Headgasket repair on my 1986 8v carburettor 900

Matthew · Dec 11, 2005

The headgasket on my 1986 8v carburettor 900 started to let go on Sunday last week. The car was still very drivable until Thursday morning this week when it was misfiring badly until the engine heated up. I didn't use it after that.

I have for a couple of months now been suspecting that the headgasket on my 1986 8v carburettor 900 was thinking of letting go. No obvious symptoms though, just gut instinct. The car had not been used for around six months, which is always bad for a headgasket that's probably got 200,000 miles on it.

The car began to develop symptoms of headgasket failure last Sunday when I fitted a different (aftermarket ;oops: ) higher-rated thermostat as an experiment. The car had been running too cool for my liking in this cold Winter weather and the heater was rubbish. The previous thermostat was an 82-deg, and the new an 88-deg Calorstat.

While driving to see a friend after installing the thermostat, the temperature gauge suddenly shot up to nearly on the red. I stopped the car, the temperature gauge continued to rise for a while but then plummeted to normal levels. It looked like the thermostat had stuck shut.

I realise now that my mistake was not bleeding the cooling system after installing the thermostat. It's possible that a pocket of air behind the 'stat preventing it from reaching opening temperature, while the coolant boiled.

I drove the car home and fitted the original, Saab thermostat. However, the temperature gauge still shot up suddenly to max, before falling rapidly to normal.

A couple of days later, the engine began to mysteriously lose coolant - around 1 litre a day. If I kept the cooling system topped up, then the car would run fine and temperature remained normal (apart from the odd hiccup to max).

All through this time the oil was clean, apart from a little mayo on the inside of the dipstick tube. The car drove fine, but idle was lumpy and erratic.

As of Wednesday, the car started churning out a lot of steam and developed a bad misfire when cold. That's when my strong suspicions of headgasket failure were confirmed.

I rely on this car to get to my place of work 25 miles away, and so needed to get it fixed this weekend. I ordered parts (including new head bolts)and began work this (Saturday) morning.

The radiator is also shot (see later) and so I decided that I had to replace that too. I also bought a genuine Saab 89-deg thermostat for the colder weather.

This thread isn't intended as a how-to, but just a few pictures and my own thoughts from doing the work today.

I decided to remove the bonnet to give myself more space in which to work. A few pictures of the engine bay before I started (mainly for my own reference). Hopefully this is how it'll look by sunset on Sunday:

After I removed the bonnet, I also removed the battery to give myself more working space in the engine bay.

First up was to drain the cooling system, including the block. This is my most hated job as it always ends up being more messy than necessary.

I found some old cooling system hose to connect to the radiator's drain. Plan was to remove the drain plug and pop the hose on straightaway.

I poked the other end through a conveniently placed hole in the chassis.

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

The other end drained the coolant into a container underneath the car. The coolant looks in good condition, but I'll replace it with fresh.

Now to drain the cylinder block. You need to do this otherwise the cylinders will end up full of coolant when you lift off the block. In fact, there's so much coolant in the head that it'll drench everything and also end up in the oilways. I can't understand why most folk don't drain the block.

Everyone has difficulty finding the block drain plug (maybe that's why they skip this bit!). It is hidden away behind the exhaust manifold. It's not too difficult to remove on a T16 though, but bloody murder on a NA 8v.

The plug is usually seized up and spanner access is dreadful. I used a deep socket (15mm IIRC) and a breaker bar to crack the plug, and then a ratchet and socket for the rest. Be warned though - the first time I used the breaker bar for this on an 8v, I shorted out the battery with it (me and electrics).

Anyway, the plug assembly's almost in the centre of this photo, directly above the driveshaft and bolted to the block.

The plug is not the largest - that's for fitting a block immersion heater. The drain plug for the block is the rusty-heated bolt to the right of the big one.

I have not yet found a way to contain all of the coolant that gushes out of the block when the plug's removed. A container placed below the plug is the best you can hope for.

I replaced the plug with a dab of copper grease. Don't overtighten it as engine heat will tighten it up anyway, and it'll be impossible to remove next time.

With the cooling system completely drained, out comes the radiator.

