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Workshop procedures archive

Overhauling the cylinder head on the SAAB B205 & 235 engine
SAAB 9000 (from 1993) & NG900 operations are similar, 9-3 (9400) up to 2002 & 9-5 (9600)

Tools:
Socket set, terminal screwdriver, magnetic retrieval tool, marker paint pen (or scribe), drift, hammer, valve spring compressor, valve lapping stick, electric drill, torque wrench, angular torque gauge, stud extractor, engineer's square. Cylinder head stands are recommended, as is SAAB valve stem oil seal tongs.

SAAB valve sea tongs aren't necessary to complete this job but a good quality valve spring compresser is mandatory.

Materials:
Valve grinding paste, waste cloth, paper roll, degreaser, wet and dry paper. Disposable rubber gloves are recommended, as is hand cleaner. An old plastic bottle can prove useful too (see text below!)

Components:
Cylinder head gasket, valve cover gasket set, cylinder head bolts (x), manifold stud repair kit, thermostat, timing chain tensioner oil seal (composite), timing chain tensioner plug seal ('o' ring)

Introduction & background
In normal operation, there should be little need to lift the cylinder head, however, oil leaks from the cylinder head gasket at both corners are not unknown and sometimes, the cylinder head bolts can work loose. As a rule, a failed cylinder head gasket on either a B2x4 or 2x5 engine will present with the following symptoms:

  • Overheating and coolant loss
  • Coolant contaminated with oil, especially in the coolant reservoir
  • Pressurisation of the cooling system (watch for ballooning coolant hoses)

Make no mistake, removing a cylinder head and changing the gasket is not a trivial operation and garages in the UK will charge between £300-500 for this work, depending upon the scope of the repair and the geographical location of the workshop. For this reason, it is essential to diagnose a cylinder head gasket failure correctly (unless the engine is to be stripped as part of a general overhaul anyway). For a definitive diagnosis, find a garage with a leak detector. Garages generally use a tester filled with a detector fluid that screws onto the coolant reservoir - when the engine is running, the colour of the detector liquid will only change if it comes into contact with exhaust gases. Since exhaust gases should not be present in the coolant circuit, their detection is irrefutable evidence of a major problem that warrants removal of the cylinder head. In more than a decade, the author has yet to see a B2x4 or 2x5 engine with a cracked cylinder head. The cylinder blocks do not crack liners because there are no liners - the cylinder is bored directly into the cylinder block.

Don't change a head gasket if an oil leak is the problem without checking the timing chain tensioner seal! Frequently mis-diagnosed by those who should know better.

Readers should take note that oil leaks around the top of the timing case, particularly at the back of the engine are often caused by a leaky composite washer on the timing chain tensioner - for this reason, always renew this washer when removing a cylinder head for any reason. Another relatively inexpensive component that should be binned routinely is the thermostat. The author is particularly irritated by lack of aptitude on the part of some workshops, who do not seem to have grasped the basic concept of cause and effect: cylinder head gaskets do not fail without reason and changing the gasket alone only treats the effect - if the underlying cause is a blocked radiator, or a defective thermostat, the problem will recur. Owners too, sometimes do not escape the author's wrath: if your engine overheats, STOP immediately and let it cool down. Of course, overheats will happen at inconvenient times but major damage can result through pressing on and repairing that will not only be inconvenient but most likely expensive too.

Pre-requisites

The procedure below assumes that the cylinder head has been removed from the engine (see the article on stripping the engine)

MethodDo not lay the head flat when the camshafts are fitted - it may bend the valves. Also note that the tappet sliding surfaces must be protected when compressing valves or renewing seals.

Tip as much of the oil in the camshaft galleries as possible into the waste oil container, then mount the head on stands. The author prefers the simple and effective design of Sealey head stands (Part VS 1555). These are a pair of 'L' shaped stands with tapered prongs that locate by sliding into the cylinder head stud holes. Clean a suitable area on each camshaft and then mark 'in' on the inlet camshaft and 'ex' on the exhaust cam to avoid any possibility of mixing the cams up.

