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Workshop procedures archive

How to strip the power unit for inspection

Relevant to:

  • 9000 B204/234 engines (made after 1994)
  • NG900 B204/234 engines (all)
  • 9-5 B205/235 engines

The power unit featured in the article is from a 9-5 B235 engine that had totally lost all oil pressure on the road but the procedure applies to the 4 cylinder 9000 (after 1993), NG900 and 9-3 (up to 2002). Please note that variants will have slightly different components that are not interchangeable between models.

The following procedure has been developed after carrying out engine dismantling on these cars for over a decade. The observant may note that some photographs may well be from one or more different jobs! Our rationale is to strip the engine into sub assemblies, which, should then be examined separately later.


Tools required

Socket set (air impact wrench & suitable air supply optional)
27mm socket (for timing chain tensioner)
3/8 UNC thread tap
Spanners
Pry bars
Pliers (for dealing with cable ties)
Large circlip pliers (with jaw opening range 120-200mm to remove the oil pump)
Allen keys (for removing the alternator)
Plastiguage strips - SAAB OE part number 30 06 558 (or micrometer)
Whereas you can strip an engine on the floor, a stand makes life simpler


Materials required:

Disposable gloves
Degreaser or other cleaning agent
Oil absorbing granules or sawdust

Estimated time required:
2.25 hrs (including setup and clearing up)


Method

With the engine in the air supported on a crane or hoist, start by draining the sump if this has not been done previously. While the sump is draining, start removing the following:

Direct ignition cartridge (if not removed earlier)
engine wiring loom
intake manifold (and stay bracket)
alternator bracket
power steering pump bracket
water pump
serpentine belt tensioner
breather system
exhaust manifold
turbo-charger

flywheel & clutch or flexiplate (automatic)

Wherever possible, try to replace the nuts, washers, machine screws or bolts that you remove in their respective drillings. Not only will this save considerable time that might be spent wondering which fastener goes where when it all goes back together but also the risk of stripping a thread will be reduced - there are a lot of aluminium alloy parts that can be damaged if the wrong length of fastener is used.

The alternator, rear engine mounting and serpentine belt tensioner need to come off next. Please note the photo of the rear engine mounting bracket - we often see them where a bolt has been left in and the mounting has snapped where it has been forced off!

We usually remove the whole wiring loom at this stage. Although this sounds involved, the reality is that it is a simple procedure with the power unit out of the car and nearly all connectors are colour coded and fit just one location anyway.

At this stage, it is a good idea to time the engine up by rotating the engine clockwise until the the timing marks on the timing case and crankshaft pulley are lined up. Although not absolutely essential if you are going for a full overhaul (assuming no major faults), it makes sense to know how everything should look when the time comes for reassembly.

Remove the Torx screws securing the cambox and lift it away. If it is stuck fast, do NOT prise it apart with a screwdriver but tap it gently with either a rubber mallet or alternatively, place a piece of wood against the cambox and then strike it with a hammer.

After removing the wiring and ancilliaries, tackle the cambox before removing the cylinder head

With the cambox cover removed, there is easy access to the cylinder head bolts. The general state of the engine will likely be pretty good if the camshafts look clean and bright but you will probably find dirty, solidified oil everywhere. In the photograph above, there is a build up of sludge in the cylinder head right next to number 1 bearing cap for the inlet camshaft. As they are easy to overlook, we always start with the two small bolts (arrowed above) that are screwed into the timing case (13mm spanner) and having undone them, we invariably replace them upside down in the timing case (as seen in the photos above). Before undoing the stretch bolts for the cylinder head, the main timing chain needs to be freed from the camshaft sprockets but to do this, the tension needs to be taken off the chain.

With timing chains, we find that if the engine is having an overhaul, nothing less than full replacement of all components will do. This is because although the parts removed may look OK to reuse, the degree of wear only becomes apparent when compared side by side with new parts. SAAB offer a kit that includes both main and balance shaft chains, plus all gears/sprockets, rails, guides and even the correct anaerobic flange sealer (actually Loctite 518) for substantially less than the cost of the parts if purchased separately. Undo the tensioner and set aside (this is the ONLY part NOT included in the SAAB kit!)

