SAAB 9000. Instruction - page 18

2B•18 Engine removal and general overhaul procedures

12.7 Cleaning a cylinder head bolt hole in

the cylinder block using a tap

12.12c Piston classification on the piston

crown

be sure to clean all oil holes and galleries very
thoroughly, and to dry all components well. On
completion, protect the cylinder bores as
described above, to prevent rusting.
7 All threaded holes must be clean, to ensure
accurate torque readings during reassembly.
To clean the threads, run the correct-size tap
into each of the holes to remove rust,
corrosion, thread sealant or sludge, and to
restore damaged threads (see illustration). If
possible, use compressed air to clear the
holes of debris produced by this operation.

12.12a Piston and cylinder bore

classification code locations

Warning: Wear eye protection
when cleaning out these holes in

this way!

8 Apply suitable sealant to the new oil gallery
plugs, and insert them into the holes in the
block. Tighten them securely. Refit and tighten
the oil jets to the bottom of the crankcase on
B2O4/B234 engines.
9 If the engine is not going to be reassembled
right away, cover it with a large plastic bag to
keep it clean; protect all mating surfaces and
the cylinder bores as described above, to
prevent rusting.

Inspection

10 Visually check the cylinder block for
cracks and corrosion. Look for stripped

threads in the threaded holes. If there has

been any history of internal water leakage, it
may be worthwhile having an engine overhaul
specialist check the cylinder block/crankcase
with special equipment. If defects are found,
have them repaired if possible; otherwise, a
new block will be needed.
11 Check each cylinder bore for scuffing and
scoring. Check for signs of a wear ridge at the
top of the cylinder, indicating that the bore is
excessively worn.
12 The cylinder bores and pistons are
matched and classified according to five
codes - AB, B, C, 1 (0.5 mm oversize), and 2
(1.0 mm oversize). The code is stamped on the
piston crowns, and on the front of the cylinder
block (see illustrations). Note that all

12.12b Cylinder bore classification on the

front of the block

classifications may occur in the same cylinder
block.
13 Wear of the cylinder bores and pistons can
be measured by inserting the relevant piston
(without piston rings) in its bore and using a
feeler blade. Make the check with the piston
near the top of its bore. If the clearance is
more than the nominal (new) amount given in
the Specifications, a rebore should be
considered, and the opinion of an engine
reconditioner sought.

1 Before the inspection process can begin,

the piston/connecting rod assemblies must be
cleaned, and the original piston rings removed
from the pistons (see illustration).
2
Carefully expand the old rings over the top
of the pistons. The use of two or three old
feeler blades will be helpful in preventing the

rings dropping into empty grooves (see
illustrations).
Be careful not to scratch the
piston with the ends of the ring. The rings are
brittle, and will snap if they are spread too far.

They're also very sharp - protect your hands
and fingers. Note that the third ring

incorporates an expander. Always remove the
rings from the top of the piston. Keep each set
of rings with its piston, if the old rings are to be
re-used.
3 Scrape away all traces of carbon from the
top of the piston. A hand-held wire brush (or a

13.1 Piston/connecting rod assembly

components

13.2a Removing a piston compression ring

with the aid of a feeler blade

13.2b Removing the oil control ring

A good alternative to
compressed air is to inject
aerosol-applied water-
dispersant lubricant into each

hole, using the long tube usually
supplied.

Engine removal and general overhaul procedures 2B•19

13.13a Prise out the gudgeon pin circlip ...

piece of fine emery cloth) can be used, once

the majority of the deposits have been
scraped away.
4 Remove the carbon from the ring grooves in
the piston, using an old ring. Break the ring in
half to do this (be careful not to cut your
fingers - piston rings are sharp). Be careful to
remove only the carbon deposits - do not
remove any metal, and do not nick or scratch
the sides of the ring grooves.
5 Once the deposits have been removed,
clean the piston/connecting rod assembly with
paraffin or a suitable solvent, and dry
thoroughly. Make sure that the oil return holes
in the ring grooves are clear.
6 If the pistons and cylinder bores are not
damaged or worn excessively, and if the
cylinder block does not need to be rebored,
the original pistons can be refitted. Normal
piston wear shows up as even vertical wear on
the piston thrust surfaces, and slight

looseness of the top ring in its groove.

