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Workshop procedures archive

Assembling the crankshaft & pistons on the SAAB B205 & 235 engine
Applies to SAAB 9000 (from 1993), NG900 , 9-3 (9400) up to 2002 & 9-5 (9600)

1.0 Introduction

This operation is part of a full engine overhaul and cannot be carried with the power unit in the car or with the gearbox still attached to the engine. Removing the power unit without dropping the subframe and dismantling and inspecting the engine are procedures that have been covered within the workshop procedures archive. The archive also details fitting timing chains, cleaning and remeshing the sump strainer and changing the balancer shaft bearings.

Readers should be advised that removing a power unit, separating the engine from the transmission, stripping and inspecting the components is a major undertaking. Considerable time must be spent cleaning components and keeping the workshop environment tidy. Dirt and grit are the enemy but the working area can quickly become a mess - time spent looking for tools in the resulting chaos wastes time. If a crankshaft requires a regrind or polish and the cylinder block requires a rebore or hone, do bear in mind that these are precision operations that cannot be completed in 5 minutes. A good machine shop will be very busy and it could take up to a week for the job to be completed but this will present the ideal opportunity to clean and prepare all other components like the timing case and assemble components required. Do bear in mind that a SAAB dealer's Parts Department is extremely unlikely to carry many of the parts you require and they will need to be ordered.

1.2 Tools required:

Socket set, torque wrench, angular torque wrench adaptor, piston ring compressor
An engine stand is strongly recommended - investigate the possibility of hiring one if you don't want to buy one.

1.3 Also required:

Latex gloves, pipe cleaners, cotton buds, waste rags, hand cleaner, cleaning solvent, brush & shovel, refuse bag

The SeriousSAAB basic engine rebuild kit:

The SeriousSAAB engine rebuild kit - showing just some of the parts required

2.0 Method

Start by removing the plug from the oil gallery that feeds the piston cooling jets.  Blow compressed air through the gallery, using aerosol carburetor or brake cleaner with a long flexi spout if in any doubt that the gallery is not perfectly clean.

An engine stand helps keep the work area tidy. Start by removing the oil gallery plug and blow through with solvent and air.

Soak the cooling jets in paint thinner for at least 30 minutes.  Use paper to clean away any oil residue or dirt, then use compressed air to ensure they are not blocked.  Replace the jets and nip up with a suitable socket (14mm) and ratchet wrench.  Torque down the jet bolts to 18 Nm.

Blow through each oilway in the cylinder block, then wipe clean each main bearing housing.  Fit new main bearing shells to each housing, noting that they fit only one way.  Our crankshaft had been checked and reground 0.25mm undersize by Smiles Engineering (Newcastle Upon Tyne), who also rebored and honed the cylinder block 1mm oversize.

Sourcing shell bearings is tricky: we have found that it is cheapest to buy standard size shells from SAAB dealers but undersize ones from SAAB are ruinously expensive, so use Federal Mogul shells instead.  For some reason, these are not listed in many catalogues and you may need to find a supplier who deals with Scantech or Speedparts (Sweden) to acquire them.  See Parts Used & Suppliers section of this article.

Lubricate the shell bearings.  Check ALL oilways in the crankshaft are free from dirt or contaminants by pushing pipe cleaners through them. When you are satisfied the crankshaft is as clean as possible, lower it into position with great care.  Use petroleum jelly to assemble the thrust washers to either side of the centre main bearing (number 3).  Note that the thrusts are fitted with the grooves facing outwards.

Fit the main bearing shells and thrust washers then lower the crank into position

Fit a new shell bearing to the centre main bearing cap.  The caps are numbered to avoid confusion and the design incorporates dowels and recesses to ensure correct alignment.  Use a ratchet wrench and suitable socket to nip bearing cap down.  Check that the crank can still move freely before using a torque wrench to achieve a final tightness of 22 Nm. Then use an angular torque wrench to tighten the bolts a further 70°.

Main bearing caps are numbered and fitted with dowels to ensure correct alignment

Follow a similar routine with the other bearing caps, checking that the crank does not lock up when the bolts are tightened fully.

