June 2010: Photos of some stages of removing and renovating a 16 valve cylinder head from a Saab 900i Classic (1992 model year). As of 2015 the car was still running beautifully. It was taken off the road for a couple of years and then sold with a new MoT in May 2018. If you were the lucky buyer of this car the reg number was K62 KFG.
The fault on this car was that, after 204,000 miles and 18 years, the head gasket was exhibiting chronic (albeit minor) external oil leakage. More recently, there had been some leakage of high pressure oil into the coolant system. This latter symptom is usually the prelude to total failure of the head gasket - which can allow water into the oil. In extreme cases, and when owners continue to drive knowing or suspecting that something is seriously wrong, the engine can be destroyed.
Head gasket failure is particularly common on some engines, for example the K series model used in some Rover and MG cars. In the Saab 900, head gasket failure usually occurs only after 200,000 miles or 10 or 15 years. The Saab 1985cc engine is a robust unit, having been in production for over 40 years but suffers from the generic problem of all cast-iron/alloy head designs - there is considerable movement between the block and the head as the engine heats up and this has to be accommodated by the head gasket. The number of heating cycles is therefore important, and this is one reason why cars used mainly for lots of short journeys can suffer head gasket problems at relatively low mileage.
In this particular case (fingers crossed) the engine may have been saved from any significant damage because it was dismantled when symptoms first appeared, and long before water started to get into the oil. The total cost of repairs (parts only) was less than £100. Garages charge typically £500 to £600 just to renew a head gasket - and without all the careful and time consuming work of valve grinding and cleaning up the surfaces properly.
I originally purchased this car for £300 in March 2007 via an advert on ebay. Apart from a thermostat (£6), a new key (£4), and routine replacements of brake pads, fluids, oil etc, it has given little trouble over 25,000 miles. The clutch was replaced (with one from a scrap-yard) and has been OK ever since. The only serious problems upon acquisition were the thermostat, failed bottom suspension ball joints (despite having just passed an MoT at a Saab garage), and a leaking clutch slave cylinder. The total cost of these repairs was around £25 - some bits being obtained from scrap-yards. I sold the car for £1000 in May 2018, with a new MoT!! It was driving very well at the time.
The weak points on Classic Saab 900s include the steering rack which can suffer from 'Saab morning sickness' (SMS) and the gearbox. Whilst repairing a steering rack can sometimes be feasible, replacing a badly worn gearbox is usually uneconomic even as a DIY proposition. Most 'classic' Saabs are scrapped because of either rust or gearbox or other 'major' faults which renders them uneconomic to repair at garage prices. The bottom ends of the engines are capable of lasting for 800,000 miles or more - if properly maintained. The top ends can last a similar mileage but head gaskets usually start to fail at around 200,000 miles.
The following photos show some key stages of the work -spread over the best part of 8 days. On simpler engines - those with a cast iron head, ordinary tappets and only 8 valves, so little can go wrong that the work is straightforward and almost risk-free. On a 16 valve light alloy head with hydraulic tappets, any mistake, especially scoring of one of the tappet bores, can render the head useless. Even dropping a steel tool onto one of the critical surfaces of the light alloy head can produce irreparable damage
Warnings are given about errors in the Haynes workshop manual for this vehicle.
|In the beginning ..... the
exhaust manifolds have been removed and the exhaust pipes taped up and protected by layers
of supermarket bags (just visible at the bottom of the photo).
On engines with a cat (catalyst) it is important not to allow debris or fluids to fall down into the exposed exhaust pipes.
Spark plugs were loosened but not removed at this stage. The inlet manifold with the fuel injectors is still attached to the head.
|The engine and gearbox have
been jacked up so that the top part of this engine mounting could be removed. This enabled
the exhaust manifold to be removed.
The engine and gearbox assembly was supported by a block of wood jammed between the gearbox sump and the alloy cross member.
The power steering pump was now visible behind a part of the offside engine mounting. This was covered in oil and grime - but the oil was from the leaking head gasket, not from the PAS pump itself.
|The top cover, before cleaning
and before the old rubber gaskets were removed.
The hard rubber 'top rubbing block' for the timing chain can just be seen.
|Top cover (camshaft cover)
Oil was vacuumed out from pockets in the head using a DIY tool - a thin plastic tube, an old paint tin as a reservoir and a vacuum cleaner.
It was important not to let debris or any small tool fall down into the timing chain - if it could not be retrieved the entire engine and gearbox would have to be removed to strip off the front of the engine.
Clean (and empty!) supermarket bags were stuffed down amidst the chain to block off the passageway.
|Removing the cylinder head
bolts required probably 300 ft-lb of torque - more than this cheap extension bar could
Never buy cheap tools!
|The old cylinder head gasket,
before it was removed from the block.
Old newspapers were used to catch stray oil - and with one particularly appropriate headline in view!
