Page 51
Pistons, connecting rods and cylinder bores 212-1
To replace pistons, piston rings
and big-endbearings ........ 212-1 and bores
Classification of pistons
Pistons, connectingrods and cylinder bores
2 @-
\
anus
6,
é Le
t
To renew pistons, piston rings
and big-end bearings
(Engine mounted in workstand, cylinder head re-
moved)
Saab 900
Page 52
212-2 Pistons, connecting rods and cylinder bores
\ To remove
1 Remove any burrs or carbon deposits from
the tops of the cylinders.
2 Remove the big-end bearing caps.
3 Fit the protective sleeves on the connecting
rod studs, Push the pistons and the connect-
ing rods out of the cylinder bores.
To ensure that the parts are refitted in their
original positions, note the markings on the
pistons and con necting rods, put the bear-
ing shells and caps back in position on the
respective con rods and keep each set sepa-
rately.
For measurement of bearing clearance, see sec-
tion 216.
Matching the pistons to the bores
To match pistons to the cylinder bores, use a
feeler gauge, 1/2-in wide. To measure, first oil
the bore lightly and insert the piston without
rings in the bore in which it will be working. At-
tach the feeler gauge to a spring balance and in-
sert it between the piston and cylinder bore at
right angles to the axis of the gudgeon pin. Ata
tractive force of 8-12 N (1.7 - 2.6 Ibf), the mean
value of the clearance equals the thickness of
the feeler gauge.
Saab 900
——
Page 53
ie Aeaieecncaaalel MMMM Ie ea:
' Pistons, connecting rods and cylinder bores 212-3
Repeat the test with the piston at several diffe- | ]
rent depths. For piston clearances, see the |
‘Technical data’ section. il
Spare pistons are stocked in both standard and
oversize diameters. Where the latter are used,
the cylinder bore must be honed or rebored to ob-
tain the correct piston clearance. |
Carry out the matching as follows:
Using a feeler gauge and spring balance, deter-
mine which piston (or pistons) has abnormally
large clearance. Replace the piston (or pistons)
with a piston {or pistons) of the next oversize.
Check the piston clearance of the new piston (or
pistons), using the feeler gauge and spring ba-
lance.
Example of class A cylinder and class A piston
When the piston clearances are measured in the
engine by means of a 0.05-mm (0.002-in) feeler
gauge, no measurable force is recorded on the
spring balance when withdrawing the feeler
gauge from no. 2 and no. 3 cylinders.
Inno. 1 and no. 4 cylinders, the pistons cannot
be fitted into the cylinder bores with a 0.05-mm
(0.002-in) or 0.04-mm (0.0016-in) feeler
gauge. When the piston is inserted with a
0.03-mm (0.0012-in) feelier gauge, the force
necessary to pull out the feeler gauge is 20N
(4.4 |bf) and, with a0.02-mm (0.0008-in) feeler
gauge, GN (1.3 bf}. The piston clearance in no.
1 and 4 cylinders is therefore estimated to be
0.032 mm, (0.0013in), and the pistons in these
cylinders need not be replaced. }
Since the piston clearance in no. 2 and no, 3 ; i
cylinders is greater than 0.05mm (0.002 in), it
is estimated that the diameter in these bores at \
maximum tolerance is 90.010 mm (3,5437 in); f|
allowing a further +0.003mm (0.0001 in) for i
bedding-in, this gives a bore of 90.013mm \)
(3.5438 in).
Saab 900 i i i
Page 54
212-4 Pistons, connecting rods and cylinder bores
Assume a standard B piston.
The theoretical piston clearance will then be
0.009-0.017mm (0.0004- 0.0007 in). Allow-
ing a further 0.02mm (0.0008 in) for bedding-
in, this gives a maximum clearance of 0.037 mm
(0.0015 in), which should be sufficient to elimi-
nate unacceptable piston slap. Choose standard
B pistons for these bores and check with a feeler
gauge
N.B.
Pistons of different makes must not be used in
the same engine. The name of the piston manu-
facturer is cast-in on the inside of the piston, Pis-
tons of the following makes are fitted in produc-
tion:
Mahle
Karl Schmidt
Hepolite
The weight difference between the various pis-
ton classes is negligible.
Classification of Pistons and
cylinder bores
The piston class is stamped on the piston crown.
The piston classes for service are:
AB
B
C
The cylinder class is stamped on the cylinder
plane and is specified for each cylinder.
The cylinder class may be A or B, and both clas-
sSeés may occur in any cylinder block.
Classification of pistons
See "Technical data”.
Cylinder block
See "Technical data”.
Resulting piston clearances
See "Technical data”.
Page 55
istons, connecting rods and cylinder bores 212-5
Matching piston rings to a new or re-
bored cylinder
1 Push the piston rings down into the cylinder
one ata time, using an inverted piston head
to position them correctly.
2 Measure the ring gap with a feeler gauge, as
shown. Correct gap sizes are given in the
‘Technical data’ section. If necessary, widen
the gap with a special file.
3 Try the piston rings in their respective
grooves by rolling. Measure the clearance at
a few points too.