7 Carefully inspect each piston for cracks
around the skirt, around the gudgeon pin
holes, and at the piston ring "lands" (between
the ring grooves).
8 Look for scoring and scuffing on the piston
skirt, holes in the piston crown, and burned
areas at the edge of the crown. If the skirt is
scored or scuffed, the engine may have been
suffering from overheating, and/or abnormal
combustion which caused excessively high
operating temperatures. The cooling and
lubrication systems should be checked
thoroughly. Scorch marks on the sides of the
pistons show that blow-by has occurred. A
hole in the piston crown, or burned areas at
the edge of the piston crown, indicates that
abnormal combustion (pre-ignition, knocking,
or detonation) has been occurring. If any of the
above problems exist, the causes must be
investigated and corrected, or the damage will
occur again. The causes may include incorrect
ignition timing and/or fuel/air mixture.
9 Corrosion of the piston, in the form of
pitting, indicates that coolant has been leaking
into the combustion chamber and/or the
crankcase. Again, the cause must be
corrected, or the problem may persist in the
rebuilt engine.

13.13b . . . then withdraw the gudgeon pin,

and separate the piston from the

connecting rod

10 Where needed, pistons can be purchased

from a Saab dealer.
11 Examine each connecting rod carefully for
signs of damage, such as cracks around the
big-end and small-end bearings. Check that
the rod is not bent or distorted. Damage is
highly unlikely, unless the engine has been
seized or badly overheated. Detailed checking
of the connecting rod assembly can only be
carried out by a Saab dealer or engine repair
specialist with the necessary equipment.

12 The gudgeon pins are of the floating type,

secured in position by two circlips, and the
pistons and connecting rods can be separated
and reassembled as follows.

13 Using a small flat-bladed screwdriver,
prise out the circlips, and push out the

gudgeon pin (see illustrations). Hand
pressure should be sufficient to remove the

pin. Identify the piston, gudgeon pin and rod

to ensure correct reassembly.
14 Examine the gudgeon pin and connecting
rod small-end bearing for signs of wear or
damage. Wear can be cured by renewing both
the pin and bush. Bush renewal, however, is a
specialist job - press facilities are required,
and the new bush must be reamed accurately.
15 The connecting rods themselves should
not be in need of renewal, unless seizure or
some other major mechanical failure has
occurred. Check the alignment of the
connecting rods visually, and if the rods are
not straight, take them to an engine overhaul
specialist for a more detailed check.
16 Examine all components, and obtain any
new parts from your Saab dealer. If new
pistons are purchased, they will be supplied
complete with gudgeon pins and circlips.
Circlips can also be purchased individually.

17 Position the piston so that the notch on

the edge of the crown faces the timing end of
the engine, and the numbers on the
connecting rod and big-end cap face the
exhaust side of the cylinder block. With the

piston held in your hand and the notch facing

the left, the connecting rod numbering should
face towards you (see illustration). Apply a
smear of clean engine oil to the gudgeon pin.
Slide it into the piston and through the
connecting rod small-end. Check that the

13.17 Relationship of the piston and

connecting rod

piston pivots freely on the rod, then secure the
gudgeon pin in position with the circlips.
Ensure that each circlip is correctly located in
its groove in the piston.
18 Measure the piston diameters, and check

that they are within limits for the
corresponding bore diameters. If the piston-
to-bore clearance is excessive, the block will

have to be rebored, and new pistons and rings

fitted.

19 Examine the mating surfaces of the big-
end caps and connecting rods, to see if they
have ever been filed, in a mistaken attempt to

take up bearing wear. This is extremely

unlikely, but if evident, the offending
connecting rods and caps must be renewed.

Checking crankshaft endfloat

1 If the crankshaft endfloat is to be checked,
this must be done when the crankshaft is still
installed in the cylinder block/crankcase, but is
free to move (see Section 11).
2 Check the endfloat using a dial gauge in
contact with the end of the crankshaft. Push
the crankshaft fully one way, and then zero the
gauge. Push the crankshaft fully the other
way, and check the endfloat (see illustration).

The result can be compared with the specified
amount, and will give an indication as to
whether new thrustwashers are required.

14.2 Using a dial gauge to check the

crankshaft endfloat

2B•20 Engine removal and general overhaul procedures

14.3 Using feeler blades to check the

crankshaft endfloat

3 If a dial gauge is not available, feeler blades
can be used. First push the crankshaft fully
towards the flywheel end of the engine, then
use feeler blades to measure the gap between
the No 3 crankpin web and the centre main
bearing thrustwasher (see illustration).

Inspection

4 Clean the crankshaft using paraffin or a
suitable solvent, and dry it, preferably with
compressed air if available. Be sure to clean
the oil holes with a pipe cleaner or similar

probe, to ensure that they are not obstructed.