With the tension backed off and the chains slack, undo the bolts fastening the camshaft sprockets. These may need tapping gently with a mallet. Lift the chain away but replace the sprocket bolts in the camshafts. With the help of assistant -the chain needs pulling up so that the slippers don't stop the head as it is lifted- lift the cylinder head away from the block.

IMPORTANT: never place the cylinder head face down on the ground because there is a danger that valves can be bent. Always use small blocks of wood (or cylinder head stands) to prevent this from happening. Place the cylinder head on blocks above newspaper/cardboard (it may leak a fair bit of oil!).

Discard the cylinder head stretch bolts - they should always be replaced on these engines, as they have a bad habit of working loose at the best of times BUT recover the x2 locating dowels from the cylinder block - trust me: locating the head without damaging the new gasket without these is difficult. Put them somewhere safe NOW!

Removing the the timing case is an operation that is best undertaken with an impact driver or impact wrench, as the heads of the torx type bolts can slip, making removal very difficult. The casing will be tight even with all the bolts removed, as it is located precisely with two dowels (location D in the photo below) and it is usually necessary to tap it free with a suitable block of wood and a mallet.

Timing case dowels MUST be removed

The dowels are critical for correct alignment of mating faces containing oil galleries but MUST be removed. If the dowels are not removed, it will be impossible to refit the cover on without damaging the head gasket. No amount of sealant will stop the engine leaking like the Exxon Valdez if this happens - so don't take the risk! It is easy to underestimate the importance of this step and extracting the dowels may seem like a lot of trouble to go to but it is nothing less than an essential step.

The author urges readers to resist the temptation to try to remove the dowels with self-grip wrenches or pliers under any circumstances because the dowels will be damaged.

The easiest way to remove the dowels is to cut a 3/8 UNC thread inside the dowel. Use a firm hand and plenty of oil, then screw a bolt inside the new thread before using a slide hammer to shock the dowel free. Very often, the dowel will start to spin and can be unwound with the cutter, without the need for a slide hammer. Put the cover to one side for examination later and make sure that the dowels are placed somewhere safe because you will need them later. Be reassured by the knowledge that refitting the dowels is very simply achieved.

Timing gears MUST be stripped ina set order to avoid problemsRemoving the timing chains, gears and rails must be approached in the correct order. Start by undoing the chain gear above the exhaust balance shaft. This bolt does NOT come in the kit and the head is very easily stripped so use an impact wrench. This bolt has to be undone first because otherwise the chain will not stop the gear from spinning, which will make it very hard to remove.

Remove all rails and guides, replacing the bolts as you go. The balance chain tensioner is secured by x2 bolts and should be discarded as it is included in the SAAB repair kit. With the balance chain off, its flimsy nature can be appreciated - side to side wear and worn guides allow the chain to chatter. In extreme cases, the chains can snap and cause serious damage.

The benefit of an engine stand only really becomes apparent when the time comes to tackle the sump because most offer a swivel function that allows the engine block to be inverted. Remove the sump. and set aside as a sub assembly for inspection later. Next, undo the connecting rod bearing caps.

You will need to turn the engine (temporarily refit the crank pulley) to gain access to all the caps. Lift the cap off and carefully lower the connecting rod past the crankshaft journal and remove from the cylinder. Bearing caps are number stamped but refit the cap and store somewhere safe. Please note that connecting rod design has changed during production. Early engines tend to use bearing caps that are flat and secured with multi-sided nuts whereas later units use serrated type caps secured by bolts with hexagonal heads.

Examining the cylinder bore/cylinder block
The author has yet to see a cracked cylinder block but it pays to check for frost damage in the form of cracks around the frost (core) plugs or cracks between cylinders at the top of the block. In the case of cylinder liners, these need checking for cracks if the engine has been suffering mysterious coolant loss. Non destructive testing techniques involve use of a penetrant dye oversprayed with a developer, Zyglo, for instance.

