How to ruin a rebuilt engine

So, on the very first drive after the engine rebuild I was gradually increasing the boost when I suddenly felt the power drop. A glance in the mirror and I couldn’t see anything behind at all but steam – the head gasket had failed in a big way. Cut the engine straight away, coasted into a lay-by and called the breakdown company.

Yup, that’s blown

Pulled the head, replaced the head gasket which had blown on cylinder 1 and she was running again, but making huge smoke once she started warming up. The compression was about 30% lower on cylinder 3, so I thought perhaps I’d cracked the head. Embarrassingly it was weeks before I realised that the smoke was because the rear silencer was saturated in coolant. Flushing it with a hosepipe solved it, but she still wasn’t running right – running lumpy at anything above idle.

I decided to instead concentrate on fixing a little hole by the right front side jacking point:

Eventually I decided I was going to have to pull the engine back out and tear it down.

The first ring had broken on piston 3, chewing up the piston and the bore and somehow also cracking the lower ringland?! To boot, even the bearings and crank are scored, presumably either from bits of ring, or perhaps I didn’t get every bit of crank sprocket.

The cause of all this? Turned out in my rush to get the car back together, I’d refitted the crank position sensor in the original position, not the one I worked out it should be in when I did the T5 conversion. So, the ignition timing had been 18 degrees too far advanced.

Currently I’m just waiting for the engine shop to reopen so I can find out what can be salvaged.


Saab 900 Engine Rebuild

With the engine bay sorted it was time to start on the engine rebuild. I bought an engine stand and mounted it up.

A quick clean up later…

Stripped and wrinkle painted a spare cam cover:

Stripped the engine down to find no visible head gasket failure, but pretty tired bearings.

The block, crank and head went to the machine shop where the head was skimmed, block honed and crank journals polished. New standard size bearings and piston rings were sourced, along with a full timing kit. The chain guides had to be sourced from Sweden at great expense. I had a spare later head from Erika that I considered fitting but learned that the later heads have a different combustion chamber which combined with my earlier pistons would reduce the compression ratio. Keeping the existing head meant sourcing new plastic nipples for the cam oiler tubes which the later heads don’t have. These tiny bits of plastic were really hard to find, and I ended up having to pay £80 for them.

Turns out early cam covers have a different sized rubber chain guide, which I was unable to source so I trimmed down a later one to fit.

Had a bit of a disaster during the rebuild. I’d fitted the head and the cams but not the cam sprockets, when for some reason I thought I’d fit the crank pulley. As the torque wrench clicked at 180nm I realised my error. I’d just turned the engine over without the timing chain connected. Assuming I’d bent some valves, the head came off to assess the damage but in fact the loose timing chain had bunched up and instead stripped the tips of some teeth from the sprocket. So, the only damage was a new crank sprocket, a new head gasket and another set of head bolts.

During this I dragged the supposedly good spare gearbox that came with the car out of the back of the garage. I’d never looked at it so was really disappointed to find it completely seized and basically ruined. Tried to free it off and eventually got the diff turning and gear selector working but still no drive, so £1500 later a freshly rebuilt box was sent from TR Autos in Cornwall. This box got a steel diff cover fitted to hopefully help it handle the power.

Didn’t get many shots to document this, but the original oil cooler was looking tired. Drop in replacements are really expensive, so after some measuring I bought:

  • Two M16x1.5 – AN6 adapters to go on the oil filter housing (use dowty washers on the M16 side)
  • A cheap 9 row AN10 oil cooler
  • Two AN10 to AN6 reducers to go on the cooler
  • And a few metres of AN6 braided line along with a load of fittings

The generic oil cooler dropped into the stock housing after some modification to the mounting tabs. A complete replacement for ~£100, instead of ~£280 for the DO88 kit.

The old standard Garrett T3 turbo was also pretty tired, and for the price of a rebuild kit I lucked out on a Chinese 60 trim T3. Turned out this was much bigger than the standard one! The standard hard oil drain and feed pipes wouldn’t quite fit, so I made up some flexible ones with AN fittings. To make the drain fit the block I welded a AN bung to the cut down stock drain, with a tab to fasten it to the gearbox bolts.

I also made a 3″ downpipe…

And 3″ intake pipework:

And that’s it! All back together.


Front suspension refresh

While tidying the engine bay, I’ve had all suspension components, engine brackets etc soaking in citric acid to remove the rust. This was my first time using citric acid and I was really impressed with the results:

Apparently the rally guys like to reinforce the lower wishbones, so I couldn’t resist having a go myself:

Cleaned up the aluminium wishbone mounting blocks and painted in the cheesiest colour possible:

And an obscene amount of money was spent on new old stock genuine SAAB engine mounts and Powerflex poly bushes.

Saab 900 engine mounts

And finally, painted with POR-15.


Engine bay welding

Since pulling the engine out, progress has been a bit slower than I’d hoped during lockdown but I’ve still got a fair chunk done.

The right driveshaft tunnel has had a repair patch before but now the arch above was pretty thin…

Then I cut out the battery tray since I’ve relocated it to the other side (before realising I could have simply unbolted it) which revealed quite a lot of thin metal. Decided I’d be best to cut out the box crash structure to do the repairs, so took a lot of measurements and did this:

There were a couple of other patches around the bay, such as the front crossmember:

You can see here the angle iron added for strength where metal was cut away for the front mount intercooler.

After that, time for paint!

I’ve also coated the underneath and arches with Bilt Hamber Dynax UB, which is a thick black wax, and injected their Dynax S-50 wax into the box sections, which is a much thinner consistency.


Lockdown rebuild

So, just before lockdown, I found a little more sludge on the coolant cap. Out came the borescope…

Funnily enough a compression test turned out fine – in fact 2 and 3 had slightly more compression. I guess the water was helping the rings to seal.

Anyway, since I couldn’t go anywhere anyway, why not turn it into a much bigger project! So, engine out:

Saab 900 engine

Doing my first full engine out on my own was a bit scary, but it came out fine with the only casualty being one of the oil cooler line unions to the oil filter block which sheared instead of unscrewing. That’s a problem for later. I’m not decided how far I’ll go on the engine rebuild yet, at the very least I’ll replace all seals and gaskets plus sort the inevitably broken exhaust studs

The plan is to strip the bay, sorting any rust (so far 95% of it is just surface so that’ll be treated with a wire wheel and Deox gel, though there’s a couple of tiny patches needed), cleaning and repainting the wishbones and replacing all bushes plus the steering rack will be swapped for a hopefully less leaky spare.

The upper wishbones were a real pain to remove because most of the bolts sheared thanks to galvanic corrosion between the bolts and the aluminium mountings. Luckily they all sheared at the head leaving some stud that I could unwind from the captive nuts at the car.

Next step, welding!