, without loss
of power as it warms up.
5.
After the completion of the running-in adjust
the carburetor at optimum setting referring
to MIXTURE CONTROL
ADJUSTMENT section and SUBSEQUENT
READJUSTMENT section.
RUNNING-IN ("Breaking-in")
1.
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
temperature.
battery is 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 needle-valve
adjusted for rich, slow "four-cycle"operation.
2. 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 needle-valve to bring the engine back to
"four-cycle"operation and run it for another
10 seconds. Repeat this procedure until the
fuel tank is empty.
28
Optimum needle setting(1)
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)
Optimum needle setting(2)
As the needle-valve is closed slowly and grad-
ually, the engine r.p.m. will increase and a
continuous high-pitched exhaust note, only,
will be heard. Close the needle-valve 10-15
degrees and wait for the change of r.p.m.
After the engine r.p.m. increases turn the nee-
dle-valve another 10 - 15 degrees and wait for
the next change of r.p.m. As the speed of the
VALVE
engine does not instantly change with needle-
valve readjustment, small movements, with
pauses between, are necessary to arrive at the
optimum setting.
29