3
POWERHEAD
3-1
INTRODUCTION
The carburetion
and ignition
principles
of two-cycle
engine operation
MUST
be un-
derstood
in order to perform
a proper tune-
up on an outboard
motor.
Therefore,
it
would be well worth
the time
to study the
principles
of two-cycle
engines
as outlined
in this section.
A Polaroid,
or
equivalent
instant-type
camera,
is an extremely
useful item provid-
ing the
means
of accurately
recording
the
arrangement
of parts
and wire
connections
BEFORE
the disassembly
work begins.
Such
a record is most valuable
during the assemb-
ly work.
Tags
are
handy
to identify
wires
after
they are disconnected
to ensure they will be
connected
to the same terminal
from which
they were removed.
These tags may also be
used for parts
where marks or other
means
of identification
are not possible.
THEORY OF OPERA nON
The two-cycle
engine
differs
in several
ways from a conventional
four-cycle
(auto-
mobile) engine.
1-
The
method
by which
the
fuel-air
mixture
is delivered
to the
combustion
chamber.
2-
The complete
lubrication
system.
3- In most cases, the ignition system.
4-
The frequency
of the power stroke.
These differences
will be discussed
briefly
and compared
with four-cycle
engine opera-
tion.
Intake/Exhaust
Two-cycle
engines
utilize
an
arrange-
ment of port
openings
to admit
fuel to the
combustion
chamber
and to purge
the
ex-
haust
gases
after
burning
has
been
com-
pleted.
The ports
are located
in a precise
pattern
in order
for
them
to be open
and
closed off at an exact
moment
by the piston
as it moves
up and down in the
cylinder.
The exhaust
port
is located
slightly
higher
than the fuel intake
port.
This arrangement
opens the
exhaust
port
first,
as the
piston
starts
downward, and therefore,
the exhaust
phase
begins
a fraction
of a second
before
the intake phase.
Actually,
the
intake
and exhaust
ports
are
spaced
so closely
together
that
both
open almost
simultaneously.
For this
rea-
son, the pistons
of most
two-cycle
engines
have
a deflector-type
top.
This design
of
the
piston
top
serves
two
purposes
very
effectively.
DEFLECTOR
EXHAUST
PORT
EXHAUST
Drawing
to depict
the intake
and exhaust cycles
of a
two-cycle
engine.
Summary of Contents for 4906B 4HP 1969
Page 5: ......
Page 87: ...3 46 POWERHEAD Exploded drawing of a 7 5 hp powerhead 1956 58 with principle parts identified...
Page 88: ...CYLINDER BLOCK 3 47 HEAD GASKET RING...
Page 90: ...CYLINDER BLOCK 3 49 THERMOSTAT EXHAUST COVER The...
Page 137: ...4 46 FUEL LEVER AND LOW SPEED...
Page 153: ...4 62 FUEL Exploded view of a pressure tyoe fuel tank with major parts identified...
Page 157: ...4 66 fUEL...
Page 412: ...A 16 APPENDIX Wire Identification 33 hp with Generator 1965 67...
Page 413: ...APPENDIX A 17 o C...
Page 414: ...Wire Identification 33 hp with Generator 1969 70...
Page 415: ...APPENDIX A 19 Wire Identification 35 hp 1957 59...
Page 416: ...A 20 APPENDIX Wire Identification 40 hp Standard Shift with Generator 1960 66...
Page 417: ...APPENDIX A 21 UJ cc b Wire Identification 40 hp Standard Shift with Generator 1967 68...
Page 419: ...APPENDIX Wire Identification 40 hp Electric Shift with Generator 1961 66 A 23...
Page 420: ...A 24 APPENDIX C 00 Wire Identification 40 hp Electric Shift with Generator 1967 68...
Page 421: ...Wire Identification 40 hp Electric Shift with Generator 1969 70...
Page 422: ...NOTES NUMBERS...
