Wheel Recall ( Snowflake ) - The Definitive Truth

[0m3nc0w]

Nope, just need to slowly heat to the temperature for the specific powder and slowly cool. Changing the metallurgy only occurs with rapid changes.

The OEM gold snowflakes are factory powder coated to be gold.

[Ken in Oklahoma]

Nope, just need to slowly heat to the temperature for the specific powder and slowly cool. Changing the metallurgy only occurs with rapid changes. . .

Hmm, that flies in the face of my understanding. If we were talking about high carbon steel that would be true. To harden high carbon steel it is the rapid cooling (quenching) from roughly cherry red hot to, say, room temperature that locks the carbon atoms into a lattice with the iron atoms. The resultant lattice is brittle but strong.

If cooled slowly the carbon atoms will find each other and nodules of carbon will form in the steel, and the result will be soft iron which has embedded carbon nodules in it. The iron is very 'bendable', or soft if you prefer.

But that's (high) carbon steel. Other metals, such as copper, or aluminum, or brass (which is an amalgam of copper and zinc) do not act that way. The other metals such can be work hardened (such as the copper wire in house wiring) or alloyed with other metals in order to attain a harder, stronger, metal.

Please pardon me if I sound preachy. That's not my intention.

The core question here is whether a snowflake wheel will be softened in the powder coating process. I simply don't know. Until I did know I would be loathe to subject a snowflake wheel to the higher temperatures associated with powder coating. I would be particularly concerned about the fit of the bearing races into the wheel.

Aside from all of that, carbon steel can be fun to 'play' with. Hacksaw blades come in many flavors (alloys), but the cheaper ones are likely to be a more simple high carbon steel. Take a worn out hacksaw blade, heat it to a glowing red with a propane or acetylene torch, and then quench it quickly in water. Then, holding the hacksaw blade in a pair of vice grips smack the quenched end against a vise and see the end of the blade shatter. Like glass!

I have a set of (some brand name) dividers that wouldn't make layout (scratch) marks on steel. They were wonderful name brand dividers, acquired at some flea market, but not terribly useful to me. With little to loose I decided to heat and quench the divider tips. That was easy enough to do with a propane torch and a glass of water. I did no tempering of the points, choosing to leave them as hard as they could be. I was, of course, risking dropping the dividers onto some concrete and breaking a tip. Using a fine grit grinding wheel and finishing with some diamond whetstones I created some nice sharp points. And I was very gratified to see the points of the dividers generate some nice scratch marks on a bit of mild steel.

Another fun with metals thing I did was to salvage some old copper house wiring. The wire was quit stiff, the natural result of work hardening as the copper wire is drawn thorough successively smaller dies. I decided that I could use some soft copper wire so I decided to anneal it. I stripped off the insulation (not all that easy) and heated the wire to a glowing red hot and then let it cool. I now had an ugly blackened piece of copper wire with all kinds of bends in it. I clamped one end of the wire into a bench vice and grabbed the other end with a pair of vice grips. I then 'snapped' the wire by bringing my arm down quickly, giving the wire a big yank. The result was a nice straight length of ugly blackened copper wire. A bit of steel wool scrubbed enough of the black away to suite me. So I now have some nice straight copper house wire which I may some day find a use for.

And that's all I have to say about that.'

Ken

[0m3nc0w]

I don't have a degree in metallurgy however I understand your concerns, and it would be no bueno to weaken the castings and have the wheel break apart when riding.

However making the rims more brittle is not at issue since they are being cooled very slowly, the only possibility for changes is annealing by exceeding the annealing temperature. Different temp ranges exist for different alloys and different types of annealing processes. The general range for the typical (as any that would be used for a motorcycle wheel) aluminum alloys is 250F to 985F. Also, bear in mind that the material generally needs to be held at those elevated temps for sustained periods of time for the annealing process to take place, much longer than would occur with powder coating processes (30 minutes).

However, it should be understood regardless, that annealing does NOT weaken aluminum alloys -- rather it actually INCREASES temper. That is precisely why it is done. Therefore, even if the powder coat process reached the range of annealing temps, it would not have any adverse effect on the alloy's strength, in fact, it could possibly improve it. The only caveat here is that care should be taken to ensure that the material (wheel) is allowed to cool gradually on its own (by air only at room temp) and not accelerated, as cooling too quickly could cause potential problems with hardening (becoming brittle).

It should also be understood that there are so many different types of aluminum that no one can say anything specifically about the dangers of heat treating an aluminum part unless they know the exact components of the alloy. For example see a current breakdown of the types of aluminum alloys available for casting:

http://www.mid-atlanticcasting.com/alum ... _FEB05.pdf

It's pretty complicated stuff, furthermore these change every year or so - so one would need to contact BMW and ask what type of aluminum was sourced for the wheels that year and then find the data sheet for that type of aluminum back when it was fabricated. Probably not easy.

Bottom line is the front wheel is powder coated by the factory so I'm not outside of my comfort zone by changing the color and having them baked again.

[khittner1]

Bottom line is the front wheel is powder coated by the factory so I'm not outside of my comfort zone by changing the color and having them baked again.

I always thought that the silver snowflakes were painted. Are the gold ones different in this respect?

[0m3nc0w]

The silver ones are raw aluminum, the gold ones are powder coated.

[Texer]

"A bit of steel wool scrubbed enough of the black away to suite me. So I now have some nice straight copper house wire which I may some day find a use for."

The description of snapping that wire straight just for satisfaction is the good stuff that I often come here for.

[SteveD]

The silver ones are raw aluminum, the gold ones are powder coated.

I've seen a replacement silver one that was painted, certainly not the same surface as the originals.

[barryh]

My 79 snowflakes are painted and I'm almost certain that was the original finish as they came to me wearing the original factory tires.

[jagarra]

When I had items powder coated and I had to use a filler to repair surface imperfections of the metal, I was told that the filler had to be able to stand a temperature of 400 degrees. If I remember correctly, when I used JB weld, it ran.

[0m3nc0w]

My 79 snowflakes are painted and I'm almost certain that was the original finish as they came to me wearing the original factory tires.

The 1978 rear Snowflake drum brake wheel is different from every other year. In fact it is referred to as "odd-ball orphan", meaning '78 was the only year they were made like this. There is an aluminum cap with 5 allen bolts on the left covering the seal retainer and has a NON-STEEL insert hub that must be heated for bearing service. This is a poor design and BMW gave up on it immediately.

Now I'm not sure if that has anything to do with whether or not they were painted silver other years and not in '78, but I am certain they don't have paint on them as I took a wire wheel (on a Dremel) to the front wheel where the spokes meet the hub in an attempt to search for small fractures before I started the whole recall process. There was definitely no paint on the metal. Also the rear wheel has some pretty significant scratches (gouges really) where someone tried to strong arm a tire change. It's evident that there is no paint on the rear wheel either.