Epic Restoration – Mercedes 300SL Gullwing

‘You don’t really expect a £211,000 Mercedes Gullwing to be a death trap’

The road-going 300 SL evolved from the 1952 Le Mans-winning racing car. Its complex construction makes renovation tricky

The road-going 300 SL evolved from the 1952 Le Mans-winning racing car. Its complex construction makes renovation tricky

Words Nigel Boothman Photography Laurens Parsons

When Tim Jones bought this 1955 Mercedes 300 SL Coupé unseen at auction he had few worries. The car was described as roadworthy and in nice condition, and it did indeed look tidy. But all was not well underneath that luscious steel shell. In fact the ‘nice’ Gullwing ended up needing a full and exhaustive restoration.

‘After the second or third breakdown I thought it was time to get it sorted properly,’ says Tim, from London. ‘I was given Mototechnique’s name by a friend soon after I bought the car, and I think I fell on my feet there.’

Kevin O’Rourke of Mototechnique sent one of his team to bring the car back to the workshop in May 2010. He took it easy, but at one point had to brake hard in heavy traffic. ‘The Gullwing shot across the road,’ says Kevin. ‘The brakes were effectively working only on one side and he had to correct like mad to avoid an accident. The thing was a death trap.’

The mechanic also heard a suspicious noise from the transmission so, after rebuilding the brakes, Mototechnique removed the gearbox, revealing that the flywheel was cracked and the gearset and gearbox bearings needed replacement. 

Gearbox fresh from the car before being rebuilt using gear clusters from the Roadster, giving taller ratios for more relaxed cruising

Gearbox fresh from the car before being rebuilt using gear clusters from the Roadster, giving taller ratios for more relaxed cruising


Shortly afterwards they discovered a silted-up fuel tank and a failed injector pump. Kevin O’Rourke phoned Tim to relay the news and soon realised he’d reached a tipping point: ‘Enough is enough,’ said Tim. ‘Just go through the car and do it properly.’ He also discovered the car’s original colour was black not silver . ‘So I went for a repaint and retrim too.’ And so began a full restoration. As Tim says, ‘It’s such a great car that it deserved to be done right.’

Chassis & bodywork

A lack of structural integrity will spell catastrophe
— Kevin O’Rourke

‘It was a nerve-wracking moment when the Gullwing’s bodyshell had to come off,’ says Mototechnique boss Kevin O’Rourke (left). ‘It had to be lifted at the rear and then moved forward to “unhook” from the end of the chassis, which tucks inside the nose section. Any lack of structural integrity in the shell could have spelt catastrophe. Luckily it came apart without drama and we tack-welded the shell to a specially constructed frame, ready to be transported to the blasting firm.’ 

Gullwings are susceptible to coats of Teutonic-looking silver paint in the same way that Ferraris often pick up layers of ‘re-sale red’ as they pass from one owner to the next. As Tim Jones’s car had originally been black, the team wondered how many re-sprays had been done since then, and what they would conceal.

One of the riskiest operations was lifting the bodyshell off the tubular chassis. If the body was rotten, there was a risk it could bend under its own weight. Fortunately it didn’t...

One of the riskiest operations was lifting the bodyshell off the tubular chassis. If the body was rotten, there was a risk it could bend under its own weight. Fortunately it didn’t...


‘This is usually the point in a project where even our worst fears are exceeded and budgets for the finished job shoot upwards,’ says Kevin. ‘In this case Tim got lucky, perhaps deservedly, considering that he thought he’d bought a nice roadworthy example.

‘The chassis also turned out to be in surprisingly good condition, with none of the narrow tubes needing replacement. But because it forms the basis for the car’s dimensional accuracy we checked it in-house for straightness on our 3D jig. 

‘We chose soda-blasting to remove the paint and rust from the bodywork. I don’t trust chemical dipping because it can be harsh and too much material gets removed. Also, the chemicals get into every seam, and I don’t believe you can ever remove it all, so it could compromise the paint finish in years to come. With the paint off, all we found was a sill section and a rear wheelarch that needed tidying; beyond that, it wasn’t a rusty car.’

Body and chassis specialist Richard lead-loaded the wheelarch repair, ‘Polyester filler can shrink and crack, and it also tends to soak up atmospheric moisture before the paint goes on,’ he says. ‘Lead loading is
authentic – it’s the method used on new car bodies back in the days when the Gullwing was originally built.

 ‘You apply paste-like flux to the steel surface, then heat it with a gas flame to melt the lead content. This gives the lead filler rod [a 95 per cent tin solder much like that used by plumbers] something to stick to when you soften it with the flame. You can then warm it and spread it around with a wooden paddle, before filing it to shape when cool.’

Hours taken: 320

Interior trim

‘The dashboard was an awkward shape, and had to be covered with one piece of leather – that’s how they were done originally,’ says Kevin’s son Rob, who runs O’Rourke Coachtrimmers. ‘It needs to be able to stretch, and some leather stretches more than others. You can use water to make it stretch and hot air to shrink it, but you need to start with the right piece. 

