BOMBARDIER SEA-DOO GS 5626 1998, Shop Manual

Page: 83 / 426

Section 04 ENGINE
Subsection 05 (TOP END)
04-05-8
787 and 947 Engines
The RAVE valve does not allow an engine to make
higher peak horsepower than an engine not so
equipped, it can make moving the peak horse-
power higher practical because of its effect on the
rest of the power curve. Item 2 in the following
figure is the power curve of an engine with the
RAVE valve held fully open through its entire RPM
range. Item 6 notes the peak power produced.
That peak will not change if the exhaust port time
of a similar engine without a RAVE valve was the
same (with all other features equal).
Item 1 is the power curve of the engine with the
RAVE valve closed through its entire RPM range.
The shaded area (item 3) is the improvement in
power at lower engine speeds that is gained be-
cause of the lower exhaust port. If the port re-
mains at this height, however, the power would
peak as noted in item 5. Raising the exhaust port
at the proper RPM (item 7) will allow the engine
peak power to continue to rise (item 6).
Item P1 in figure is the force of the return spring
against the diaphragm. The exhaust pressure
must be high enough to overcome this force be-
fore the valve begins opening. Item P2 is the pres-
sure required to completely open the RAVE valve.
Between P1 and P2, the usable power curve of
the engine is moving from power curve 1 to pow-
er curve 2. This transition takes place very rapidly
at full throttle and from a practical standpoint can
be considered to be instantaneous at item 7.
Gradual application of the throttle, however, will
result in the RAVE valve opening much later.
MAINTENANCE
There are no wear parts anywhere in the system
and there are no adjustments to be periodically
checked. The only possible maintenance required
would be cleaning of carbon deposits from the
guillotine slide. Cleaning intervals would depend
upon the user’s riding style and the quality of the
oil used. Using FORMULA XP-S synthetic injec-
tion oil, we would suggest annual cleaning of the
valve. If a customer uses a lower quality oil, more
frequent cleaning may be required.
No special solvents or cleaners are required when
cleaning the valve.
BORING PRECAUTION
In its stock configuration the RAVE valve guillotine
has a minimum of 0.5 mm (.020 in) clearance to
the cylinder bore measured at the center line of
the cylinder. This is the minimum production
clearance.
There is only a first oversize piston available for
the 787 and 947 engines. That piston is 0.25 mm
(.010 in) larger in diameter than the stock piston.
When the oversize is installed, the guillotine will
have a minimum clearance of 0.375 mm (.015 in)
with the cylinder bore. This is the minimum oper-
ating clearance the guillotine should be used with.
Clearance less than 0.375 mm (.015 in) will re-
quire reworking of the guillotine to achieve the
proper clearance and radius.
DISASSEMBLY
15, RAVE Valve
787 Engine
Remove the cover no. 18 of the valve by releasing
the spring no. 16 .
P1
P2
7
6
4
5
3
1
1
2
POWER
RPM
A18C02A
◆
WARNING
Firmly hold cover to valve base. The spring in-
side the valve is applying a pressure against
the cover.