Tech Q: Magnesium engine block? | FerrariChat

Tech Q: Magnesium engine block?

Discussion in 'General Automotive Discussion' started by BlueBiturbo, Jul 21, 2005.

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  1. BlueBiturbo

    BlueBiturbo F1 Rookie

    May 19, 2004
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    TS
  2. DMC

    DMC Formula 3

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    Difficult to do, but possible. The new BMW N52 inline 6's use magnesium for the upper and lower crankcase.

    http://www.bmwboard.com/news/view.asp?linkid=428

    Unique new magnesium/aluminum composite engine construction
    Recent BMW 4-wheel vehicles (i.e. not motorcycles) have utilized three types of engine construction, all with aluminum cylinder heads:
    • Regular-production 6-cylinder engines (3, 5, Z4, X3 and X5 Series) – aluminum block with cast-iron cylinder liners.
    • V-8 and V-12 engines, new V-10 (5, 7 and X5 Series, M5) – aluminum block with integrally cast silicon-impregnated aluminum cylinder surfaces.
    • M3 6-cylinder engine – cast-iron cylinder block.

    With the N52 engine, BMW introduces a unique and pioneering engine structure: magnesium/aluminum composite construction, the first in a contemporary automobile. Structurally, the all-new engine block consists of three major castings:
    Bedplate (magnesium alloy). This casting forms the lower portion of the block (crankcase), and is similar in concept to a construction element found in some racing engines – as well as the 500-hp V-10 engine powering the new BMW M5.
    Upper crankcase (magnesium alloy). Joining the bedplate at the level of the crankshaft (main) bearings, this too is a weight-saving casting. Mounted onto the bedplate from above; combines with the bedplate to form the cylinder block's outer shell. The result is an ultra-rigid, yet remarkably light engine structure.
    Insert (aluminum alloy). Forms the cylinders and their coolant passages. Analogous to the entire blocks of BMW's V-8, V-10 and V-12 engines, silicon particles are cast into this insert; a "soft honing" machine removes just enough of the aluminum to leave the crystals as ultra-hard cylinder surfaces.

    How it goes together. First, the aluminum insert is cast by conventional methods. Then, during a newly developed die-casting method, the magnesium upper shell shrinks onto the insert while cooling; structural rigidity and stability are ensured by interlocking ribs where the two castings meet.

    In the next step, the upper crankcase, consisting of magnesium shell and aluminum insert, is mounted onto the magnesium bedplate from above. The sintered-steel main bearings' lower halves are in place in the bedplate, the upper halves in the upper crankcase. After the bedplate and upper crankcase have been bolted together, a liquid sealing compound is injected into a groove on the contact surface between the two components. Special aluminum bolts are used to attach parts, such as the engine mounting brackets, to the magnesium/aluminum castings.

    As the "conventional" part of this construction, the cylinder head is of aluminum; however, the head of an inline 6-cylinder engine must be cast with great precision because its length implies relatively large contraction during the cooling-down process after casting. The casting process used here is called "lost-foam"; because all BMW gasoline engines since the 1960s have had aluminum heads, BMW's experience in this regard is long and successful; BMW has used the lost-foam method for cylinder heads since 1997. This process, which employs a polystyrene "dummy" of the head to form the mold into which the aluminum is poured, results in an extremely precise casting of this critical engine component.

    Other weight-saving materials. Though the magnesium/aluminum composite crankcase construction is the most conspicuous example, other materials and production innovations also help pare weight from the N52 engine. One is the adoption of hollow camshafts, which save a remarkable 2.6 lb. Beginning as steel tubes, the camshafts are shaped in a hydroforming procedure, subjected from the inside to a water pressure of 4000 bar (58,000 lb./sq in.) against outer forms to achieve the cam profiles. All this takes place in a cold state – nothing melts – and as a final step the cams are polished to a finish quality of 1/1000 mm.

    The engine's camshaft cover is of weight-saving magnesium. The VANOS sprockets, via which the camshaft chain drives the two variable-valve-timing mechanisms, are newly of aluminum. And the chain camshaft drive – a high-durability, low-maintenance feature of all current BMW engines – has an aluminum chain tensioner that also saves weight. Instead of being a separate casting, the camshaft drive's housing is integrally cast into the magnesium structure, eliminating a production step and sealing components. As one final weight-reducing element, the exhaust headers' flanges are formed from 2-mm-thick steel, significantly lighter than the 12-mm flanges used previously; for a secure seal of this steel to the aluminum head, graphite rings are employed.
     
