MAINTE}dANCE
OF
E,NGINE
1.
DISMANTLING
OF'
ENGINE.
(a) Decarbonlsing.
Remove
H.T.
Iead.
Remove
sparking
plug. Remove
petrol
pipe
by
unscrewing
the carburetter
banjo.
Remove
cowl
by unscrewing
top
bolts,
washers
and base
nuts.
Detach
throttle
link from
bottom
joint.
Remove
nuts
and bolts
holding
down
cylinder
head'
Lift
off
cylinder
head.
Remove
gasket.
Norri.-When
replacing
gasket,
see
that this
is replaced the
correct
way,
i.e.,
to conform
to
inside shape
of
cylinder
head,
and not
overlapping
on one side.
Take
off inlet
pipe
with
the
Carburetter.
Remove
cylinder
base
nuts and
remove
cylinder,
tal<ing
care
to draw
cylinder
off evenly,
and that
in removal,
piston
does
not foul
side
of connecting
rod.
Remove
valve cover
by
unscrewing
fixing bolt.
Hold
valve down
on
seat,
press
up spring
collar
and
remove cotter.
NorB.-It
is advisable
to
mark
the valves,
so that
they
are
ground
on
their
correct seatings'
Clean
carbon
deposit
from
valves,
valve
ports
and cylinder
head. AIso
remoYe carbon
deposit
from
pistou
crown
and clean,
taking
great
care not to
scratch,
or otherwise
damage
the surface.
Apply
a small
quantity of fine
carborundum
paste to
ttre
valve
seat and
place in
position
for
"
grinding in."
Twist
valve
in a
semi-rotary
motion,
using
a
very light
pressure,
for
a short
while,
occasionally
lifting
valve
and turning
to
a
fresh
position.
Remove
valve
and wipe
face
and seat clean'
Thoroughly
wash
with
clean
paraffrn and
dry. Replace
valve
and
turn
on seating
a few
times.
Withdraw
and see
if both
valve
and
seat show
a bright
line
all
round.
If not, repeat
the
process until
this
result
is
obtained.
Mal<e
sure
that
valves
and their
component
parts are
replaced
correctly.
Replace
cylinder
on engine
and
check clearances
between
tappet
head
and
valve
stem. For
correct
clearances
see Pages
Nos.
4
to
'l
,
and
method
of obtaining
them,
see
valve
gear,
Page 12,
paragraph
(a).
(b) Ptston.
Inspect
piston rlngs
and see
that
they
are
{ree to
move
in
thelr
respective
€(rooves,
that they
are not worn,
cracked,
or broken.
Inspect
piston ring
groove.s
and carefully
clean
if
necessary.
Also
see that
oil drain
holes
in
pistorl are
dear.
Prcn
l0
To remove
piston
from connecting rod, first remove circlip as
{oliows: Insert a sharp
pointed
tool, such
as
a scriber or similar
tool, into one end of the transverse slots in
gudgeon
pin
boss and
under tail of circlip. Lever circlip
frorn its groove, holding
a
piece
of
rag
in front to
prevent
circlip
flying
out
and
causing any
personal
injury.
Push
out the gudgeon
pin
in the direction of removed circlip.
Lift
piston
clear
of connecting rod.
Remoual
ønd
Replacentent
af
Pistun
Rings.
To
remove piston rings
from their
grooves,
a piston ring expanrling
tool may be used. If this
is
not
available, obtain
several thin and
narrow
strips
of metal and insert
these
betrveen back of
piston
rinp
and piston.
Work
these strips round until all rings stand clear of
their
respective
grooves.
The
rings
may now be easily removed
by sliding in an upward direction,
clear of piston. If rings are
serviceable, or
if a new ring or rings are fitted, reverse the
proce-
dure of
removal.
(c) Blg
and Small Ende.
The small-end bush
is a
press
fit
in
the connecting rod
and
is reamed
to size after fitting to connecting rod.
It
may be
removed
by using
a special drawbolt or by
pressing out
with
hydraulic
or
hand
press.
Reverse the above
procedure
when
f,tting new bush.
The
big-end
is
steel
backed. The
2 halves of
bearing
are
secured
in working position by bolts and self-locking
nuts.
(d)
Matn
Bearlnge.
The main bearings
are
situated
on either end
of
crankshaft. The
centre
portions, which
carry the rollers and cages
are
a
press
fit
on crankshaft
journals.
The outer
races
are carried
in housing plates on either end
of
cran-k-
case and
are a
press
fit.
Noru.-The
centre
portion
of
main bearings
are not easily removable
from crankshaft
journals,
and should not be
removed
unless re-
placement is necessary.
(e)
Crankshaft.
To remove
crankshaft from crankcase proceed as follows: Remove
frorn
driving end
of crankshaft any coupling device,
also its key.
Withdraw splitpin from
starting pin and knock out starting
pin.
Unscrew bolts
and remove starting
boss.
Next
remove flywheel
securing nut.
lteplace starting
boss and fixing screws.
Screw
the
special
draw
bolt into centre of starting boss
and
continue
to screw
in
until flywheel is free
on taper,
taking
care not to lose the key.
Remove
flywheel
clear of craakshaft. Now
remove nuts holding
Pecr I 1
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