BOMBARDIER SEA-DOO GS 5626 1998, Руководство по ремонту

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Section 04 ENGINE
Subsection 05 (TOP END)
04-05-4
GENERAL
The 2-stroke ROTAX engine rotates counterclock-
wise seen from the rear (PTO flywheel).
The 717 and 787 engines have a rotary valve to
control opening and closing of the intake. The 947
engine uses reed valves in the crankcase.
The 787 and 947 engines are also equipped with
the RAVE system (Rotax Adjustable Variable Ex-
haust).
787 and 947 Engines
These engines are canted at a 30 degree angle
(they are not canted on the same side), lowering
the center of gravity of the watercraft. Cylinder
exhaust ports are located on the same side of the
intake, allowing a high volume tuned pipe design.
RAVE System
THEORY
For a 2-stroke-cycle engine to have high power ca-
pacity at high crankshaft speeds, a high volumet-
ric or breathing efficiency is required and the fresh
charge losses must be minimized. The result is
achieved by opening the exhaust port early and
utilizing the resonant effects of the tuned exhaust
system to control fresh charge losses.
When an engine of this design is run at a medium
speed, efficiency falls off quickly. The relatively
high exhaust port effectively shortens the useful
power stroke and because the exhaust system is
tuned for maximum power, there is a large in-
crease of fresh charge losses. As a result, the
torque decreases along with a dramatic increase
of the specific fuel consumption. Higher torque
along with lower fuel consumption can be ob-
tained at lower engine speeds if the time the ex-
haust port is open is shortened.
BOMBARDIER-ROTAX has patented a remark-
ably simple system to automatically change the
exhaust port height based on pressure in the ex-
haust system (and RPM for the 947 engine).
Located above the exhaust port is a guillotine-
type slide valve. This rectangular valve is connect-
ed by a shaft to a diaphragm which is working
against the return spring.
To the outside of the return spring is a red plastic
adjustment knob. Turning the adjustment in or out
changes the preload on the return spring which, in
turn, will change the RPM at which the RAVE
valve opens and closes.
787 Engine
One small passage in the cylinder just outside the
exhaust port allows exhaust gas pressure to
reach the diaphragm.
TYPICAL
1. Sliding valve
2. Diaphragm
3. Spring
4. Exhaust port
5. Adjustment knob
As the throttle is opened and the engine begins
producing more power, the pressure against the
diaphragm will overcome the pressure of the re-
turn spring and the RAVE valve will open.
VALVE FULLY OPENED
-
CAUTION
No engine components can be interchanged
between engines.
A18C01A
1 5
3
2
4
F01D7GA