Valve Timing Marks - BSA B31 Instruction Manual

should
be
st€adied
to
prevent possible damage.
Whetr
the
barrel is remov€d,
cover
the
mouth of the
craokcåse
with
rag
to
prevent rust and
gdt falling
in.
To
reftove the
piston
from
the connecting
rod
it
is first
necessary
to take
out
one
of the gudgeon
pin circlips.
This is best ac.om-
plished with
a pointed
instrument
such as
the tang
of
a
file suitably ground.
Before
the
gudgeon
pin
can be withdrawn
it
may
be
necessary,
jf
the engine is
cold, to
heat the
piston
with the
aid of
rags
imme6ed
in
hot water, wrung
out,
and held
round
tlle
piston. Then, supporting the piston,
tap tbe
gudgeon
pin
through using
a light hammer and
a
punch.
When the piston
is free,
mark
the inside
of the piston
skfut
at th6 back, so that
it
can be replaced the
corect
way
rouod.
If
the rings are stuck
in
the
grooves
gleat
care
will
be
treeded
to pdse them free and
to
lemove them
from
the
piston. All
carbon deposit
should be carefully
scraped
from the
grooves
and the inside
edges
of
the
rings.
If
eithe.
of
the
rings
shows
brown patches
on
the
face,
replace
with
a
new
qg.
Check
the
piston
ng gap by
inserting
the piston in
the
barrel and
sliding
each
ling
indcpendently
up to
the
skiit
ofthe piston, check the gap
with feeler
gauges,
and
this should not
be less
than
.008
in. or
morc than
.012
in.
Fit new rings
if
the
gap
greatly
exoeeds
the figure
stated,
although a few thousandths
of an inch extra gap are not
serious.
It
is
advisable
to
check
the
gap of
new
dngs
before
fitting, and
if
the
gap is
less
than
.008
in,
the ends
of
the
rings should
be
carefully filed to
the
corect
limit.
It
should
be noted
that
piston rings
are
very britde,
and
unless
handled carcfully
a.e easily
broken.
This
appties
palticula
y to
the søaper
ring.
Re€ssembling.
When the lings arc refitted, replace the
piston on
tho connecting
rod (see that
it
is the right way
round),
smeår
the gudgeon
pin libe(ally with
engine
oil,
add tap
into position.
Then
refit
the Sudgeon
pin circ[p.
Smear the
pistor
liberally
witl
clean eDgine
oil;
turn
thc
dngs.
so
that tho gaps are
on
opposite
sides
of
the
pistoo;
fit
a
ncrf,
cylinda!
base washer
on the
cmnkcase;
liberElly
c.at
the inride of
the
cylhder barrel wirh
clean
engine
oil
aDd then, coEplessing the rings
in
tum
by
hand, carefully slide the
baEel
i[to
position over
rhe
piston. This
operation
will
be simplified
if
the piston
rings ar€ compressed into their
grooves by
means
of
metal
bands,
such as can be
obtained
from
accessory suppliers.
Next
replace
the
valves
into
their
respective
positions,
place
the springs over the
stems
with the top collar
iD
porition,
and
with
l,he
head
rsting
on
wooden block
as
befor€, compress
the
springs
until
the split
collets can be
inserted.
A
dab
of
grease on
the
inside of
the
collets
will
serve
to hold
them
in
position u.til
the spring is released.
Make quite
sure
that
the collets are corlectly
located,
(For
Comp.
and Gold
Star models
see
pages
49 and
5l
respectively).
ng.
17.
Valw timing ,narks
Standard
kon
B
engines
or
y.
Insert
the push-rod cover
tube
into position
iD tho
oylinder
head
but do not
screw
up
the gland
nut.
Place
the push-rods inside the tubes
and
then
lift
the
cylinder
head
into position. It
will
be
necessary
to ke€p the
head
raised whilst
the push-rods
are
positioned
on
the tappets, atrd then the rods must be
corectly located
oq
the
rocke$.
Now lorrer
the
head
into
position,
rcplacc
the acom nuts secudn8 the
push-rod
tube, add then screw
up
the long cylinder
head
and barrel bolts, working
in
diagonal
orde!
until
they are deåd
tight.
The push-rod
gland
Dut can
dow
be
tightened
up.
Before replacing the
inspection and tappet
covers, check
tappet
adjustments.
which should give
.@3
in.
clearance
at
both
valves.
i
I
ij
I
I
I