This was an article about repair of domestic appliances - instead of throwing them away.
|The cylinder head after removal
(complete with camshafts), showing the hard carbon deposits on exhaust valves (top row)
and the residue from the old head gasket.
It takes about half a day properly to clean up a cylinder head, after which the valves can be removed and any necessary grinding undertaken.
At this stage, extreme cleanliness is not necessary - that comes later.
|Camshafts removed. It is
essential to keep tappets and valves in their correct order - all 16 of them. Inlet valves
1 to 8 at the top, exhaust valves at the bottom.
A xylene based felt tip pen (impervious to paraffin) proved a great asset. After degreasing, the same pen was used to mark the tops of the hydraulic tappets before they were removed (using a magnet).
|Old kitchen cupboards destined
for the scrap-tip found one last use - as storage units for various parts. Once the boxes
were empty then everything was known to have been reinstalled. Various bolts were labelled
- so I knew where everything came from.....
The two camchain sprocket wheels are shown. Sprockets and a reliable chain are the alternative to a cambelt - used on most modern cars because of cheapness and ease of assembly in factories.
|The head in position on a
workbench ready for the inlet valves (lower set) to be ground in.
It is easy to grind a valve into the wrong seat - so everything was numbered to minimise the chances of a mistake.
|The cylinder head after all
surface finishing and valve grinding was completed.
It was now ready to be finally washed with paraffin and pressure hosed.
|The faces of the exhaust side
after final cleaning and surface smoothing.
These surfaces are not critical and can if necessary be 'bodged up' using exhaust sealant.
Like the rest of the head, these surfaces were in remarkably good condition after 204,000 miles and 18 years.
When years later I sold the car it had done more than 232,000 miles.
|The critical surface of the cylinder head, after final washing with paraffin and high pressure hosing. All steel surfaces and valve guides and inserts were dried with paper towels and the excess water vacuumed away - a job made easier in the strong afternoon sun.|
|Close up of valve seats for
cylinder 4 - nearest the front of the car.
There are small areas of minor corrosion on the face of the head but nothing too serious.
Years of experience is the best guide as to what you can get away with.
|Cylinder 1, timing chain end
(front of engine but to the rear of the car).
The main oil pressure feed to the cylinder head can be seen. All the oil ways in the head were flushed through with paraffin - which was then vacuumed out.
This was a little risky because the vacuum cleaner could have developed a mildly explosive mixture of paraffin vapour and air - and be ignited by the sparks from its commutator motor.
|16 valves, ground in, cleaned
When storing valves in this way - only ever remove one at a time, even if they are numbered! If they are mixed up they have to be reground, and it is important to grind in the valves in this engine as little as possible.
|The first valve to be
reinstalled - number 8 exhaust, one of the valves serving cylinder no. 4.
Only 15 more to do!
A close-up view of the tappet bores is shown in the next photo.
|There are 16 of these highly
polished and critically machined bores - in which the hydraulic tappets operate.
Any damage to these surfaces can render the whole cylinder head scrap. A special tool is used to slide down these bores to protect the surfaces from scoring when a valve spring compressor is used.
The proper tool is a Saab part (not sold to retail customers) so as a substitute, a section of thin wall Waitrose drinks bottle was used. It worked perfectly.
|The valves in this head are
deeply recessed. An extension to the valve spring compressor was effected by using a brass
nut from an old 15mm plumbing fitting.
The tappet bore is protected by a thin but tough plastic sleeve - made from an old drinks bottle - see next photo. It cannot be seen in-situ in this poor quality photo.
Damage to the bores could render the hydraulic locking action of the tappets inoperative - so the valve clearances would not be correct and the engine would be very noisy.
|These 250ml drinks bottles are
ideal for use as tappet bore protectors.
Sold by the innocent drinks company in 'hard' PETE plastic (that keeps its shape well) they can easily be cut to length with a sharp knife.
It is best to remove all traces of the paper labels.
The company says it is interested in alternative uses for its bottles - this must be one of the most unusual.
|Re-inserting valve collets is a
tricky job when the valves are deeply recessed. It is critically important to get this job
Gravity is a useful aid, and the head has to be suspended 300mm or more above the ground, allowing room for the spring compressor. An old kitchen cabinet proved an excellent workbench.
|The block surface after initial
The faces of the inlet manifold are yet to be cleaned.
The brass plug shown centrally in the manifold is the temperature sensor for the engine ECU.
|I had to buy a new one of these
for my older 8 valve Saab (1985 vintage). It is the aluminium drain plug housing for the
cylinder block and is usually almost inaccessible beneath the exhaust manifolds.
Remarkably, this one was in excellent condition - and with no sludge in the waterways having collected at this low point, signifying that the coolant had been kept to strength and that there had been no serious leakage of exhaust gases into the coolant.
