O.S. Engines 91SX-H - Manual (Page 7)

Because of initial tightness, a
standard electric starter may have
difficulty in rotating the engine when
cold, before it has been adequately
run-in. In this case, use a high-torque
type starter.
DO NOT, however, confuse tightness
with the symptoms of hydraulic lock
caused by an excess of fuel within the
cylinder - often the result of over-
priming.
Attempting to force the engine to turn
over in this condition may cause
internal damage. Instead, remove the
glowplug, invert the engine and eject
surplus fuel from the combustion-
chamber.
Note:
This is a high performance engine
developed to meet the new F3C
helicopter competition regulations that
allows 15cc engine capacity.
The engine uses the same mounting hole
spacing as the O.S. 61SX-H RING WC as
well as the 61LX-H RING making them
interchangeable. However, higher gear
ration is required for the 91SX-H RING
which generate maximum power at lower
rpm than the 61 size engines.
Easier to adjust single needle type 60L
carburetor is employed. A special
machined drive washer and dual throttle
washer are supplied as standard for
helicopter use.
INTRODUCTION
6