1A-4 - GENERAL INFORMATION
90-823224--2 796
Engine Serial Number
Locations
72923
b
a
Stern Drive (MCM)
a - Serial Number Plate
b - Starter Motor
72924
b
a
Inboard (MIE)
a - Serial Number Plate
b - Starter Motor
Propeller Information
Refer to the “Propeller” section in appropriate Mer-
Cruiser Stern Drive Service Manual, or order publica-
tion 90-86144-92, “Everything you need to know
about propellers.”
Changing diameter, pitch or coupling of a propeller
will affect engine RPM and boat performance. The
blade configuration also will affect performance. Two
like propellers, same pitch and diameter, from two dif-
ferent manufacturers also will perform differently.
It is the responsibility of the boat manufacturer and/or
selling dealer to equip the boat with the correct pro-
peller to allow the engine to operate within its speci-
fied RPM range at wide-open-throttle (W.O.T.).
Because of the many variables of boat design and
operation, only testing will determine the best propel-
ler for the particular application.
To test for correct propeller, operate boat (with an av-
erage load onboard) at W.O.T. and check RPM with
an accurate tachometer. Engine RPM should be near
top of the specified range so that, under heavy load,
engine speed will not fall below specifications.
If engine exceeds the specified RPM, an increase in
pitch and/or diameter is required.
If engine is below rated RPM, a decrease in pitch
and/or diameter is required.
Normally, a change of approximately 150 RPM will be
achieved for each single inch of pitch change of a
propeller.
!
CAUTION
If a propeller is installed that does not allow en-
gine RPM to reach the specified full-throttle RPM
range, the engine will “labor” and will not pro-
duce full power. Operation under this condition
will cause excessive fuel consumption, engine
overheating and possible piston damage (due to
detonation). On the other hand, installation of a
propeller, that allows engine to run above the
specified
RPM limit, will cause excessive wear on
internal engine parts which will lead to premature
engine failure.
Water Testing New Engines
Use care during the first 20 hours of operation on new
MerCruiser engines or possible engine failure may
occur. If a new engine has to be water-tested at full
throttle before the break-in period is complete, follow
this procedure.
