Service Manual
6-2
COMPRESSION
CYLINDER HEAD CHECK
AND REPAl
R
1.
Clean cyl. head.
WARNING: Be
alert
to fire if combustible
cleaner
is
used.
2.
Check cyl. head flatness by placing cyl. head
on
a
surface plate more than
at
six points.
3.
Use
a
thickness gauge
(A)
to measure the
space between surface plate and cyl. head.
Cyl.
Head Warp (MAX)
0.4
mm
(0.01
5 in.)
I
I
J
4.
If cyl. head
is
warped more than specified,
replace
it.
5.
If cyl. head
is
warped
less
than the specified
limit, reface the head surface by rubbing on
emery paper (first:
No. 200,
then: No. 400)
placed on
a
surface plate.
6.
Check cyl. head gasket for burn and trace of
gas
leakage. Replace gasket if necessary.
VALVE AND SPRING REMOVAL
1.
To remove
valves
using
a
valve spring com-
pressor
(A),
put screw head of compressor
over the
valve
head and slip lower jaw between
spring
(B)
and retainer
(C).
2.
Compress spring. Remove retainer by
a
needle
nose plier. Pull out
valve.
Remove compres-
sor and
valve
spring.
VALVE SPRING INSPECTION
1.
Inspect
valve
springs for damage. Replace
2.
Measure the free length of springs. If shorter
springs if necessary.
than specified, replace spring.
Valve Spring Free Length
(MIN)
Intake
I
43.3
mm
(1.705 in.)
Exhaust 39.0
mm
(1.535 in.)
TO
ANALYZE VALVE
When leaded gasoline
is
used,
excessive
lead
deposits on the exhaust
valve
are caused by
exhaust
gas
leakage past the
valve.
This in-
dicates the
valve
is
not seating properly.
Clean the seating face and lap the valve into
the
seat.
If worn severly, grind the
valve
and
reface the
seat
to correct condition.
CAUTION: Be sure to reset valve-to-tappet
clear-
ance after grinding
valve.
Valve stem corrosion
is
caused by moisture
in the engine. Moisture in the fuel-air mixture
or combustion
gases
can condense inside the
engine when the engine
is
stopped and cools
down.
Valve corrosion can also occur during storage.
Fogging or pouring oil in combustion chamber
before storing helps prevent
valve
corrosion.
Corroded or pitted
valves
collect deposits
and may cause sticking
valves.
Replace badly corroded or pitted
valves.
Poor engine cooling due to dirt or obstructions
is
a
common cause for overheating an engine
and the
valves.
Remove flywheel housing and
clean cooling fins.
Other causes for
valves
running hot are worn
valve guides or
valve
springs, incorrect
valve
clearance, lean fuel-air mixture and incorrect
or overheated plug.
Use of old or stale gasoline
is
a
common cause
for sticky
valves.
This gummy deposit can
be seen on the
valve.
When this condition
exists, the carburetor may also contain gum
deposits and will require
a
complete cleaning.
CAUTION: Always use fresh gasoline and drain
fuel tank, lines and carburetor before storing
equipment.
VALVE INSPECTION
1.
Remove carbon from
valve
head, face and
stem with
a
power-operated wire brush.
Be
sure carbon
is
removed and not merely burnish-
ed.