  3. GrigioGuy

    GrigioGuy Splenda Daddy
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  4. DMC

    DMC Formula 3

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    Argh, how could I have forgotten that?
     
  5. BlueBiturbo

    BlueBiturbo F1 Rookie

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    Thanks for the replies guys. Excellent info.
     
  6. WILLIAM H

    WILLIAM H Three Time F1 World Champ

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    the 1970s Ferrari 512M & the 312PB race cars both had magnesium blocks, they had to be prewarmed before the engine could be started
     
  7. BlueBiturbo

    BlueBiturbo F1 Rookie

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    Thanks Will. I wonder why no other exotic car maker in the 90's uses magnesium block until the new BMW?
     
  8. J-R0d

    J-R0d Rookie

    Jul 5, 2005
    25
    Magnesium burns... So there are some drawbacks to its use.

    For instance, when boring a VW block you have to be somewhat careful. There have been times when chips from the bar ignite, and you don't want the whole block burning (that would be a bad thing).
     
  9. Tspringer

    Tspringer F1 Veteran

    Apr 11, 2002
    6,155
    Porsche 911s used Magnesium engine cases and transmission cases between 1968 and 1973.

    My '69 911S hotrod has a mag case engine and a mag case transmission. Very light...

    The issue with Magnesium isnt really that it burns. It is true that it will burn, but the magnesium alloy used in engine cases and such is extremely difficult to ignite. It takes very high temps to actually get it to burn.

    The problem has always been that magnesium can be too flexible. It is not as stable nor as solid as steel or aluminum. It worked fine for street engines, but Porsche found that under race conditions the engine cases would actually flex causing all sorts of problems.

    On my 911S engine, the engine case was dowel pinned at each crankcase main bearing web to help prevent this. We also used ARP case bolts and head studs to prevent them pulling out of the soft magnesium plus we used case-saver inserts to add strength. We used a 7R case, which was the strongest of the Porsche mag engine cases and had additional webbing. Eventually, Porsche decided the reliability issues were just too big and went back to using aluminum.

    I like the mag cases because between the engine and trans cases it saves about 50lb from the rear of the car.

    Mercedes used Magnesium in racing engines and such back in the mid 1950s. They also bodies some of their racecars in magnesium for lighter weight.

    Porsche experimented with mag for racing chassis. They built a 917 chassis out of magnesium to save weight. The story I read is they kept this knowledge from the drivers who were already freaked out about the cars somewhat flimsey construction and dangerous drivers position (the drivers feet were actually ahead of the front axle line.... nothing but a couple of tiny tubes and some thin fiberglass between the driver and oblivion). The 917 chassis had a tendancy to crack because they were built of such thin walled tubing to save weight. Porsche didnt mind so much, because they built all new chassis for each race (!!). Porsche pressurized the chassis tubing with compressed air and then put a guage on the dash. If the guage dropped to zero, it meant the chassis had cracked somewhere.... The mag chassis didnt work out so well, cracked badly and quickly and they didnt try it again.




    Terry
     
  10. J-R0d

    J-R0d Rookie

    Jul 5, 2005
    25
    Good info.

    It may be hard to ignite in some applications. All I know is that when it was on the boring bar we had one ignite all the shavings, luckily we got it out before it spread any further.

    But, your info makes good sense to me. Thanks for sharing...
     
  11. Horsefly

    Horsefly F1 Veteran

    May 14, 2002
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    If Smokey Yunick had been in charge, he would have used compressed HELIUM instead of air in order to make the car lighter and gain a few MPH.
     
  12. luke9583

    luke9583 Formula 3

    Nov 8, 2003
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    It would be much more impressive to see crystalized Beryllium utilized! :)
     
  13. Kram

    Kram Formula Junior

    Jul 3, 2004
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    Here’s something really exotic: C. Falco has written an article that brings up the perfect material for the head of an engine: Carbon, as in a huge diamond. It would seem that carbon is excellent at transferring heat as well as being rather good in dealing with pressure. Carbon is carbon, but I guess one shouldn’t try this one with molded coal dust.
     

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