Warning: Wear eye protection

when using compressed air!

5 Check the main and big-end bearing
journals for uneven wear, scoring, pitting and
cracking.
6 Big-end bearing wear is accompanied by
distinct metallic knocking when the engine is

running (particularly noticeable when the
engine is pulling from low speed), and some
loss of oil pressure.

7 Main bearing wear is accompanied by
severe engine vibration and rumble - getting

progressively worse as engine speed
increases - and again by loss of oil pressure.

8 Check the bearing journal for roughness by
running a finger lightly over the bearing
surface. Any roughness (which will be
accompanied by obvious bearing wear)
indicates that the crankshaft requires
regrinding (where possible) or renewal. Note
that it is permissible to regrind the crankshaft
to the first undersize without rehardening,
however further regrinding will necessitate
rehardening by Tenifer treatment.
9 If the crankshaft has been reground, check
for burrs around the crankshaft oil holes (the
holes are usually chamfered, so burrs should
not be a problem, unless regrinding has been
carried out carelessly). Remove any burrs with
a fine file or scraper, and thoroughly clean the
oil holes as described previously.
10 Using a micrometer, measure the diameter
of the main and big-end bearing journals, and
compare the results with the Specifications
(see illustration). By measuring the diameter
at a number of points around each journal's

14.10 Measuring a crankshaft big-end

bearing journal diameter

circumference, you will be able to determine
whether or not the journal is out-of-round. Take
the measurement at each end of the journal,
near the webs, to determine if the journal is
tapered. Compare the results obtained with
those given in the Specifications.
11 Check the oil seal contact surfaces at
each end of the crankshaft for wear and
damage. If the seal has worn a deep groove in
the surface of the crankshaft, consult an
engine overhaul specialist; repair may be
possible, but otherwise a new crankshaft will
be required.

1 Even though the main and big-end bearings
are renewed during the engine overhaul, the
old bearings should be retained for close
examination, as they may reveal valuable
information about the condition of the engine.

The bearing shells are graded by thickness,
the grade of each shell being indicated by the
colour code marked on it - they may also have
markings on their backing faces (see
illustration).
Note that the following table only
applies up to the second undersize - for the
third and fourth undersizes, only one shell
thickness is available.

15.1 "STD" marking on the backing of a

big-end bearing shell

B2O2/B234 up to 1993 Thin Thick

Standard Red Blue
First undersize Yellow Green
Second undersize White Brown

B2O4/B234 from 1994 Colour

Thinnest Red
Standard Yellow (only size

stocked as spare part)

First undersize Blue

2 Bearing failure can occur due to lack of

lubrication, the presence of dirt or other

foreign particles, overloading the engine, or
corrosion (see illustration). Regardless of the
cause of bearing failure, the cause must be
corrected (where applicable) before the engine
is reassembled, to prevent it from happening
again.
3 When examining the bearing shells, remove
them from the cylinder block/crankcase, the
main bearing caps, the connecting rods and
the connecting rod big-end bearing caps. Lay
them out on a clean surface in the same
general position as their location in the engine.
This will enable you to match any bearing
problems with the corresponding crankshaft

journal. Do not touch any shell's bearing

surface with your fingers while checking it, or
the delicate surface may be scratched.
4 Dirt and other foreign matter gets into the

15.2 Typical bearing failures

A Scratched by dirt; dirt embedded into

bearing material

B Lack of oil; overlay wiped out

C Improper seating; bright (polished) sections

D Tapered journal; overlay gone from entire

surface

E Radius ride
F Fatigue failure; craters or pockets

Engine removal and general overhaul procedures 2B•21

engine in a variety of ways. It may be left in the
engine during assembly, or it may pass

through filters or the crankcase ventilation
system. It may get into the oil, and from there

into the bearings. Metal chips from machining
operations and normal engine wear are often
present. Abrasives are sometimes left in
engine components after reconditioning,
especially when parts are not thoroughly
cleaned using the proper cleaning methods.
Whatever the source, these foreign objects
often end up embedded in the soft bearing
material, and are easily recognised. Large
particles will not embed in the bearing, and will
score or gouge the bearing and journal. The
best prevention for this cause of bearing

failure is to clean all parts thoroughly, and

keep everything spotlessly-clean during
engine assembly. Frequent and regular engine
oil and filter changes are also recommended.
5 Lack of lubrication (or lubrication breakdown)
has a number of interrelated causes. Excessive
heat (which thins the oil), overloading (which