Never lay the head flat while the camshafts are still fitted. Mark cams and braing caps if the numbers cannot be read easily - these parts must NOT be mixed up.

Before undoing the camshaft bearing caps (keeps) note not only that each is numbered but also the numbering sequence. If the numbers cannot be seen easily, mark them up, following the original scheme. Undo the camshaft bearing cap bolts, progressively, then lift out the camshaft. Store the camshafts somewhere dry where they cannot roll. Before lifting out each tappet, clean the top and apply a number with marker paint because it is important that each one is returned to its original position. The author finds that modular plant trays are very useful for storing the tappets

Ensure that the camshaft bearing caps (keeps) are numbered in a way you can read, then number the hydraulic lifters too. A modular plant cell tray is handy for storage but glue it to a sheet of plywood for extra strength.

In the absence of SAAB special tool 83 93 746 (protective collar), make a substitute by taking an old plastic bottle and cut out a section from the middle and trim until it may be installed inside the tappet chamber to protect the sides.

Before attempting to compress the valve springs to access the retaining collets, take a suitable drift - we use an old piston gudgeon pin!- strike the tops of the valves. This makes the compressing operation easier - if this is not done, the spring may be so hard to compress that the valve spring compressor tool will be damaged.

Compress the spring and recover the collets. Note that a small screwdriver and magnetic retrieval tool makes this operation very much easier, as these valves and collets are far smaller than would be found on older engine designs, like the B series unit found in the MGB, for instance. Lift out the valve springs and caps and store safely, the recover the valve and store it carefully. It is essential that valves are returned to their original location - they must not be mixed up. SAAB dealerships have a special valve rack, which is part of the T3 engine toolboard but owners can improvise with cardboard to make something equally effective.

Cut up an old pop bottle to make a protector for the tappet (lifter) bore. Strike the top of the valve with a mallet and suitable socket to free it to avoid damaging the valve compressor. Then, compress the valve and retrieve the collets.

Before recovering the plastic shield, (ideally) use SAAB tool 83 94 157 (valve guide oil seal tongs). This is part of the author's kit because the tool makes removing the seals simple - any other tool may not fit the deep recess so effectively. The seals MUST be replaced as part of an overhaul.

Be sure not to mix up valves and their components! Keep the collets safe. Check valves for trueness in a drill but use an engineers square to see  the springs are straight.

Inspecting the valves and seats
Generally, performance is sapped over time by the effects of combustion. As the mileage builds up, the valve seats -particularly on the exhaust side- will lose their seal and become pitted whilst carbon deposits will build up in the exhaust ports and around the heads of the valves. Inlet valves simply do not require decoking and the seats are seldom damaged by pitting. Exhaust valves are usually quite pitted but pitting can extend to the seat in high mileage cars. Try grinding but also consider employing the services of a machine shop to recut the valve seats and reface the valves if they look really poor.

The easy way to check each valve for trueness by mounting in an electric drill and spinning at speed - any distortion will be apparent instantly. Clean each valve, then remove the carbon build up in the chamber and around the exhaust port. Note that this may take some time! The author usually vacuums up the resulting mess before blowing out each chamber and valve guide in turn using compressed air.

Lapping the valves
Valves should be lapped by hand in the traditional way using a stick attached to the valve by the suction cup rolled between the palms of the hands, with 3 small dabs of coarse carborundum paste on the valve. The objective is to obtain a thin, consistent seal on both valve and seat with no pits evident on either surface.

Lapping or grinding valves is straightforward but can take time

After lapping, the valves should be cleaned of carbon deposits and the valve mating surface and especially the valve stem should be cleaned with petroleum, thinners or similar solvent.

