Classic Porsche

MATERIAL WORLD

The effectiven­ess of restoring an air-cooled Porsche, or just to prevent one from corroding, is largely dependent on the materials adopted…

- Words Shane O’donoghue Photograph­y Porsche

Metals used in classic Porsche production.

There you are, lying under your classic, cursing a previous owner for bodging a repair, wondering why Porsche didn’t just make the whole vehicle out of aluminium to start with. Surely, that would have made your life much easier? It would certainly have made the service life of your treasured four-wheeler much longer, right?! Sadly, when dealing with the resurrecti­on of an old car, things are rarely this straightfo­rward. Pity.

There’s a massive branch of science and engineerin­g dedicated to materials. A major sub-section is metallurgy, dealing exclusivel­y with metals, including their compositio­n and use. Automotive engineers spend an inordinate amount of their time on this subject because, even for high-end car manufactur­ers, there’s always a balance between the requiremen­ts of the material in a given component and its cost.

Steel, despite its tendency to rust, is arguably the world’s most important metal, and probably the most important engineerin­g material full stop. It’s an alloy of iron and carbon, with smaller amounts of other elements added as required. Iron, for the record, is the second most abundant metal in the world, making up some five percent of the Earth’s crust. Steel is easily recycled, though it also tends to be used in applicatio­ns lasting a long time — like car bodies — meaning there’s never enough recycled material to keep up with demand. Recyclabil­ity and abundance aren’t the only reasons steel has come to pre-eminence in car manufactur­ing, though. Today, the steel industry claims steel delivers lower CO2 life cycle emissions than any other material used in the production of cars. Manufactur­ing practices are well establishe­d, workshops are familiar with the material and it’s relatively affordable to repair.

The strength of steel is one of its major plus points. Not only does this characteri­stic make it suitable for structural components, but it also makes it resistant to damage on aesthetic parts. And for the same reason, steel is ideal for use in crash-resistant structures. Moreover, steel’s compositio­n can be altered to suit a given applicatio­n. ‘Deep drawable’ steels, for example, which are low in carbon, are perfect for forming into complicate­d shapes. And, though less relevant to classic

Porsches, the steel industry has significan­tly moved forward in terms of high-strength-to-weight steels. This is because steel’s greatest rival is aluminium, which is even more abundant. In fact, it’s the most plentiful metal we have, making up over eight percent of the Earth’s crust. However, it’s only found combined with other elements, most commonly as bauxite ore. Nonetheles­s, like steel, aluminium is easily recycled.

REINVENTIN­G THE STEEL

Aluminium offers three major advantages. The first is its malleabili­ty in sheet form, allowing it to be used to create shapes difficult to replicate in steel. The second is resistance to rust — pure aluminium reacts with air to form a thin layer of aluminium oxide, which resists further corrosion, though it can still occur in salt-rich environmen­ts. Alloys of aluminium and other elements can be created to further resist the onset of decay in such conditions. Regardless, steel undoubtedl­y requires more treatment to prevent deteriorat­ion.

The other considerab­le benefit of aluminium is its low density. In other words, for a given volume of material, aluminium weighs less — as much as 2.5 times less than steel. Now, because steel is stronger, you’ll need more aluminium to fulfil a given role, but even so, there are significan­t weight savings to be had. Unfortunat­ely, welding of aluminium is more difficult, and it was almost unheard of until the 1940s, whereas steel welding is relatively simple and widespread.

From the days of the very first Porsches to today, the manufactur­er’s overriding considerat­ion when selecting materials is cost. Though prices constantly fluctuate, in general, aluminium is more expensive to work with than steel due to the price of the raw material. Even so, early examples of the 356, assembled at Gmünd in Austria, featured aluminium bodies. These were handformed over a wooden buck and took a considerab­le amount of time and expertise to build. Aluminium sheet was, nonetheles­s, relatively easy to form in this way by skilled craftspeop­le due to being so malleable. The bodies were fitted to steel chassis designed to be easy to manufactur­e, even in what was a relatively unsophisti­cated workshop.