Now, I inspected this radiator only a couple of months ago and it was fine, no leaks or missing fins. It looked likely to need replacing within the next year.

However, as you can see, the radiator's completely shot. Suddenly the thing's started to disintegrate. The fins en masse have become detached from the waterways. Tapping the rad is enough to send a shower of fins to the ground.

I reckon that it'd have lost all its fins within one week further driving.

Interestingly, this radiator was re-cored by the previous owner. The end-tanks are metal (brass I think), unlike today's radiators which are plastic.

The radiator I bought turned out to ne a Nissens unit.

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

Old and new rads together.

The mountings for the old rad are different to the new rad.

Mounting point for the fan thermoswitch. Note the plastic end-tanks crimped into the frame of the rad.

The Nissens radiator is sooooo much lighter than the old radiator, and the matrix is made from aluminium instead of copper. The new radiator is very much thinner than the old one, perhaps only two-thirds as thick.

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

I'll wait until I have finished the cylinder head gasket job before I install the new radiator. I don't want to damage it, and having it out of the way gives more workroom.

Back to the head then. Off comes the cam cover. Interestingly, on the 8v cars the distributor's bolted to the camcover and not the cylinder head. It's driven by a dog that engages with the cam. To remove the cover, the engine must be at 0-degrees TDC so that the dog's vertical and can be lifted up from the cam.

Before removing an 8v H-engine head you must wedge the timing chain against the tensioner. These engines have an internal tensioner, unlike the 16v H-engines which have the removable external tensioner.

On a 16v H-engine you remove the tensioner assembly before lifting the head, but that's no possible on the 8v H-engines.

When the cam sprocket's removed, the chain becomes slack and the tensioner will extend to its maximum position. Retracting the tensioner would mean removing it, which means removing the timing cover, which means removing the engine!

I was quite nervous about wedging the chain, as if it went wrong and the tensioner extended then this car's effectively scrap. No way am I removing the engine to sort out the tensioner.

I tried various ways of wedging the tensioner, and eventually used the wooden handle from a file. I gently tapped the handle inbetween the chains.

You have to choose something that will be secure between the chains, but which won't get in the way when you lift and then reinstall the head. The wedge device has to be out of the way, as it could get knocked and might then fall out.

BTW - I tightly tied a tether to the handle so that if it did fall down into the crankcase, then I'd be able to retrieve it.

I must thank nutcase for telling me that the tensioner had to be wedged. I'd previously thought that all H-engines had the external tensioners!

So here we are with the cylinder head removed. Notice that cylinder one is at the top of its firing stroke. See the wood wedged in between the bottom of the gearbox casing and the two braces underneath the engine bay. That's to take the weight of the engine when the right-hand engine mount stay is removed.

You can just see the file handle underneath the cam sprocket. Also note that I cable-tied the sprocket to the chain, as I didn't want to faff around with the valve timing when I refit the head.

A closeup look at some of the headgasket waterways. This first one is on cylinder one, showing where the gasket failed. The waterway on the top-left is gone through to the combustion chamber sealing ring. The waterway on the bottom is almost as bad.

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

In fact, most of the waterways were quite ropey. The apertures had really opened up, and the gasket in those areas was disintegrating.

These marks are I think the original cylinder hone marks. I confess that they do look more like stratches, but I'm hoping they're the hone marks - not bad for an engine with en estimated 300,000 miles!

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

The cylinder head on the bench. You can see that I decided to lift the head complete with exhaust manifold. I am now sure that this was the right move, as at least three of the exhaust manifold studs are inaccessible without removing the heatshield, which would probably disintegrate in the process. I am also sure that at least one of the studs would have snapped, and I don't have replacements.

The mating face of the cylinder head before cleanup. Cylinder one is on the left, four on the right. Note the mechanical fuel pump mounted bottom-right, as fitted only to the carburettor NA 900s.

Chamber four. All chambers were quite coked up. Anyone know why all the exhaust valves (apart from number one) are white? That stuff's a white/cream hard deposit.

Chamber three. Some signs of deterioration to the gasket around the waterways.

Chamber two. More deterioration. I was wondering what the radial marks around the chamber were (where the sealing ring'd sit).