Refitting the valves
When the valves and seats have good seats and have been cleaned, the exhaust port within the cylinder head should be cleaned with solvent. The valve guide should be oiled (lightly) before fitting the new valve stem oil seals. Note that these should also be oiled before fitting with the SAAB tongs - use the protector made from the plastic bottle made earlier to protect the lifter (tappet) bore.

All the valves, valve guides, springs and cap washers need cleaning properly and oiling. Replace the valve stem oil seals and apply oil to them too.

Push the inner spring inside the outer valve spring, then fit the spring washer before compressing the assembly with the valve spring compressor. Refitting the collets is fiddly and the best advice is - don't rush! The author prefers to position the collets using a terminal screwdriver with a dab of petroleum jelly.

Refitting the collets when the val;ves are compressed is fiddly. The author uses petroleum jelly on the end of a terminal screwdriver to wangle the collets into position.

When satisfied that the position is correct, gently release the spring compressor tool. The collets should be pulled into the correct position. Check each valve spring assembly has been built up correctly by striking the valve washer lightly with a hammer and socket (wear eye protection to guard against the risk of collets being ejected).

Refitting the camshafts
Before the camshafts can be fitted, the hydraulic tappets (lifters) must be cleaned. This is best done on a one at a time basis and the lifter should be squeezed gently between the jaws of a vice -the lifter must be protected by thin pieces of wood- to squeeze the dirty old oil from the lifter. Wash the lifter in a suitable solvent, remove the number you painted on at the outset and oil lightly before refitting in the tappet bore. When all lifters are refitted, the camshaft bearing caps should be cleaned one at a time before refitting the camshaft. As before, note that the mating face of the cylinder head must not be laid flat to avoid damage to the valves. Use a cylinder head stand or simply place blocks of wood beneath each end of the cylinder head to raise it.

VERY IMPORTANT! Please note that the camshaft bearing caps (sometimes called keeps) only fit ONE way and that the inner bolts are the camshaft's oil supply and have a slot machined into them. Tighten the cap bolts slowly and evenly.

Be sure not to mix the bots up for the camshaft bearing caps - the ones on the inner side of the cylinder head have oilways machined into them!


Refitting the cylinder head

Ensure that the two locating dowels are in position; during a rebuild, small components like the dowels can become mislaid but the dowels are essential for correct alignment. Do not attempt to fit the head without the dowels - if they are missing, they should be replaced. Note that the cylinder head gasket will fit only one way when the dowels are fitted (the gasket will probably be marked 'Top' anyway). It is wise to use a spot of Loctite 518 sealant at the very corners of the timing case/cylinder head joint. The help of an assistant is essential - an extra pair of hands is required to guide the timing chain through the aperture in the cylinder head without snagging on the chain guide. Use elastic bands to tie the guides together. Note that this step must not be rushed - the chain guide is easily damaged and brittle: if it breaks, it really does make a LOT of work.

Loosely replace the two bolts on the lower face of the cylinder head that locate in the timing case, then locate the new cylinder head bolts and nip up so they are hand tight before following the tightening sequence below.

Use this table to achieve the correct torques for the head bolts plus the two bolts in the timing case.

Please refer to the instructions included in the article on changing the timing chains for details how to refit the camshaft sprockets, timing the engine up properly and refitting the timing chain tensioner correctly: http://www.serioussaab.co.uk/Procs_pages/proc_pages/p_chain.html

Refitting the cambox cover comes next but make sure that it is cleaned thoroughly. In particular, ensure that the two metal pipes that face downwards are blown through with compressed air, as a blockage here can cause blue smoke upon startup.

Clean the cambox properly and blow through the downward facing metal pipes, which, if blocked, can lead to blue smoke in the exhaust when the engine is started.