These were encouraging signs.
|The timing chain shown bunched
up and ready to be encased in sticky tape while the head is replaced onto the block.
At the slightest movement the oily chain would slide all the way out of the engine - so you had to start over again ledging it into place.
The top chain guide is pivoted, while the lower one is fixed. On these later engines a more sensible design of chain tensioner is used - earlier models were more difficult to dismantle.
|A supposedly difficult part of
the job is reinstallation of the cylinder head over the camchain guides.
Here the guides are held together (neatly out of the way) and the chain is bundled up and held in place by sticky tape. The tape had of course to be removed as soon as the head was in place - and before the adhesive gripped too strongly on the clean metal surfaces.
This proved an easy method of holding the components in place - according to 'the book' you need an assistant.
|The new head gasket in
A stud made from an old cylinder head bolt with its head cut off has been inserted to the lower right - the head was then located on this and simply swung into place clockwise over the timing chain assembly.
|The cylinder head ready to be
assembled back onto the engine block.
It was given a final surface clean using a powerful degreasing agent, after which the surfaces were not touched, even with clean hands.
|Fully assembled and with the
head bolts tightened down progressively to 40, 50 then 60 ft-lb torque and then rotated
through a further 90 degrees using a metre long extension bar (and praying the new bolts
To achieve a 90 degree final torque loading, the tops of the bolts were dabbed with white paint after the 60 ft-lb tightening, and each was then rotated in turn a further 90 degrees - give or take maybe 5 degrees.
One of several errors in the Haynes workshop manual for the Saab 900 is the advice to bolt down the cylinder head with the pistons still at TDC (Top Dead Centre). Had this been done, the engine would have been destroyed. The reason is as follows: when hydraulic tappets are stored in an oil bath during engine disassembly, they seem to expand and suck in more oil. When reinserted into the head, the camshafts must be rotated several turns to allow the tappets to settle to a normal running clearance - only then will the amount of valve lift not be excessive. It is ALWAYS to be recommended that cylinder heads be bolted down and camshafts rotated to settle in any hydraulic tappets while the pistons are well away from TDC (i.e. a good inch below the top of any bore).
I discovered the problem as follows: having made sure the pistons were well away from TDC as the head was bolted down (which I thought was obviously a good idea!), I brought the camshafts to exactly their TDC position and then tried to rotate the crankshaft back to TDC in order to align everything ready to install the timing chain. The crankshaft stopped just short of TDC and refused to budge - obviously a valve had contacted one of the pistons and was jamming the engine. The cure was to rotate the crankshaft back away from TDC (reverse direction of rotation), then rotate each camshaft several turns to settle in the hydraulic tappets (this presumably permitted any excess oil within the tappets to escape), whereupon the crankshaft could now be turned to TDC when the camshafts were once again set at their TDC positions.
Thus, the engine could now be reassembled safely. With the camshafts driven by the timing chain the engine was gently rotated several times to confirm that all valves were clearing the pistons at TDC of all cylinders. If care in this part of the engine rebuilding had not been exercised (or if the instructions in the workshop manual had been followed unthinkingly), the engine could have been destroyed.
This is what happens when either a timing chain snaps or (with most engine designs) a timing belt snaps. Valve(s) then crash into piston(s), bending the valves, possibly damaging the pistons and in effect destroying the engine. Cambelts should be replaced at recommended intervals to help avoid these disasters. Often, belt driven water pumps and tensioner pulleys have to be replaced also and the job can cost £600 or more on some engines. The ancient design of the Classic Saab 900 engine has no such problems and breakage of the timing chain is almost unknown. The chain cannot be renewed without removing the entire engine and gearbox, so most owners just change the oil regularly and hope for the best. It is possible however to renew a chain by splitting it and gently threading a new one down into the engine, linked in to the old one. This procedure obviously leaves the new chain with a 'removable link' in place, which is a weak point in itself and may be best avoided.
Some engine designs are 'non-interference', a term used to describe a design in which the valves cannot ever hit the pistons, even if the chain or belt does snap. Some Fiat FIRE engines are this design - and are also distinguished by being manufactured in plants in which there are no human workers - only robots. (FIRE = Fully Integrated Robot Engine).
Some BMW engines (and all Mercedes) use timing chains and again, breakage is uncommon but not unknown. A garage told me recently they had mended a 5 year old low mileage BMW which had snapped its timing chain - the repair bill was over £4000. Timing belt engine designs are nowadays gradually being phased out, such are the problems and poor Press that they have generated. Likewise, dual mass flywheels have proven to be a disaster (costing over £1000 to replace and sometimes at low mileage). They were introduced to help smooth out the 'knocks' associated with high performance common rail diesel engines but nowadays, engine electronics are taking over the 'antiknock' and engine torque smoothing functions and solid flywheels are being reintroduced - as in the Classic Saab 900 these can last reliably for in excess of a million miles.
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