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

Chamber one - where the gasket blew. Clearly this is a different colour to the rest, and indeed the inside of the chamber was wet with coolant. Notice the scab of pitting to the left.

Closeup of the pitting. It's quite bad, and ideally the head would be skimmed.

I then cleaned the head. I used a metal decorator's knife/scraper to remove the glued-on bits of gasket, being very careful not to scrape or nick the soft aluminium material of the head.

Then I cleaned the head thoroughly with white spirit, and used a soft wire brush to remove some of the coke deposits from the chambers.

I then used 400-grit on a sanding block to flat-down the head. This didn't actually remove any metal, but the remains of the gasket, rust and limescale deposits. I followed up with 2000-grit.

Finally, I cleaned the head thoroughly again with carb cleaner.

A closeup of the pitting, after cleaning. I cleaned this area with brake cleaner, as it leaves no residue.

Now, if I was a bit richer and didn't need this car for work on Monday morning, then I'd have stripped the head and taken it for machining. However, circumstances mean that I can't do that and must repair the head myself. Luckily I have tubes of JB Weld already.

I applied the weld with the same knife/scraper I used for cleaning up the head (after cleansing it with brake cleaner). I then carefully pressed the weld into the pitting, leaving an almost flush finish.

Tomorrow, when the weld's cured and hardened, I'll flat it down with some fine paper (probably 400-grit again). I brought the cylinder head inside the house so that the weld would cure - the temperature inside the garage is too low for the weld to cure in time for reassembly tomorrow.

Now to cleanup the block. This is the block after I'd removed the old gasket.

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Matthew · Dec 11, 2005

Headgasket repair on my 1986 8v carburettor 900, continued...

Closeups of the waterways shows rust, but actually barely any pitting to the block's deck.

The block face after cleaning.

I used exactly the same procedure on the block as I used on the head - scrape, brush, clean, 400-grit, 2000-grit, clean.

In fact, in the photo above I'd not yet cleaned thoroughly the cylinders. A fair amount of rubbish ends up inside them, so you must take care to clean them out.

Found this stamped on the block - I wonder what it means?

I have also changed the oil (which was clean) and filter.

Blimey... that turned into another epic post. Wasn't meant to!

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Dean O · Dec 11, 2005

trying hard not to be overly 'gushing' here, but utterly in awe of knowlege & skill & admiration of 'devotion to duty' - major (potentially risky) job on a tight deadline & you still find time to detail & photo every stage

fingers crossed for the pitting repair

didn't gush too much did I?

deniss · Dec 11, 2005

Wow Matthew. Just wow.

Excellent pictures and commentary, as always. Very nice tips on how to clean and "resurface" the head. Good luck getting it all together. Seems like you've had decent luck taking everything apart! :cheesy:

900t · Dec 11, 2005

I've always wanted to see what that looks like on an 8v. I've already seen T16 and 16i's in my own experiences, so hey...

Jezzadee · Dec 11, 2005

{Doffs cap}

Another superb write up. Even I'd be happy having a go at it armed with this.

RoccoH · Dec 11, 2005

Nice one Matthew! good luck with finishing up this one!

hope you'll like my soon to be executed driveshaft/head gasket/engine out/timing chain overhaul report as much as I like your write-up

Si · Dec 11, 2005

I hope this thread is going to be around for a bit, i think i'll be doing this in the new year.Nice write up Matthew

James Bond · Dec 11, 2005

Absolutely brilliant!

nutcase · Dec 11, 2005

Matthew said:
I must thank nutcase for telling me that the tensioner had to be wedged. I'd previously thought that all H-engines had the external tensioners!

Just passing on what was told to me by John-w when I was doing the head on Blu'y

Another quality write up BTW

When the cam sprocket's removed, the chain becomes slack and the tensioner will extend to its maximum position. Retracting the tensioner would mean removing it, which means removing the timing cover, which means removing the engine!

I was quite nervous about wedging the chain, as if it went wrong and the tensioner extended then this car's effectively scrap. No way am I removing the engine to sort out the tensioner.

I *think* you can reset it with a small flatblade screwdriver and a bit of cunning. Obviously a lot better not to have to though, but taking the engine out isn't necessary.