2.1 Fitting the pistons and connecting rods

Since we had our cylinder block rebored, we needed to fit the new oversize pistons to the connecting rods. The connecting rods had, of course, been checked earlier because B205 & B235 engines often suffer damage to cylinder bores due to lubrication failure that results in piston rings becoming compressed in their lands so that the actual piston skirt drags down the thrust side of the bore. If the engine isn't stopped immediately, the big end bearing shell tends to spin, trashing both the connecting rod and the crankshaft journal. It is ESSENTIAL to understand that many 9-5 engine rebuilds go wrong because technicians see only the damaged crankshaft journal (effect) and fail to realise that this occurs because the pistons were seizing in the bores. (cause)

Connecting rods MUST be in A1 order! This means that they must be cleaned thoroughly and the bearing surfaces polished up, if they look grubby. The author uses a very small amount of Brasso and the surfaces are then cleaned again. Connecting rod types MUST NOT be mixed within one engine and pistons from different makers must NOT be mixed.  This is because the reciprocating mass will not be balanced.  Connecting rods should only be changed as a set. The golden rule therefore is to use only pistons and connecting rods of the same type and make.

Pistons are secured to connecting rods by snap rings that stop the gudgeon pins from falling out. Use a small screwdriver placed in the recess in the piston (see photo) to prise out the old gudgeon pin snap rings and then push out or drift out the gudgeon pin. Be advised that there are a number of rules that need to be observed when fitting connecting rods, snap rings and pistons:

  • Compression ring gaps MUST be at 180° to each other
  • Oil control ring gaps MUST NOT be in line with any other gaps
  • Gudgeon pin snap rings MUST be fitted with the open end facing UP (essential)
  • Arrows on the piston crowns MUST face timing chain end of engine
  • Numbers stamped on the connecting rods MUST face the exhaust side of the engine

Observe fitting rules in text! Snap rings MUST have the gap at the top, arrows on piston crown face timing chain end and con rod numbers MUST face the exhaust side of the engine

Lightly oil the cylinder bore. Lightly oil the piston rings. Assemble the piston ring compressor and lower the connecting rod and piston into position, making sure that the rod does not touch the crankshaft journal. Gently tap the piston crown down the bore using the wooden end of a hammer and protect the piston crown with rag. Rotate the cylinder block on the engine stand and then fit the two bearing halves. Note that connecting rod numbers face the same direction. Nip the nut/bolt down then torque down with a torque wrench. Connecting rods may be one of two types and this has implications for the torque settings:

  • Serrated cap (with bolts) 25 Nm +100°
  • Flat cap (with nuts) 20 Nm +70°

As each connecting rod is assembled and torqued down, the author likes to rotate the crankshaft. If this is done, any fault found must relate to the last bearing fitted. Try to avoid distractions when carrying out this job - the author will admit to having replaced at least one bearing cap the wrong way round in the past!

Pistons and bores should be oiled lightly before the compressor is fitted and the piston fitted into its bore. The crown must be protected when the pisto is tapped down the bore with a hammer shaft.

2.2 The next steps: refitting the oil filter housing & oil transfer pipe

If the oil filter and thermostat housing has been removed for cleaning, blow it through with compressed air and apply a thin bead of Loctite 518 anaerobic flange sealant to one of the mating faces and tighten down the fasteners. Next, ensure the oil transfer pipe is clean then fit new 'o' rings to each end and fit in position (see photograph). The pipe is a simple push fit and cannot fall out when the sump is in situ. When the pipe and housing are fitted, the engine should be inverted and the cylinder head and gasket installed.

Always change the seals on the oil transfer pipe (inc. in timing kit). Clean oil filter housing and refit then install the pipe (a push fit). The cylinder head and gasket are refitted next, then the timing gear and cover before the sump.

Fitting the cylinder head and gasket will be covered in a further article covering a full cylinder head overhaul including regrinding valves and renewing the valve stem oil seals while an additional feature will cover fitting the ancillaries, mountings, flywheel and turbo charger.

2.3 Connecting rods & pistons: additional information

As explained earlier in the article, connecting rods can suffer from damage due to spun bearings. Connecting rods with flat type caps can be reclaimed by machining and line boring but these are precision engineering operations for skilled staff. Serrated type connecting rods may not be reclaimed because the mating faces are irregular. When one or even two connecting rods are needed, the whole set should be changed. Good used sets do exist but these need checking for alignment and cracks by a good engineering shop at the very least, while having the weights checked is also sensible because the maximum permissible variation is less than 6 gram.