Hides have different properties – choosing the right one is crucial
— Rob O’Rourke

‘Generally, grainy leather stretches more than smooth leather but the area from the belly of the cow has more give in it, so that’s what I used. You can spend as little as £60 on a hide but six months after completion it will stretch and start to look terrible. 

‘The going rate for a hide from a top-quality source is about £350, but you can pay up to £850 if it’s received a special wash or treatment. This car needed five hides in the correct 1060 Cream colour.

‘Fortunately the interior turned out to be highly original and un-messed-with so it went through the workshop quite nicely. Unlike so many cars of this age it hadn’t been repeatedly taken apart and re-made with new holes drilled each time, so we could pay close attention to how everything was done originally and work to those standards. The seats didn’t require anything more than re-covering.

Retrimming the interior involved making correct fitted luggage from scratch using a an original set from a Gullwing as a pattern

Retrimming the interior involved making correct fitted luggage from scratch using a an original set from a Gullwing as a pattern


‘The other unusual job was the fitted luggage, which we made from scratch. We managed to borrow a set of original cases from another Mercedes Gullwing and made paper patterns of all the important profiles from that, then spent many hours researching so we could source the correct rivets, locks and hinges. 

‘For the body of the cases we used thin plywood to make them sturdier than the originals.

‘We found the correct pattern tartan material for the lining in Scotland, appropriately enough, and used the same hide as the seats and dash to cover the exterior.’

Hours taken: 200

Painting was the easy bit. Preparing the Gullwing’s complex body surfaces was far more labour-intensive

Painting was the easy bit. Preparing the Gullwing’s complex body surfaces was far more labour-intensive


Paintwork

We sand by hand using 80-grit, then 180-grit, then 400...
— Mototechnique’s painter James

First we add a skim of filler wherever it’s needed,’ says Mototechnique’s painter James. ‘It’s a micro-layer of fine polyester and is always needed in certain areas – not to fill holes or build up profile, but to achieve a faultlessly smooth surface texture. 

‘Then we sand that by hand, first with 80-grit paper, then 180-grit. Next we apply high-build primer, then sand again, using 180-grit followed by 400-grit. When that’s done, we repeat the high-build primer, and sand with 240, then 400, then 500.’

This laborious process is called blocking, after the rubber blocks used to mount the paper and give the tired painter something to grip. James rolls his eyes when asked how long the whole process of preparation takes, but says it’s far longer for a car like the Gullwing, with its wheelarch ‘eyebrows’ and other unusual contours. 

Filling imperfections using lead solder is an art form – it’s easy to distort the panel with heat, or end up with all the lead on the workshop floor

Filling imperfections using lead solder is an art form – it’s easy to distort the panel with heat, or end up with all the lead on the workshop floor


Finally, after hundreds of hours of preparation, the painting process starts. ‘We use an epoxy primer that acid-etches to the bare metal it comes into contact with and forms a protective moisture barrier in case the paint is ever scratched,’ says James. After this comes a solvent-based primer that’s hand-sanded when dry with 500 grit. It’s now ready for the paint itself. Mototechnique uses PPG’s water-based paint, in this case DB40 Black. 

‘We don’t use two-pack for the same reason you didn’t travel here on a unicycle… there are better ways to do it. There are no solvents to react and evaporate over time, so you don’t get any pinching or dropping in the finish – as you can with two-pack.’

James applied three coats of base coat followed by three of clear lacquer. Unlike the old days of cellulose paint, countless coats and hand-flatting between each one aren’t needed if the preparation is done properly. From here, more arm-aching labour sees the whole car wet-flatted in 1200-grit, then 1500, then 2000. Finally, a machine polisher is allowed near the car to apply one treatment of 3M’s Fastcut and one of Fine. 

Hours taken: 350

Refitting the new and restored parts to the painted body offers a multitude of ways to ding that perfect finish, even when it’s  mummified in bubble wrap

Refitting the new and restored parts to the painted body offers a multitude of ways to ding that perfect finish, even when it’s
mummified in bubble wrap


Engine & running gear

These are big, strong old motors,’ says Mototechnique’s all-purpose mechanic, technician and electrician Colin. ‘But even so, thorough inspection of each component for condition is crucial. You can’t assume that any one item will be okay.’

This is particularly true on a car where the fuel system, transmission and brakes were found to be in such a sub-standard condition. The state of the fuel filter, which was found to be clogged with rusty silt, (see photo bottom right) meant the Mototechnique team feared the Gullwing’s 3.0-litre straight-six would hide some nasty surprises. However, thankfully, the inherently tough overhead-cam design passed most of Colin’s tests so the rebuild process was straightforward.

To check the camshaft lobes he uses a micrometer capable of recording differences as small as one hundredth of a millimetre to see if there is any variation from the original manufacturing tolerances. ‘If the lobe heights are reduced, it can mean the hardened finish is no longer effective, so future wear will occur considerably faster, making replacement a priority,’ says Colin.