ShadowWorks · Dec 11, 2005

What a terrible write up, poor pictures, poor explainations and you know I am talking rubbish:cheesy:

Once again you should be writting a book on the classic 900 Matthew you have just knocked ten bells out of Haneys Manual and battered Bentleys as well:lol:.

You keep pushing the bench mark for quality informative threads Matthew, thank God you dont drive a BMW

ejenner · Dec 11, 2005

Sometimes when draining the block it is much eaiser to remove the three bolts that hold the drain-plug assembly to the block. Obviously if you do it this way then you will need a new gasket and you will also have to clean off the old gasket. The drain-plug assembly is a part that often needs to be replaced (my local specialist keeps them in stock) They rust badly on the inside I guess because a small amount of water always sits in the downward angled assembly and the heat of the engine causes the corrosion after the engine has been shut-down and the water has stopped circulating.

Did you fill with 100% coolant or coolant/water mix? and did you use distilled water?

Matthew · Dec 11, 2005

Thanks folks

I usually don't start out intending to write such mammoth posts, but one thing leads to another.

I'm just in after another day's hard work. The car started first time, but had some worries with the head bolt torquing procedure. A call to nutcase later, and things *seem* to be okay - fingers crossed.

I have some more photos, but right now I'm too knackered to write them up! :lol: Going to buy fish and chips, a bottle of wine and then have a bath!

nutcase said:
I *think* you can reset it with a small flatblade screwdriver and a bit of cunning. Obviously a lot better not to have to though, but taking the engine out isn't necessary.

Reading through the re-fitting instructions in Haynes today, there's mention of being able to access the ratchet's pawl with a screwdriver to adjust tension. Great news then that it's not a disaster if the wedge falls out.

ejenner said:
Did you fill with 100% coolant or coolant/water mix? and did you use distilled water?

50% antifreeze (Comma XStream Green) and 25% distilled water, 25% tap water. I would have used 50% distilled water if I'd not run out :roll: :evil:

Forgot to mention in my original posts - after removing the block drain plug, nothing came out. I assumed it was blocked to dug around gently with a screwdriver and then coolant pissed out everywhere :lol:

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William A Yelton · Dec 11, 2005

I just had mine replaced at Sovereign Saab in Atlanta Georgia. It was by NO means inexpensive but they updated a Lot of other items,checked out my Turbo thoroughhly and really updated everything while they were in there. As I have had my Turbo 900 since she was new time and cost is NOT an OBJECT at all. I LOVE MY 900 TURBO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!:cheesy:

COST WAS WELL WORTH THE IT

ejenner · Dec 11, 2005

Forgot to mention in my original posts - after removing the block drain plug, nothing came out. I assumed it was blocked to dug around gently with a screwdriver and then coolant pissed out everywhere

as well as the rust it seems to be a catch point for particles in the coolant system, crud sits in the downward facing drain plug. Probably helps it not work properly.

Jezzadee · Dec 11, 2005

William A Yelton said:
COST WAS WELL WORTH THE IT

How much did they charge?

Alex · Dec 13, 2005

Excellent write up.

Interesting that you have to wedge the chain on the H-series engines.

The B-series has a locating arm that the sprocket attaches to when it is removed from the cam to maintain the tension in the timing chain.

ejenner · Dec 13, 2005

It also has two timing chains as well ! or so I've heard...

nutcase · Dec 13, 2005

Alex: Yup

I guess cost cutting got rid of it for the H.
Ejenner: Almost - it's a duplex one.

Tomarse · Dec 13, 2005

Matthew said:
Reading through the re-fitting instructions in Haynes today, there's mention of being able to access the ratchet's pawl with a screwdriver to adjust tension. Great news then that it's not a disaster if the wedge falls out.

You really dont have to wedge the tensioner on the H engine. I havent done on either of the cars ive done (including the 900T back in august). It's not going to hurt though!

There is a little release on the tensioner itself which will release it so you can pull the chain up and move it back in. You can get at it with a tiny screwdriver or a bit of welding wire (not mig wire a proper stick).
It really isnt that hard to do. If you have a good look at it while the head is off you can work out what you are doing.

Headgasket repair on my 1986 8v carburettor 900

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