Exploding Wheels Revisited

I have read the posts concerning Cornpanzers American Racing magnesium wheels and the concensus seems to be their structural integrity is questionable due to age and internal corrosion :eek: Yet in the same vein I have seen/heard nothing pro or con concerning the Mahle 5 lug magnesium gasburners which Porsche offered on the 1970-71 911 T and 914-6 :confused: I realize the ratio/type of alloying metal used in the casting process can affect the strength plus finish coating to a degree but it seems doubtful that an external finish is going to curtail internal corrosion in my opinion. I'm sure the collective knowledge of this board will shed light on this AR taboo/Mahle acceptable paradox.
Mark
Early S Registry #351
Rgruppe # 247

I can't comment on why or if Mag wheels made on either side of the Alantic may be better than the the other. Did Mahle have superior material and casting techniques to AR? Is the primer sealer on Mahles superior to the AR sealer?

The mag rim I saw fail was in a racing accident. Unlike a forged aluminum rim that hopefully will bend or crack the mag wheel I saw failed into a couple dozen small brittle chips the size and shape of clip on wheel weights.

I don't know. But here is a little info on mag wheels in general that may apply to all mag rims. I googled your question and found this site http://www.roadsters.com/wheels/.

Magnesium is beautiful. If brightly polished aluminum resembles chrome plating, polished magnesium is more like nickel plating, with just a hint of gold to it. No other metal looks like it. Magnesium that has been brightly polished is unique and striking.

Magnesium is strange stuff. After you polish it to a beautiful mirror finish, as time passes it will gradually turn gray, and then dark gray, with a bit of green.

Magnesium is extremely difficult to weld. Generally speaking, the more someone knows about welding, the less likely they are to want to have anything to do with repairing magnesium castings.

Magnesium is dangerous. If it ever catches fire, throw a bucket of sand on it and run for your life. When magnesium burns, it virtually can't be stopped. Small quantities of magnesium are used to make photoflash bulbs. Larger quantities are used to make bombs.

Magnesium is exotic. In the world of vintage race car parts, there is no other metal that is so tough to deal with. But many of the most desirable drag racing parts were made out of magnesium, including blower housings, end plates, manifolds, and pulleys, fuel filters, fuel injectors, late Hemi timing covers, oil pans and valve covers, Ford and Olds differentials, quick-change rear end center sections and covers, and some really neat wheels.

Magnesium is a pain. But its use plays an important role in hot rodding, and we deal with it.

The biggest challenge in taking care of magnesium parts is preserving them. With exposure to humidity, magnesium oxidizes, and tiny craters that are commonly called pits are formed. When magnesium parts are left unprotected and exposed to moisture, these pits eventually can grow to over an eighth of an inch in diameter.

I've seen a pair of magnesium racing wheels that were left lying outside in a field for many years. They had craters as big as three-eighths of an inch across all over them.

The twelve-spoke wheel on the left is on an old Willys Altered that has sat outside for several decades.

This stuff is alive.

A sign that magnesium castings are getting ready to become pitted is the appearance of a fine white powder in places. While very minor pitting can be removed with emery cloth, the best thing to do is to make sure it doesn't happen in the first place.

Most magnesium wheels were produced by sand casting. You should expect to find some imperfections in the castings. As far as telling whether you're looking at pitting or casting flaws, that's a tough call without seeing them. It's a safe bet that they have a number of relatively minor casting flaws, and it's inevitable that they've got some pitting on parts of them unless they've been stored in an airtight drum filled with oil.

If you're shopping for vintage magnesium parts with the goal of building something that's show-quality, you have to start with something decent. Unless the parts you looking for are extremely obscure, there's enough of this stuff out there that you don't have to settle for parts that are badly pitted.

Magnesium parts must be stored in a dry area that is free of humidity. Bare magnesium wheels can be sprayed with WD40, which will offer some protection until it evaporates. Some people store their magnesium parts in thick plastic bags, and use a vacuum cleaner to draw as much of the air out of the bag as possible before tightly sealing them.

I've experimented with some ideas to keep my magnesium Americans and Halibrands shiny. WD40 did okay, but it leaves metal parts sticky and makes dust hard to remove. The one product that amazed me was Gibbs Brand, which is advertised as being a "mega penetrant". After spraying Gibbs Brand all over my satin-finished magnesium Halibrands (and aluminum Torq-Thrusts), it has proven to work amazingly well. You can learn more about it on this site's page about Gibbs Brand.

The stuff is alive.

FWIW, I had heard about the war stories... if there was a magnesium fire (flares ?) wound, other guys/soldiers would extinguish the fire by dumping dirt/sand on his wound/fire to remove the oxygen. When the MASH doc (?)/medic would remove the dirt/sand, the magnesium fire would re-ignite because oxygen was available again. Maybe someone could experiment with a road flare?? How could it keep the heat necessary to automatically re-ignite? Mythbusters, anyone?
I have some Mahle stoveburners but they still have the factory paint. When mag Halibrands or Americans were new, they had a gold anodizing (Dow7)to protect the magnesium from moisture (humidity)/acid (dogs). To get a nice polish, everyone had the anodizing/Dow7 removed, so the mag became vunerable to corrosion.