Checking the block involves looking for cracks, spun shells and scored cylinders

Cylinder bores are likely to show most wear at the top - the bottom of the bore seldom wears. A slight wear ridge at the top is inevitable but what we are looking for is further down where there could be damage on the thrust sides from seizing pistons caused by no lubrication at the piston cooling jets -always referred to as 'Benny and the Jets', (after the Elton John song)by one seasoned SAAB technician we know- in the bottom of the cylinder block. The cylinder block can be honed to remove slight wear and this must be done if new piston rings are to be fitted.

Examining the pistons

Piston seizure is a major cause of crankshaft bearing failure due to lubrication issues
When all pistons are removed, they should be examined. What you do not want to find is heavy scoring on opposite sides of the skirts because this results from lubrication failure.

The photograph (left) shows a typical piston failure scenario but note that cast pistons can fail without warning on highly tuned applications. Forged pistons are strongly recommended.

Only a few minutes running in this state trashes the cylinder because the piston rings become compressed in their lands and the massive increase in friction causes the crank to suffer bearing failures.

In the event of a knocking crankshaft, 9 times out of 10, a rebore will be required. A rebore is a precision job and not too expensive but oversize pistons are a king's ransom and a set carries a £400 premium over the standard items. In such a situation, we would use forged rather than cast pistons - a set of Wossener forged pistons (available in 0.5 or 1.0mm oversizes) costs around £500 inc VAT and delivery.

Examining the connecting rods
Check the connecting rod bearing shells. Ideally, these should be dull gray but what you will most likely find is that the shells are scored, worn to the copper or worse still have spun in the bearing cap. Main bearings suffer similar damage and spun shells here usually means a new engine. Flat type bearing caps can be re-machined by line boring (serrated types cannot be restored) but this is a skilled job for a precision engineering shop and hardly cheap.

If you plan on building an engine with more than the standard output of the Aero (i.e more than 250bhp) forged pistons are a must and consideration should be given to having the connecting rods checked for cracks and then shot peened and balanced. For serious power, though, consider uprated connecting rods, along with other goodies like one piece flywheels, big valve cylinder heads and uprated camshafts which are available to special order from Abbott Racing.

Examining the crankshaft
As above, the shells should be a uniformly matt gray colour and running a finger nail over the crank journals should not reveal the presence of any ridges. Crankshafts can suffer from neglected oil changes but occasionally, over enthusiastic driving (like dumping the clutch at high engine revs, for example) has been known to bend crankshafts. Checking the throw of a crank or correcting the stroke are specialist services that only a handful of readers are likely to require.

Most owners will not have access to a micrometer but a journal that looks OK can be checked by using a Plastiguage. These are strips that are tightened down under the bearing cap that enable the amount of wear (ovality & taper) to be checked by the extent to which the strip is flattened. This works by measuring the strip at its widest point -the graduated scale is printed on the back- after the cap has been tightened down, then removed again. Of course, your friendly local engineering shop will be happy to measure crankshaft journals for you. If the journal wear is within tolerance, it is possible to polish the crank. Expect to pay around £50 for this highly specialised work and know that it is worth every penny. Smiles Engineering (Newcastle) have polished several crankshafts for us with excellent results.

No need to use a micrometer to measure the crankshaft jounals here: the shells show excessive wear and signs of oil starvation

Readers need to know that there is an oil feed from the centre main bearing cap to the balancer shaft and this must be checked by blowing compressed air down the drilling, as what can happen is that the balancer shaft bearing can rotate, shutting off oil supply. This scenario requires a line bore at a specialist machine shop and (ideally) the SAAB special tool 83 94 470 to remove/install the new bearings (x1 bearing per shaft).

Examining the timing case

Check timing case for cracks and ensure the oil pressure relief valve thread has not stripped

The timing case can suffer wear from an excessively worn timing chain - so check for deep grooves on the inside and cracks on the outside but the main reason these end up in the scrap bin is a failed thread on the oil pressure relief valve drilling. The valve and spring lurk beneath the cap (circled red in the photograph on the left)

This is tricky to reclaim by helicoiling and if damage is found, the easiest option is to acquire a good used cover.

