14
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 0.5 turn.
The rich mixture, so induced, will cool the engine, at the
same time providing increased of 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 rpm 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.
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.
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.
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.
RUNNING-IN (continued)
1.
2.
3.
4.
5.
6.
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.
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.
7.
8.
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.
RUNNING-IN ("Breaking-in")
For long life and peak performance, every engine needs
special treatment when new, known as "running-in" or
"breaking-in". This is a process 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.
The recommended procedure is as follows :
15
Start the engine, open the throttle fully and set the needle-
valve slightly rich (30-45
°
) from the highest r.p.m. setting.
Close the throttle to the idle position. Allow the engine to
idle for about 5 seconds, then reopen the throttle. The
engine should accelerate smoothly back to full speed.
If, instead, the engine responds sluggishly and emits an
excess of white smoke from the exhaust, the idle mixture is
too rich. Turn the mixture control screw approx. 45
°
clockwise to lean the idling mixture.
On the other hand, if the engine hesitates before picking up
speed or even ceases firing completely, the idle mixture is
likely to be too lean. Turn the mixture control valve 90
°
counter-clockwise to substantially enrich the mixture, then
back again 45
°
clockwise.
IDLE MIXTURE ADJUSTMENT
In paragraphs 3 and 4 above, the 45
°
total movements are,
of course, approximate. It will be necessary to fine-tune the
mixture control screw 10-15
°
at a time to reach the best
setting for optimum throttle response.
Continue re-checking the idle mixture setting until the
engine responds smoothly and positively to operation of
the throttle at all times.
In the course of making carburetor adjustments, it is just
possible that the mixture control valve may be inadvertently
screwed in or out too far and thereby moved beyond its
effective adjustment range.
Realignment of Mixture Control Valve
1.
2.
3.
4.
5.
6.
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.
The basic (factory) setting is as shown in the main sketch, i.e.
with the shoulder portion 'A' exactly at a tangent to the throttle
rotor hole. To return the mixture control valve to its original
position, first screw in the mixture control valve, while looking
into the rotor hole. Then graduakky unscrew the mixture
control valve until 'A' is precisely tangential to the rotor hole
(i.e. so that 'A' and 'B' are superimposed) as in the main
sketch.
Its basic setting can be reestablished as follows:
Mixture control valve
Nozzle
Throttle rotor hole
CARE & MAINTENANCE (laying up)
The fuel pump assembly, carburettor/pressure-regulator and
silicone tubing must be cleansed separately in methanol or
glow fuel. On no account must they come into contact with
kerosene. Before completely reassembling the engine, make
sure that no kerosene remains inside that could find its way
into the pump unit, carburettor, etc.Inject, sparingly,
preserving oils, rust inhibitors, etc.
Debris tends to
accumulate in
this area
unless approved for silicone-
rubber products. An appropriate
alternative here may be one of the
high-quality synthetic lubricating
oils. Finally, seal the engine in a
heavy polyethylene bag until
required for reinstalling in the
airframe.
