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Our Classics

Our Classics: 1986 Ford Sierra RS Cosworth

by Jesse Crosse
18 January 2022 8 min read
Our Classics: 1986 Ford Sierra RS Cosworth
Photos: Jesse Crosse

At the wheel: Jesse Crosse
Owned since: July 2017
Current condition: Returned to original
Hands-on or hands-off? Hands on

Jesse Crosse started as a motoring hack in 1982, was launch editor of Performance Car magazine and signed up an unheard writer called Jeremy Clarkson. He now writes about automotive technology, and spends his time restoring a pair of fast Fords, a 1968 GT390 Mustang fastback, and the same Ford Sierra RS Cosworth long-term test car he ran while editor of Performance Car, reported on here.

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Being reunited with a car having parted with it 30 years earlier takes a bit of getting used to, especially when I’d become convinced that it had long since gone to that Cossie graveyard in the sky. But there we were, me and my Cossie, just like old times and good to go. Well almost.

Like most Sierra RS Cosworths that have led a full life (not the kind that have been squirrelled away to deteriorate in the name of future profits) mine had been tinkered with. That’s no surprise and like other true homologation specials built in limited numbers, the Sierra RS Cosworth was designed to be uprated.

Mine has very clean bodywork and you could eat your dinner off the underside. It’s been repainted, a front wing has been replaced, the colour is spot on, it looks great, and there is no sign of rust anywhere. Wheels are original and the interior appears to be the same one I sat in when it was new all those years ago. I collected the car on a trailer as the MOT had expired and began compiling a list of things in my head that needed doing sooner rather than later.

The front fog lights had been switched for RS500 grilles, a pity because those are unique to the 3-door Cosworth and rare. The plastic cam belt cover had been changed for an item of nasty chromed bling and the plastic radiator header tank had been changed for an aluminium one. The plastic air filter box (like the cam belt cover and fogs unique to the 3-door Cosworth) had also been replaced with a cone-type aftermarket filter.

The clutch clearly needed replacing as it was biting with the pedal close to the floor. The engine bay also had various other details that needed returning to standard too. The suspension had been lowered with stiffer coil springs and lowered MacPherson Struts, and there were a couple of aftermarket dials in the instrument panel where the digital clock and graphic display module normally sit.  

Once all that had been sorted and the Cossie returned back to standard trim, I planned to tackle the engine which had been given a bigger turbo, ported head, remapped ECU and larger capacity green injectors in place of the original standard yellow injectors. There was also the noisy matter of a large bore stainless steel exhaust which needed replacing with a standard one.

I was in the middle of a major restoration when the Cossie turned up, so I decided to get the initial bits and pieces sorted by a mate of mine, Richard Upton at ITG Motorsport. Richard had grown up rallying these things and knows them inside out, and once he’d done the basics and got the MOT renewed, I’d drive it around a bit and tackle the major jobs when I had more time. At least, that was the plan.

Ford Sierra RS Cosworth engine bay
Non-original parts shown above were replaced with genuine parts

So off we went. I set about sourcing the extremely rare air box and luckily Richard had a pair of fog lights and an original cam belt cover in his spares stock. I was able to get a new Helix clutch without any bother and we fitted a fresh pair of rear discs (they were the non-standard drilled-type, and one was cracked) plus new pads all round. The gear lever had been shortened for some bizarre reason and the gear knob, though standard, would twist annoyingly. Again, Richard had an original in stock so that was an easy fix.

While the clutch was being replaced, the gearbox was opened up and given a thorough check over. Finally, a new set of plugs went in and I’d already tracked a misfire under load down to a dirty harness connection in the engine bay. That was easily fixed by cleaning the contacts and administering a dose of electrical contact spray. With all those jobs done and the aftermarket dials replaced with an original clock and graphic display unit, the Cossie was already looking more like the car I knew and loved. Now all I had to do was drive it around for a bit and see how things shaped up, but as it turned out, I was in for a surprise…

13 December, 2021: The sound of an engine rebuild

Ford Sierra Cosworth engine rebuild_Jesse Crosse Hagerty

So far I’d already replaced a lot of the obviously non-standard parts on the Cossie so at least it was a lot more correct on the surface, but there was still a way to go to get everything just right. Like the huge majority of 3-door Sierra Cosworths the suspension had been lowered and stiffened and it had adjustable aftermarket shocks and struts. Although it looked cool it wasn’t how it should be and after a bit of research I found that all the replacement springs on sale for these cars are uprated and usually lowered too. The same goes for struts and rear dampers, so some research would be needed to find an original solution.

I also had to do something about the big bore stainless exhaust and I discovered once I’d got the car on the ramp that the rear anti-roll bar had been removed in order to use one of the mounting points to hang the exhaust at the rear. That was a daft idea because in standard form, the Sierra Cosworth inherently wants to understeer in slower corners and I could feel it seemed less willing to turn in than I remembered. The rear anti-roll bars may not be the beefiest but they do have an effect.