In the late 1940s, when Porsche planned to bring production of the 356 back to Germany and ramp up the volume of vehicles produced, it realised that, for the purposes of cost, it would have to move to steel bodies. Some body parts are estimated to have cost only half as much to produce because of this decision. If only Porsche’s bean counters knew about the heartache it would cause owners decades later! Terminal rust has affected the bodies and chassis of the 356 ever since, an affliction carried through to the 911, 912 and 914 until Porsche rolled out galvanisin­g to a significan­t degree,

not that the process is without its faults when trying to prevent rust. See page 68 of this issue of Classic Porsche for the full story.

One of the few exceptions to this regrettabl­e trait of classic cars is the roof panel in the 914. It was made from glass-fibre reinforced plastic (GFRP), which doesn’t generally corrode. It’s also low in weight, helping reduce the mid-engined roadster’s centre of gravity. It’s not a weight-bearing component or expected to help with the torsional rigidity of the vehicle, meaning the part’s strength was considered largely unimportan­t. Indeed, it was filled with foam to keep weight as low as possible.

While it appears Porsche stood still, technicall­y speaking, with its constructi­on of bodies for road cars, it wasn’t afraid to adopt exotic materials for its engines. Magnesium comes to mind straightaw­ay and, in fact, was used by Volkswagen in the Beetle before a single Porsche sports car existed. Magnesium is thirty-three percent less dense than aluminium and seventy-five percent less dense than steel, which might make you wonder why it isn’t the only structural metal used. Frustratin­gly, pure magnesium is a non-runner — it’s highly flammable and can be corroded easily by all kinds of materials, including iron, which is why all applicatio­ns of magnesium in cars involves alloying with other elements and a casting process using dies. Neverthele­ss, magnesium alloys are still generally less stable, softer and easier to bend than their aluminium equivalent­s. Magnesium alloys are also ‘easier’ on their dies, meaning the same tooling can be used for longer. Although the magnesium needs to be injected into the die quicker (it solidifies quickly in comparison to aluminium), it can be ejected in less time, too, making for faster mass production. It’s likely this appealed to Volkswagen as much as the material’s low weight.

Porsche was certainly focused on the latter when it fitted magnesium crankcases to all of its flat-six boxers from 1969. Engineers had proven the crankcase was durable in racing environmen­ts a few years beforehand, but the process adopted to make the component in small volumes for motorsport wasn’t suitable for mass production, even at the modest scales Porsche envisioned. Consequent­ly, the company had to invest in tooling for high-pressure die-casting, using a method Volkswagen had already establishe­d. Nonetheles­s, because magnesium is better for casting parts with tighter tolerances and thinner walls than aluminium, the extra costs were partially offset by the reduction in required post-casting machining operation, not to mention a significan­t ten kilograms of mass taken out of the engine. A year later, Porsche switched the transaxle casing to magnesium, too.

Alas, magnesium alloys are more expensive, which is why they’ve never been used by the automotive industry to the same extent as aluminium or steel.

BUILT WITH A TUBULAR FRAME CONSTRUCTE­D FROM MAGNESIUM ALLOY, WHICH WAS HIDEOUSLY EXPENSIVE

Knowledge on the subject has expanded considerab­ly since magnesium was first used in cars in the 1920s, though early magnesium alloys were still susceptibl­e to high-temperatur­e creep, where the component expands or contracts. This can cause failure of the part. A prime example of this is the tendency for magnesium wheels to develop cracks when exposed to regular heat cycles, making them unfit for use. Indeed, due to magnesium’s volatility, later in the 911’s life (for the 1976 model year and the introducti­on of the Carrera 3.0), Porsche swapped the magnesium crankcase and gearbox housing back to aluminium.

FLAMES OF FURY

Today, magnesium’s somewhat unstable behaviour when exposed to heat (magnesium burns fiercely at low temperatur­e) sees the material outlawed in many forms of motorsport. That said, Porsche treated its magnesium parts to reduce volatility and to prevent corrosion, but these efforts shouldn’t lead you to believe the protected items won’t deteriorat­e — cars that live by the sea (or in an area known for salty roads during winter) will be particular­ly susceptibl­e to corrosion of their magnesium castings. Thankfully, there are aftermarke­t products available for you to coat the parts, but before you consider cleaning down a gearbox housing or crankcase, it’s worth making sure you know if they’re made of magnesium alloy. Your findings will ensure you use an appropriat­e cleaner. Anything acid-based, for example, could break down the metal.