Fitting piston rings In a worn cylinder
a
Rings to be fitted in a worn cylinder must be tried
at the lower limit of travel of the piston (BDC), as
the bore is narrowest at this point.
To fit piston rings to pistons
Use the piston ring clamp (special tool) to fit the
rings as shown. The lower compression ring must
be fitted with the side marked “TOP” uppermost.
Oil the piston and rings before assembly.
Saab 900 {
Page 56
EE
| 212-6 Pistons, connecting rods and cylinder bores
Position the compression rings so that the gaps
Piston and connecting rod with bearings and Dis-
ton rings
1 Piston
2 Connecting rod
3 Bearing
4 Bearing cap
5 Compression rings
6 Oil scraper ring
are at approx. 180° to each other, each
positioned above one of the gudgeon pin holes.
Make sure, that the gaps in the oil scraper ring
are equally spaced out round the piston, and not 1
in line with one another.
$7871
1 Compression rings
2 Scraper ring
To fit the pistons in the bores
1 Place the bearing shells in position in the
connecting rods and fit protective sleeves to
the connecting rod studs.
2 Oil the piston rings and bearings.
Saab 900
Page 57
Pistons, connecting rods and cylinder bores 212-7
3 Refit the pistons using piston ring compres-
sor 7862 287.
Ensure that the notch in the piston crown
points towards the timing cover and that the
numbers on the connecting rod face the
exhaust side.
$7038 ii
4 Refit the big-end bearing caps with bearing
shells (the big-end bearing and big-end
bearing cap identifying numbers should
coincide). The big-end bearing nuts should
be fitted with the flanges towards the con-
necting rods.
Saab 900
Page 58
212-8 Pistons, connecting rods and cylinder bores
: i Tightening torque big-end bearings 55 Nm
(40 Ibf ft).
na
Saab 900
Page 59
tee
214-16 Valve gear, B201 and B202
Valve gear, B202
General
The valve gear incorporates hydraulic cam fol-
lowers, which keep the valve clearance within a
limited working range of 2.05mm (0.081 in).
This range lies between 18.75 and 20.8mm
(0.738 -0.819 in) from the camshaft to the end
of the valve stem.
Each cam follower has two storage chambers
and one high-pressure chamber. The opening of
the port between the high-pressure chamber and
the adjacent storage chamber is controlled by a
spring-loaded ball valve. A return spring in the
high-pressure chamber acts on the sliding pis-
ton, to eliminate any clearance between the cam
follower and the cam. At the same time, the high-
pressure chamber expands and makes up the oil
volume, to compensate for leakage losses oc-
curring at actuating pressure in the passage be-
tween the piston and the cylinder.
The hydraulic cam followers are sealed units; if
defective, they cannot be repaired but must be
replaced. Under various conditions, the hyd-
raulic cam followers may give rise to a tapping or
chattering noise. In most cases, the noise will be
short-lived and remedial action will not required.
The following list details the commonest times
that chatter is likely to be heard and what initial
action, if any, should be taken to eradicate it.
1 Valve chatter on starting the engine after an
oil change.
If the noise from the valves did not occur be-
fore the oil change, the noise wil! disappear
of its own accord as soon as the oil in the en-
gine has reached normal working pressure.
Oi! flow through the cam follower
oOfhWhNoP
2/352
Storage chamber
Leakage passage
Check valve
High-pressure chamber
Spring
Saab 900
Page 60
Valve gear, B201 and B202 214-17
2 Initial noise on starting a cold engine.
This noise is perfectly normal and will disap-
pear of its own accord as soon as the oil in
the engine has reached normal working
pressure.
Valve chatter on starting after work on the
car that has involved cranking the engine by
hand or on the starter motor.
The noise is due to one or more of the cam
followers having been drained of oil and will
therefore disappear after the engine has
been running for a while. At worst, it may
take fifteen minutes at between 2000 and
3000rpm for the noise to disappear. At
lower engine speeds, it will obviously take
considerably longer to expel the air. Do not
run the engine at a speed greater than
3000 rpm as this may damage the cam fol-
lowers.
Noise after fitting new cam followers.
Same cause as item 3 above.
Noise occurring after a short period of idling
with a hot engine (hot oil).
lf the engine is run at 1500 rpm or more, the
noise will disappear after a while.
The noise is due to low oil pressure in the
hydraulic cam followers when the engine is
idling. Check the oil feed pipe, connectors
and 'O’ rings for leaks.
Noise occurring at high engine speeds and
disappearing after the engine has been left
idling for some time.
This noise is due to an excessive amount of
air in the oil at high engine speeds. The in-
gress of air is caused by leakage on the suc-
tion side of the oil pump, a poorly sealing
‘O' ring in the suction pipe or a leak in the
suction pipe caused, for instance, by a por-
ous weld.
Noise from an individual cam follower re-
gardless of how the car is being driven.
The most likely cause is that a particle of dirt
has become trapped .in the check valve for
the cam follower. Fita new cam follower. The
defective cam follower (or followers) can be
identified most readily by switching off the
engine, removing the valve cover and using
a screwdriver to depress the cam followers
while they are at rest. If the follower feels
light or spongy, it is defective.
Fa
Saab 900 ‘7