Use Loctite 518 flange sealant on the large semi-circular pieces of the rubber gaskets so they locate properly. Experience has proved that only genuine SAAB gaskets fit properly, so use anything less at your peril. Do take your time fitting the cambox, as it is alas all too easy to end up with the gasket slipping and trapped, whereupon it leaks. In particular, do take the trouble to ease the securing torx bolts through the gasket slowly and carefully. Torque down to 15Nm or 11lbs/ft using the sequence provided below:

Cambox bolt tightening sequence

Now, check that the breather pipe connections have been fitted and if a complete new breather system is not being fitted do ensure that the main pipe from the cambox to the separator is not showing a disturbing similarity to the consistency of licourice, as when this pipe fails on the road no good ever results as the outcome.

Before building up all the ancilliaries, do please change the thermostat. It is a nice easy job ( just make sure that the hole in the thromostat points upwards) which should be done to protect the work that has been done. The author buys only SAAB thermostats.

 


Cylinder head know-how: part numbers, interchangeability and applications

The cylinder head design for B2x4 and B2x5 engines is different, as is the cylinder head gasket. In days of yore, Classic 900 owners often used to buy the author's spare 2.3 cylinder heads to upgrade their 2.0 litre engines but on the B2x5 engine, the bare cylinder head on 2.0 and 2.3 litre engines is the same part (OE part # 55561380). Readers should note that the Aero has different exhaust valves (the size appears to be the same but the material is different) and that camshafts vary between models and years.

Cylinder head height (nominal: ex works condition): 139.4-139.6mm
Cylinder head height (after surface grinding): 139.0mm

Be very careful when changing original SAAB valves for valves sourced elsewhere! The height of the valve becomes critical because if it is outside specification, the engine could have no compression or no valve clearance when the lifters fill with oil. For this reason, there is a special SAAB service tool to check the valve height. In normal service, grinding in valves will not cause a problem but avoid grinding more than is strictly necessary.

Big valve cylinder heads are the route for tuners who want to go further than upgraded electronic control units, free flow air filters and less restrictive exhaust systems. The logic here is simple: altering the valve duration and size by fitting different camshafts will pay dividends by allowing more fuel to be burned. Any tuning shop should be able to polish and port a head for minor but worthwhile gains but developing camshaft profiles that alter the characteristics of the engine at higher speeds without destroying low speed driveability is the realm of experts. As a rule, there is little point in fitting a big valve cylinder head with 'warmer' camshafts without a bigger intercooler and altering the exhaust and fuelling arrangements. Tuning an engine is like upgrading a computer: all you do is shift the bottleneck. The golden rule with the B2x5 is to start with forged pistons and if the budget does not run to Verdi forged connecting rods, at the very least the connecting rods should be X rayed (or crack tested) then shot peened (to relieve stresses that may cause failures at higher revs) and then balanced end over end. A lightweight flywheel, competition clutch, crack tested, stroke-corrected, polished crankshaft with connecting rods and pistons should always be balanced as a rotating assembly. This costs serious money and there are relatively few shops in the UK capable of carrying out this work. Sceptics may question the logic of spending cash on jobs like crack testing or checking a crankshaft is perfectly straight but what is perfectly acceptable for a normal road car with maybe 250bhp will simply not do for a 400bhp road burner that may well run (with modified valve springs) a maximum rotational speed of 7000 rpm because the engine could literally fly apart.

B2x5 cylinder head component part numbers
Part SAAB Part Number Notes
Camshaft - inlet 55557273 (supercedes 9170887)  
Camshaft- exhaust 95499924 (supercedes 9188855) B205
Camshaft- exhaust 5955952 (supercedes 9170895) B235
Gasket: cylinder head 5960083 (supercedes 9171935 & 5960083)  
Gasket: valve cover (cambox) kit 8822041 Kit of x2 gaskets
Plug: core (frost) plug 7588320 5 per car
Plug: blanking 9135211 Blank for brake pump (manual)
Seal: valve guide stem oil seals 5955570 (supercedes 9170861) 16 per car
Valve: inlet 55560663 (supercedes 9185851)  
Valve exhaust 9399965 except Aero
Valve exhaust 9179219 B235 Aero only

 

 


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