When you discover a fuel filter this badly clogged you naturally fear the worst. It’s amazing the car ran at all

When you discover a fuel filter this badly clogged you naturally fear the worst. It’s amazing the car ran at all


You can’t assume that any one item will be okay
— Mototechnique’s all-purpose mechanic, technician and electrician Colin

‘There was no detectable wear on the Gullwing’s camshaft so it could be retained, along with the connecting rods, crankshaft, engine block and cylinder head casting.’ Colin stripped the block bare and gave it a hot caustic clean to remove any deposits that could cause restrictions or blockages in the oilways and coolant passages. 

He decided there was enough wear in the cylinders to demand a rebore, which called for new pistons too. ‘I fitted new valves and unleaded fuel-compatible hardened valve seats, and the crankshaft just needed new shell bearings,’ says Colin. 

Getting it right on the inside isn’t the end of the job. What sets apart a truly top-class restoration can be the detail and effort put into the finish, and the engine bay illustrates this well. The large aluminium casting for the inlet manifold has a smooth and long-lasting finish that’s not quite shiny. It’s achieved by vapour-blasting with small particles suspended in water. 

Straight-six engine comes from the 300 saloon, canted over to fit inside a sports car engine bay and brought to life with mechanical fuel injection. It’s an inherently tough motor

Straight-six engine comes from the 300 saloon, canted over to fit inside a sports car engine bay and brought to life with mechanical fuel injection. It’s an inherently tough motor

Colin then had to deal with the failed fuel injector pump that had kicked off the whole restoration in the first place. ‘We sent this one away to a trusted source,’ he says. ‘They measure and adjust the pump’s metering with a special flowmeter and without this they can never be properly set-up.’

Finally, he moved on to the rear axle. ‘It had survived well,’ says Colin. ‘I just had to replace a few bearings.’

Hours taken: 1136 (all mechanical work)

Correct door fit depends on shims inside the struts. It took days to sort

Correct door fit depends on shims inside the struts. It took days to sort


Fitting

Just getting the doors to fit properly took days and days
— Mototechnique’s body fitter Kevin

‘Those gullwing doors were very time-consuming,’ says Mototechnique’s body fitter Kevin. ‘But you just have to be methodical. Those struts are preloaded, and that preload affects how they shut. They’re made up of one chromed steel tube inside another with a spring inside. The preload is created by shims, so you fit the shims, assemble everything, try the doors, realise which strut needs adjusting which way and try again until it’s right. It took days of fiddling.’

There’s more to it than this, even. Kevin describes how the door rubber’s cross-profile must be exactly right to seal without pushing the door out of the aperture, and how the leather of the interior trim must be seated in such a way that the door rubber can rest over it.

Despite the oceanic patience required to go about each job in the right way, repeatedly, until the result is perfect, Kevin has found things to enjoy about working on the complex Gullwing. 

‘The fit is better than on old Italian cars. Everything is pretty well made and it goes together nicely when you do it all in the right order,’ he says.

The 300 SL was easier to rebuild than a ’50s Ferrari

The 300 SL was easier to rebuild than a ’50s Ferrari

In this sense body fitting is the most important restoration role; after all, Kevin builds the car. And back when the initial stripdown takes place, it’s his job to take exhaustive photos and notes, which are used both as a documentary record of what was done and also a procedural guidebook for the refitting process. This means every connector, every cable and  every wire in the loom must be labelled as they’re disconnected. 

It’s Kevin’s job to assess even the smallest items, and decide on replacement or refurbishment. He had to find stickers for the underbonnet area that use the correct font and wording for the car’s year of manufacture as well as nuts and bolts of the appropriate period size, shape and finish. This approach is sometimes altered to allow treatment to preserve the restoration work. For instance, the cadmium-plated parts receive an invisible coating of wax, sprayed fine to prevent them tarnishing.

The final refit took Kevin 167 hours

The final refit took Kevin 167 hours

But when asked about the biggest challenge he faced with the Gullwing, Kevin doesn’t have to speak. He just frowns a little and gazes at those doors… 

Hours taken: 167 (final refit)

Rear View of restored Jaguar E-type.jpg

Quentin’s view

Never take a car seller’s description at face value
— Quentin Willson
88690611.jpg

There are far too many rubbish repairs and dodgy descriptions in our hobby. Selling a £200k classic that’s not even roadworthy, even at auction, shouldn’t be allowed to happen. I could lecture Tim Jones on the lunacy of buying any classic, never mind a Mercedes Gullwing, unseen under the hammer. But I won’t – because you have to admire the bloke’s unbridled passion. 

The brutal fact of the matter is that very few classics for sale are as good as the seller claims. Unless the car has been maintained by a reputable and meticulous specialist, that ‘original and mint’ motor will, in reality, just be held together by a string of unconnected and sometimes hasty old car repairs. To keep a classic in perfect nick requires enormously specialist knowledge, lots of hours, months of running about and lots of cash. So find who has actually done that alleged resto, what sort of reputation they have and never take a seller’s description at face value. The reason why beautifully restored cars make so much money is that the real deal costs absolute bundles. Anything else is just bodgery and corner cutting. Sad, but true. 

Thanks to: Tim Jones; Mototechnique Ltd (mototechnique.com, 020 8941 3510). Staff surnames were omitted to avoid them being poached by rivals. O’Rourke Coachtrimmers (coachtrimmers.com, 01403 824220)