O.S. Engines FS-91 II FI - Manual (Page 13)

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Install the EC-2 in a location that is not susceptible to the effects of heat, fuel or vibrations while
allowing easy manipulation. Always make sure to attach double-sided, sponge-backed cushioning
tape or Velcro tape between the airframe and EC-2 as measures against vibrations.
(4) EC-2
Fit these in the following sequence.
Screw the header pipe into the cylinder head until it " bottoms ", then unscrew sufficiently to achieve
the desired exhaust angle and tighten the locknut securely with a 14mm wrench. Screw the silencer
onto the outer end of the header pipe and tighten the other locknut.
The application of a heatproof silicone sealant to the threads of the exhaust system is recommended
to reduce the risk of joints loosening and the leakage of exhaust gases and oil residue.
Reminder:
Model engines generate considerable heat and contact with the header pipe or silencer may
result in a serious burn.
If you need to tighten the silencer joints, which may loosen when they are hot, use a thick
folded cloth for protection.
(5) EXHAUST HEADER PIPE & SILENCER
Since the engine is intended to be started with an electric starter, the addition of a
spinner assembly for centering the starter sleeve is desirable. Special propeller locknut
set (Code No. 45910300) is available as optional extra for use with spinners.
(6) PROPELLER & SPINNER ATTACHMENT
Ream the propeller shaft hole to 8.1mm bore with an appropriate
reamer, checking that the hole is exactly centered.
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.
Fit this as follows:
Lock Nut
Propeller Washer
Propeller Nut
1.
2.
3. Add the special tapered and slotted locknut and secure with a
12mm wrench while holding the prop nut with the 14mm
wrench.
Fit the prop to the engine shaft, followed by the retaining washer
and prop nut and tighten firmly with a 14mm wrench.
Fig.7