20
PROPELLER
There is a risk, particularly with powerful four-
stroke engines, of the propeller flying off if the
prop nut loosens due to detonation
("knocking") in the combustion chamber when
the engine is operated too lean, or under an
excessively heavy load.
Obviously, this can be very hazardous. To
eliminate such dangers, the O.S. Safety
Locknut Assembly was devised.
Install this as follows:
Install the prop to the engine shaft, followed
by the retaining washer and prop nut and
tighten firmly with a 12mm wrench. (not
supplied).
2.
1.
Add the special tapered and slotted locknut
and secure with a 10mm wrench (not
supplied) while holding the prop nut with the
12mm wrench.
Propeller washer
Propeller nut
Locknut
Make a habit of always checking the
tightness of the propeller before starting
the engine. Remember that, especially with
wooden propellers, there is a tendency for
the material to shrink, or for it to be
reduced by the serrated face of the drive
hub. Retighten the propeller nut if
necessary after loosening the Safety
Propeller Locknut. The locknut should be
tightened firmly after retightening the
propeller nut.
NOTE:
21
Since the compatibility of the
glowplug and fuel may have a
marked effect on performance and
reliability, it is suggested to use the
O.S. Type F plug when it is
necessary to replace.
Carefully install plug finger-tight,
before final tightening with the
correct size plug wrench.
GLOWPLUG
The role of the glowplug
Glowplug life
Particularly in the case of very high performance
engines, glowplugs must be regarded as expendable
items. However, plug life can be extended and engine
performance maintained by careful use, i.e.:
Install a plug suitable for the engine.
Use fuel containing a moderate percentage of
nitromethane unless more is essential for racing events.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
With a glowplug engine, ignition is initiated by the
application of a 1.5-volt power source. When the
battery is disconnected, the heat retained within the
combustion chamber remains sufficient to keep the
plug filament glowing, thereby continuing to keep the
engine running. Ignition timing is 'automatic' : under
reduced load, allowing higher rpm, the plug becomes
hotter and, appropriately, fires the fuel/air charge
earlier; conversely, at reduced rpm, the plug become
cooler and ignition is retarded.
Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:
When to replace the glowplug
Filament surface has roughened and turned white.
Filament coil has become distorted.
Foreign matter has adhered to filament or plug
body has corroded.
Engine tends to cut out when idling.
Starting qualities deteriorate.