Maybe if someone has some fully polished Mahle stoveburners that have been left out for a while or exposed to salt/snow/humidity they can check for external corrosion or pitting...

Mark, you have a PM.

The Mahle's had the advantage of being pressure cast which from my understanding creates a less porus finished product (less prone to absorb moisture), plus they were coated inside and out from the factory. They seem to hold up much better than the vintage cast wheels like Americans and Halibrands.

FWIW, many vintage racers (drag and sports) still race on old mag wheels. All those wheels you see on 917's, 908's, Cobras, GT40's etc etc are magnesium and in many cases nearly 40 years old. I feel the risk is very low (and apparently so do they), but even on my own car I choose to use my Fuchs if I am involved in any sort of "competitive or spirited driving". No need to take any additional risks.....even if they are minute.

I dont feel that one persons outspoken opinions make something "Taboo" anyway..... :rolleyes: :)

Mike, great site! That guy has expanded it a lot since the last time I was there - full of quality info! One thing I noticed, was that when you were quoting his text your own personal comments got inter-mixed with the quote. Thought it may be confusing to others. You have mentioned the wheel that you saw "fail" before in another post. I find it odd that you keep forgetting to mention the small detail that the vehicle in question barrel-rolled at 100 mph after slamming into a wall. (not precipitated by a wheel failure) Oddly enough, the roof, doors, fenders and many other parts "failed" at the same time as the wheels :rolleyes:

FWIW, I had seen a NOS Halibrand with its original box... it had DOW7 gold coating inside and out... (at least that's what I remember... I don't remember seeing any exposed/uncoated magnesium).

Quote:

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Originally Posted by Cornpanzer

You have mentioned the wheel that you saw "fail" before in another post. I find it odd that you keep forgetting to mention the small detail that the vehicle in question barrel-rolled at 100 mph after slamming into a wall. (not precipitated by a wheel failure) Oddly enough, the roof, doors, fenders and many other parts "failed" at the same time as the wheels :rolleyes:

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Your position that Mahles are pressure cast and everyone else races with antique mag wheels of different origins has not swayed my humble opinion.

Why not offer that risks with these wheels can be reduced if they are frequently crack checked prior to use of any type. Perhaps the guys vintage racing expensive cars take this precaution. Also be prepared to run tubes if you get stuck with a leaky mag wheel, ask Paul about his ride back from the last North meets South.
He fixed the problem be finding a set of forged aluminum replicas to replace a leaking centerlock mag rim.

Your quote above misses my point entirely. The accident in question happened to me in Ca (you where in Ohio at the time?) while a friend and I were drag racing our cars at the Sacramento drag strip. The other car crashed at 100mph right in front of me, I narrowly avoided him. His car tumbled hit the rail I saw it all in my rear view mirror. Point taken any wheel would fail from this abuse. My point is how the wheel failed.
I have seen many forged aluminum rims crack and distort. This mag rim was unique. They don't bend; they crack into small brittle shards. If I am racing I hope my wheels bend and give before they splinter into clip on wheel weight size shards.
Get off the computer and get yours crack checked. :D

Porsche is using Mg wheels on the C-GT. I read in a race car materials book recently that it's been discovered that the reason Mg was so crack and corrosion prone in the past was impurities in the alloys used, and that has been greatly reduced recently.

No idea if that is what is going on with the C-GT wheels, or what alloy or protective coating Porsche is using on them. But it's a thought for some one to make a run of light weight, vintage sized and vintage look wheels for our 911s.

-- not that ceramic rotors wouldn't be a better idea, tho.

Quote:

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Originally Posted by Gburner

Your position that Mahles are pressure cast and everyone else races with antique mag wheels of different origins has not swayed my humble opinion.

Why not offer that risks with these wheels can be reduced if they are frequently crack checked prior to use of any type. Perhaps the guys vintage racing expensive cars take this precaution. Also be prepared to run tubes if you get stuck with a leaky mag wheel, ask Paul about his ride back from the last North meets South.
Get off the computer and get yours crack checked. :D

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Whatever dude. My posistion has always been the same - it hasnt changed. There is nothing wrong with running mag wheels on the street. Chances are, there is not much risk running them on the track either....but like you I feel discretion is the better part of valor.

Yes, I was in Ohio when the above mentioned incident happened. Contrary to what you are trying to imply, I do have some knowledge....secondhand as it may be since you phoned me hours after the incident and described it in detail. Back then you had no problem with racing or driving on mag wheels. In fact, shortly after that incident you began racing on mag wheels yourself - no problem with them then either . I know this, because I sold them to you.

I agree 100% that it is the course of wisdom to have old magnesium wheels crack checked before use. Duh! My beef is that your vendetta against magnesium wheels ironically coincided with your personal issues with me. Get on with your life.