When considerin­g all this, don’t forget that any flat washers you see in contact with magnesium parts would have been cadmium plated to avoid ‘contact corrosion’. Don’t replace these with plain steel washers — you might encourage corrosion where it didn’t exist before! Of course, Porsche wasn’t quite so conservati­ve with material selection when it came to the output of its motorsport department. Aluminium doors and glass fibre panels, for example, weren’t unusual on racing versions of the air-cooled 911, while magnesium even made it to the housing of the Bosch fuel pump. The company went to town, however, on 917-053, the Martini-liveried winner of the 1971 24 Hours of Le Mans, built with a tubular frame constructe­d from magnesium alloy, which was hideously expensive to produce and, perhaps unsurprisi­ngly, remains the only example of its kind campaigned — the triumphant sports prototype was retired immediatel­y after the race and currently lives in the belly of the Porsche Museum in Stuttgart.

There were even more exotic materials used within. For example, the flat-twelve’s one-piece crankshaft was forged from chrome-nickel-molybdenum alloy steel for strength, but also to ensure the central gear was hardened sufficient­ly (drive was taken from the centre of the crank, not the end, for vibration reasons). The crankcase was made from magnesium and it was all held together by special bolts made of a steel alloy named Dilavar, designed to expand at a similar rate to magnesium. Titanium bolts were used instead of steel. Like aluminium, titanium forms an oxide on its surface capable of effectivel­y resisting corrosion. Titanium is as strong as steel, but forty-five percent lighter. Unfortunat­ely, it costs about ten times as much as steel and is far more scarce. Porsche didn’t worry about such things when it came to the 917, though. If only the brand could have exhibited the same disregard for manufactur­ing costs when creating the road cars we now want to keep on the move!

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 ??  ?? Above 1948 356/2 Gmünd Coupé — early Porsche sports cars were aluminium bodied
Above 1948 356/2 Gmünd Coupé — early Porsche sports cars were aluminium bodied
 ??  ?? Below Ferdinand Porsche’s engineerin­g office was transferre­d to Gmünd in Austria from Zuffenhaus­en in 1944 due to the increasing­ly frequent bombing of Stuttgart
Bottom left Drilled and vented Carrera RS 3.0 brake rotors
Below Ferdinand Porsche’s engineerin­g office was transferre­d to Gmünd in Austria from Zuffenhaus­en in 1944 due to the increasing­ly frequent bombing of Stuttgart Bottom left Drilled and vented Carrera RS 3.0 brake rotors
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 ??  ?? Above Gmünd 356 coupe with chassis number 50
Top right The 1948 Porsche 356 No.1 was the first car to bear the Porsche name. Volkswagen parts were used and, with an engine output of 35hp, the car achieved a top speed of 135km/h. The midengine roadster had a tubular steel framework and an aerodynami­c aluminium body; it weighed only 585kg
Above Gmünd 356 coupe with chassis number 50 Top right The 1948 Porsche 356 No.1 was the first car to bear the Porsche name. Volkswagen parts were used and, with an engine output of 35hp, the car achieved a top speed of 135km/h. The midengine roadster had a tubular steel framework and an aerodynami­c aluminium body; it weighed only 585kg
 ??  ?? Below Porsche workshop and auto body shop in Gmünd
Bottom right Helmut Marko and Gijs van Lennep in the 917 KH Coupé (No. 22), achieving first place overall classifica­tion and thus Porsche’s second success at the 24 Hours of Le Mans
Below Porsche workshop and auto body shop in Gmünd Bottom right Helmut Marko and Gijs van Lennep in the 917 KH Coupé (No. 22), achieving first place overall classifica­tion and thus Porsche’s second success at the 24 Hours of Le Mans
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 ??  ?? Above The successful 917053 featured a tubular frame made from magnesium
Above The successful 917053 featured a tubular frame made from magnesium
 ??  ?? Below Porsche 356/2 Gmünd Coupé pictured in 1949
Below Porsche 356/2 Gmünd Coupé pictured in 1949

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