It certainly pays to remove, clean and inspect the valve for wear. The timing case also contains the oil pump, which lives beneath the large circlip.

Unlike many other engines, the pump can be refurbished very cost effectively by simply replacing the drive gears and oil seal but this can be done only if the reverse side of the metal cover that locates the crank pulley seal is unscored.

 

Examining the cylinder head
Full examination of the cylinder head involves removal of both camshafts, hydraulic lifters (tappets), valves, caps, springs and collets but a quick check is all that is required at this stage. The rationale behind not stripping the head right down to its component parts is this: dismantling is time-consuming but relatively few heads will be beyond reconditioning and stripping the head is an activity we generally carry out while other parts are being machined at the engineering shop.

With the cylinder head supported on wood blocks or on proprietary head stands, look at the general condition of the camshaft lobes. Grooving or scoring is bad news and points to oil starvation but this happens only in extreme cases.

Check the exhaust manifold studs - as a rule, we always replace these as a set whenever a cylinder head is removed because we have found that many cars run for thousands of miles with snapped studs (check for tell-tale carbon marks or a burned gasket) but a stage is reached when others will become stressed and or wasted. It is much easier to tackle these with the head off the block and a kit exists (about £10) that is well worth the investment. Expect to find at least one snapped stud!

With the head upside down, scrutinise the mating face (the cylinder head gasket sometimes sticks to the head itself) for any sign of pitting or cracks. Check that the mating face is level by running a straight edge (steel rule or similar) over the entire surface. Any distortion -try running feeler gauges under the rule- means the head will need to be surface ground (skimmed) but this is rare with these engines.

Check cylinder head for cracks between valves and combustion chambers. Also check for flatness with a steel rule or other suitable straight edge

Cracks if present would tend to occur in one of two places: between the valve seats or inside the ports but again this is very rare and if found we would just get another cylinder head from the stores and simply swap camshafts (2.0 and 2.3 heads are the same but note that the 9000 and 9-5 have different cylinder heads and therefore different gaskets).

Erring on the side of safety -we will cover a full cylinder head overhaul in workshop procedures later this year- but please note the following traps for the unwary if you cannot wait for this article:

  • Camshafts are generally NOT marked (ergo easy to mix up) so mark accordingly so this cannot happen
  • Camshafts between 2.0, 2.3 and Aero variants may be different
  • Camshaft bearing caps are secured by bolts - note that the inboard ones are GROOVED - this is the oil supply. Do NOT mix them up!
  • Valve spring compressors need selecting with care (and collets are fiddly to remove!)
  • Valve lifters (tappets) must be marked and NOT mixed up
  • Care needs to be taken if valves need swapping because clearances may be outside permitted limits
  • Valve stem oil seals are not cheap but should always be changed!
  • Cylinder head stretch bolts MUST be renewed

Finally, overhauling a cylinder head on a 9-5 B205/235 is not a 5 minute job. Just cleaning the thing properly will take much longer than you expect. Grinding the valves and decarbonisation takes time too but is certainly worthwhile.

 


Coming next...
A major series of new features walking readers through the various stages of reconditioning a SAAB 9-5 engine:

  • cleaning engine parts effectively and safely
  • rebuilding the cylinder head
  • rebuilding the timing gear
  • changing balancer shaft bearings
  • overhauling the cylinder block: reboring the block and fitting oversize pistons
  • overhauling the crankshaft: regrinding or polishing the crankshaft and fitting new shells
  • overhauling the timing case: replacing the oil pump gears and oil pressure relief valve

The series will not necessarily be uploaded in the order above and the author hopes readers will understand that even the article above took far longer to write, check and find suitable photographs to support than completing the actual job itself.

ANY of these procedures constitutes a major repair and even if you have no intention of doing any of these jobs, the articles will help you understand the workings of your engine and the true cost of skimping on maintenance.

The author hopes that readers will be pleased to learn that even badly damaged engines can yield at least some reusable parts and not all the components featured in the engine above were consigned to the scrap bin.

Return to the workshop procedures page

Page updated February 28th 2010

 


 

 

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