squeezes the oil from the bearing face) and oil
leakage (from excessive bearing clearances,
worn oil pump or high engine speeds) all
contribute to lubrication breakdown. Blocked
oil passages, which usually are the result of

misaligned oil holes in a bearing shell, will also

oil-starve a bearing, and destroy it. When lack
of lubrication is the cause of bearing failure, the
bearing material is wiped or extruded from the
steel backing of the bearing. Temperatures may
increase to the point where the steel backing
turns blue from overheating.
6 Driving habits can have a definite effect on
bearing life. Full-throttle, low-speed operation
(labouring the engine) puts very high loads on
bearings, tending to squeeze out the oil film.
These loads cause the bearings to flex, which
produces fine cracks in the bearing face
(fatigue failure). Eventually, the bearing
material will loosen in pieces, and tear away
from the steel backing.
7 Short-distance driving leads to corrosion of
bearings, because insufficient engine heat is
produced to drive off the condensed water
and corrosive gases. These products collect in
the engine oil, forming acid and sludge. As the
oil is carried to the engine bearings, the acid
attacks and corrodes the bearing material.

8 Incorrect bearing installation during engine
assembly will lead to bearing failure as well.
Tight-fitting bearings leave insufficient bearing
running clearance, and will result in oil
starvation. Dirt or foreign particles trapped
behind a bearing shell result in high spots on
the bearing, which lead to failure.
9 Do not touch any shell's bearing surface
with your fingers during reassembly; there is a
risk of scratching the delicate surface, or of
depositing particles of dirt on it.

1 Before reassembly begins, ensure that all
new parts have been obtained, and that all
necessary tools are available. Read through
the entire procedure, to familiarise yourself
with the work involved, and to ensure that all
items necessary for reassembly of the engine
are at hand. In addition to all normal tools and
materials, thread-locking compound will be
needed. A suitable tube of sealant will also be
required for the joint faces that are fitted
without gaskets.

2 In order to save time and avoid problems,
engine reassembly can be carried out in the
following order:
a) Crankshaft (Section 18).
b) Piston/connecting rod assemblies

(Section 19).

c) Sump (Chapter 2A).
d) Balance shafts on B204/B234 engines

(Section 9).

e) Flywheel/driveplate (Chapter 2A).
f) Timing chain (and balance shaft chain

where applicable), sprockets and
tensioner, (Chapter 2A).

g) Cylinder head (Chapter 2A).
h) Inlet and exhaust manifolds (Chapter 4A).
i) Engine external components.

3 At this stage, all engine components should
be absolutely clean and dry, with all faults
repaired. The components should be laid out
(or in individual containers) on a completely
clean work surface.

1 Before fitting new piston rings, the ring end
gaps must be checked as follows.
2 Lay out the piston/connecting rod
assemblies and the new piston ring sets, so

that the ring sets will be matched with the
same piston and cylinder during the end gap

measurement and subsequent engine
reassembly.

3 Insert the top ring into the first cylinder, and
push it down the bore using the top of the

piston (see illustration). This will ensure that

the ring remains square with the cylinder walls.

Position the ring near the bottom of the
cylinder bore, at the lower limit of ring travel.
Note that the top and second compression
rings are different.

4 Measure the end gap using feeler blades,
and compare the measurements with the
figures given in the Specifications (see
illustration).
5
If the gap is too small (unlikely if genuine
Saab parts are used), it must be enlarged, or
the ring ends may contact each other during
engine operation, causing serious damage.
Ideally, new piston rings providing the correct
end gap should be fitted. As a last resort, the
end gap can be increased by filing the ring
ends very carefully with a fine file. Mount the
file in a vice with soft jaws, slip the ring over
the file with the ends contacting the file face,
and slowly move the ring to remove material
from the ends. Jake care, as piston rings are
sharp, and are easily broken.
6 With new piston rings, it is unlikely that the
end gap will be too large. If the gaps are too
large, check that you have the correct rings for
your particular engine.
7 Repeat the checking procedure for each
ring in the first cylinder, and then for the rings
in the remaining cylinders. Remember to keep
rings, pistons and cylinders matched up.
8 Once the ring end gaps have been checked

TOP"

17.3 Using the top of a piston to push a

piston ring into the bore

17.4 Measuring a piston ring end gap

17.9 Piston ring cross-section and gap

positioning

Bearing shells should be
renewed as a matter of course
during engine overhaul; to do
otherwise is false economy.

Refer to Section 18 for details of
bearing shell selection.

Рассказать друзьям

Страницы