Those wishing to do the job properly should have the connecting rods end-over-end balanced, the pistons balanced, the flywheel lightened (or replaced with a single billet steel flywheel) and the engine balanced as a rotating assembly with clutch. Crankshafts too can be stroke corrected and crack tested.

The author strongly recommends the replacement of standard B205 & 235 pistons with Wössner Forged T6 alloy pistons, irrespective of whether the pistons are worn or not! Having the block bored oversize results in a useful increase in capacity and we believe that since a block is only going to be rebored once, it is shrewd to bore +1mm (to 91mm) rather than +0.5mm. Wössner pistons are the ideal solution for those seeking to build a B205 or 235 engine with a power output greater than 300 bhp.

It is known that the standard pistons are not as strong as those used in the SAAB 9000 and tuned applications have been seen where the entire side of a piston has broken away for no apparent reason. Investigation by the SeriousSAAB team leads us to believe that such failures may be related to ill advised tuning that disables the engine knock sensor which allows detonation OR through a defective direct ignition module. In any event, tuned engines or those with nitrous oxide injection simply MUST be fitted with forged pistons. It is ironic that here in the UK a set of the superbly made Wössner forged pistons actually costs rather less than standard (but oversize) pistons from SAAB.

Elsewhere, readers may have encountered those who advocate the use of a B204 or 234 engine in a 9-5. The author's opinion is that such a move is retrograde because it involves compromises and since the main and crucial difference between the two designs relates to the pistons, it makes far more sense to upgrade the B205 & 235 pistons to forged specification. Special connecting rods are available from tuners like Abbott Racing for those who are looking to build road burning 9-5s with engine outputs greater than 400bhp.

Connecting rod and piston information
Engine Con rod centre to centre Compression ratio Wössner +0.5mm Wössner +1mm
B205 159 mm
8.8 : 1
K9120D050
K9120D100
B235 153 mm
9.3 : 1
K9119D050
K9119D100

 

3.0 Parts & components used

Wössner forged T6/molybdenum pistons 1mm oversize.
Federal Mogul main bearings 0.25mm undersize (ScanTech 53.0941)
Federal Mogul connecting rod bearings 0.25mm undersize (ScanTech 53.7651)
Federal Mogul thrust washers (ScanTech 53.7271)
SAAB balancer shaft bearings
SAAB balancer shaft blanking plugs
SAAB Oil pump kit
SAAB Timing chain renovation kit
SAAB Breather fix kit
SAAB thermostat
SAAB oil pressure sensor
SAAB oil pressure relief valve
SAAB oil pressure relief valve spring
SAAB Cylinder head gasket
SAAB Valve stem oil seals
Cylinder head bolts
Exhaust manifold stud kit

 


Suppliers

The author would like to take this opportunity to thank the organisations listed below for delivering consistently a level of service well above the norm.

Abbott Racing
Well known SAAB tuners of many years' standing with plenty of advice for the NG900, 9000 & 9-5 owner. Abbott Racing supplied our Wössner pistons.
http://www.abbottracing.net/


Euro SAAB Parts Direct
The author is any Parts Manager's worst nightmare because components required will be anything except the expected. ESPD have supplied all the original, genuine SAAB components for the rebuild above except the pistons and undersize shell bearings and at very sensible prices too. Our first stop for genuine SAAB parts.
http://www.euro-saab-parts-direct.com


Smiles Engineering Ltd (Newcastle upon Tyne) http://www.smilesengineering.co.uk/
A busy precision engineering machine shop with hugely experienced staff who take great pride in their work. A number of very badly damaged and frankly abused SAAB engines have been brought back from the dead. Smiles Engineering reground the crankshaft and rebored and honed the cylinder block in the article above. Exemplary work is the norm here but whereas readers can see that the crankshaft and cylinder block look good, no amount of photographs can convey how good the engine feels when spun over by hand.

Return to the Workshop Procedures Archive page

 

Rebuilding the SAAB 9-5 engine block, how to rebuild the SAAB crankshaft, SAAB 9-5 piston failures and how to fix them, SAAB 9-5 B235 full engine rebuild by the UK's leading SAAB enthusiast.


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