Evinrude 4906B 4HP 1969 Owner's Manual page 52

During a normal
covers should be removed, cleaned, and new
gaskets installed.
ensure installation
from which they are removed.
INSTALLATION
Procedures to install the bypass covers
to the powerhead will be found in Section 3-
15, Cylinder Block Service,
Cover and Exhaust Cover Installation.
3-7 EXHAUST COVER
The exhaust covers are one of the most
neglected items on any outboard
Seldom are they
Many times an engine may be overhauled
and returned to service without the exhaust
covers ever having been removed.
One reason the exhaust covers are not
removed is because the attaching
ually become corroded in place.
they are very defficult
work should be done.
bolt head and around the exhaust cover will
help in removal. However, some bolts may
still be broken. If the bolt is broken it must
be drilled out and the hole tapped with new
threads.
The exhaust covers are installed over the
exhaust ports to allow the exhaust to leave
Removing the exhaust cover from the powerhead.
overhaul, the bypass
Identify the covers to
in the same location
under Bypass
engine.
checked and serviced.
bolts us-
This means
to remove, but the
Heat applied to the
BYPASS
the powerhead and be transferred
exhaust housing. If the cover was the only
item over the exhaust
become so hot from the exhaust gases they
might cause a fire or a person would be
severely burned if they came
with the cover.
Therefore, an inner plate is installed
help dissipate the exhaust heat.
kets are installed -- one on either
the inner plate. Water
circulate between the exhaust cover and the
inner plate. This circulating water cools the
exhaust cover and prevents it from becom-
ing a hazard.
On some early model outboards (the late
1950's and early 1960's), the inner plate was
constructed of aluminum.
the aluminum would corrode through, espec-
ially in a salt water enviroment,
water could enter
cause a power head failure.
ing illustration clearly shows an inner plate
corroded through, allowing water to enter
the lower cylinder.
sion problem, the inner plate is now made of
stainless steel material.
A thorough cleaning of the inner plate
behind the exhaust
formed during a major engine overhaul.
the integrity of the exhaust cover assembly
is in doubt, replace
including the inner plate.
Removing the inner plate from the powerhead.
COVERS
to the
ports, they would
in contact
Two gas-
side of
is channeled
Unfortunately,
and then
the lower cylinder
The accompany-
To correct this corro-
covers should be per-
the complete cover
3-11
to
to
and
If