O.S. Engines FL-70 - Manual (Page 12)

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PROPELLER & SPINNER ATTACHMENT
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.
Lock Nut
Propeller Washer
Propeller Nut
Ream the propeller shaft hole to 6.4-6.5mm
bore with an appropriate reamer, checking
that the hole is exactly centered. 1.
Install the prop to the engine shaft, followed
by retaining washer and prop nut lightly.
Turn the prop counter-clockwise slowly to
locate the position where compression is
felt. At this position, fit the prop horizontally
and tighten firmly the prop nut with a 13mm
wrench. 2.
Add the specially tapered and slotted
locknut and secure with a 10mm wrench
while holding the prop nut with the 13mm
wrench. 3.
Fit a spinner assembly to start the engine
with an electric starter. 4.
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Note:
Some spinners which are fixed at the top of
the cone cannot be used with the prop
locknut supplied with the engine. In this
case, optional locknut sets are available
from O.S. – Propeller Locknut Set for
Spinner (Code No.45810200) and Propeller
Locknut Set for Tru Turn Spinner (Code
No.l45810300).
IMPORTANT
Regardless of the type of propeller used,
make a habit of always checking the
tightness 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.