I had noticed that the engine sounded a bit tappety too, but on the Ford Cosworth YB engine that isn’t unusual. Cures can be as simple as replacing the hydraulic lifters and even changing the oil (and making sure it’s the right grade), but I’d already done that. Eventually I decided to remove the cam cover and have a look as the noise was irritating me. There was nothing obviously wrong but I thought I’d check the overhead cam bearing cap nuts were torqued down properly and when I did, one stud pulled straight out. That would explain a lot! In fact there were two stripped threads so that was that, I’d have to whip the head off and get it sorted.

While I was at it I pulled the plugs to check the compression and found one cylinder was a bit low. With a bore scope I could see the cylinder wall looked curiously pitted which was odd and something I’d never come across before. When the head came off I was able to see that the pitting was due to water damage from an earlier cracked cylinder head and it was clear that what had started as a brief investigation had now turned into a full rebuild. Luckily I’d already invested in an original Ford workshop manual (found on Ebay for £60) and had all the info I needed to make a start right away.

The engine came out easily even though the engine bay is less spacious than some older Fords because of the turbo and weirdly shaped exhaust manifold. After I had carefully stripped it down, I headed off to Steve Curzon of Vulcan Engineering based at Brands Hatch. Steve is an exceptional engineer who started in the engine building business as a lad, and his skill and knowledge of Ford engines in particular is second to none. The head would need the usual stuff, a very light skim to avoid head gasket leakage once back together, inserts for the two stripped threads and some work to ensure the compression ratio would be set to the correct 8.0:1.

The Garrett T3 turbo had been replaced with a bigger one to provide higher boost and would need replacing with an original Garrett T3 along with all the gubbins associated with that. The standard Mahle pistons had been replaced with Wiseco motorsport pistons and peripheral things like the larger intercooler, external venting dump valve, pipework, boost hoses and wastegate actuator would all need replacing with originals too. While the engine was at Vulcan having the machining work done, I set about tracking down a standard intercooler and the rare ‘Amal’ solenoid valve which both controls the wastegate actuator and acts as a dump valve to release inlet boost pressure when the driver lifts off the throttle. The next few weeks would be fun but the reassembly and setting up was going to require plenty of care and attention to detail to get everything spot on.

18 January, 2022: Cosworth specialists to the rescue

18 January, 2022: Cosworth specialists to the rescue

Although the Sierra Cosworth YB engine has its roots in Ford four-cylinder engines that had been around for a long time, the parts that make it what it is are pretty special. In standard form it’s a fairly unstressed engine at 201bhp (204PS), designed as it was to handle much more than that in motorsport trim. The important thing, as always in engine building, is to pay scrupulous attention to detail. In this case the ‘works’ workshop manual is very specific about detail, from the three different types of Loctite thread locker and gasket sealant that should be used, to the usual stuff like the correct tightening sequences, torques, assembly sequence, cam timing and more advanced things like the four Inconel bolts which attach the turbo to the exhaust manifold.

Inconel is a nickel-chromium-based “super alloy” designed for use in extreme temperatures such as jet engine turbines. It retains its tensile strength (resistance to stretching) even at extreme temperatures and must be replaced during a YB rebuild. It would be an easy thing to skimp on because of the high cost which comes in at over £27 each (compared to a few pence for a conventional high tensile bolt), but taking short cuts in engine building usually ends in tears.

I was able to track down an original 3-door Cossie intercooler in good condition. Similarly the Amal valve which controls boost, but some other things were a little more tricky and expensive to source. I found a firm that manufacture original spec boost hoses (two black, one terracotta-coloured) and they cost more than £175 for the three. A complete hose kit for the 3-door Cosworth would later cost a further £317, but the good news is, they were all factory correct. The original type hose clips are also available and all the old jubilee clips that had found their way on to the car over the years would be replaced with the variety of the proper jobs when the engine went back in to the car.

I was expecting that finding a Garrett T3 turbocharger would be tricky since they’re no longer made and secondhand turbos are bad news. If a compressor fails and the engine ingests bits then the result is catastrophic. Then I discovered Bernie’s Blowers in Essex. Bernie said he would build me a one from parts and he was as good as his word. Receiving it in the post a couple of weeks later was a highlight of the build so far; it looked as though it had come straight from the factory. Turbo-building requires great skill because they spin at a long way north of 100,000rpm, so the compressor and turbine assembly must be properly balanced.

I collected other bits, like the turbocharger bracket which was secondhand, but the fiddly turbo damper I was able to get new from Ford specialist Burton Power. The standard, yellow injectors were less difficult to find and I picked up a set tested and ready to go for a reasonable sum. The final, crucial element was to find an original Ford map for the ECU and the trail led me to Harvey Gibbs at Supreme Motorsport, in Peterborough. Harvey has been working on Sierra Cosworth mapping for decades and supplied a chip programmed with the original Ford code. By now, I had done loads of research and amassed all the bits and pieces needed for the engine rebuild. The next step was to nip down to Brands Hatch and fetch the engine parts from Vulcan Engineering which were ready for collection. More on that next time.

 

Sierra Cosworth fan? Bookmark this page as Jesse will regularly report on his Cossie.

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