Removing mag case corrosion

[Evans, Marv]

I've had my mag case 915 trans stored for awhile. When I went to check on it, it was covered with a bunch of white powder corrosion. Anybody know how to get this off of the case? Chemical wash, brush? What have some of you used? I should have sprayed WD-40 on it when I stored it.
ThanX

[randywebb]

Just get some stuff called Corrosion Block at a marine store - hose it down with that and go over it with a brush. Wait a couple days and wipe off the excess. It'll be fine (or as fine as Mg gets -- just be glad they didn't try to make the case out of Lithium).

[HarryD]

Originally posted by randywebb
Just get some stuff called Corrosion Block at a marine store - hose it down with that and go over it with a brush. Wait a couple days and wipe off the excess. It'll be fine (or as fine as Mg gets -- just be glad they didn't try to make the case out of Lithium).

You know they would have if there was a way!!!

[Grady Clay]

Harry (and Randy),

The critical issue is how to prevent the corrosion in the first place and certainly after “cleaning.”

Porsche originally coated the transmission (and the entire underside of the car) With Valvoline Tectyl 822. I copied the number off the drums at the Factory. It is a solvent based, amber, “one-season undercoat.” In fact it lasts many years if done properly. Porsche was (is) adamant about coating the magnesium parts with this stuff. I have seen unprotected magnesium parts simply disappear from corrosion. I have also seen properly protected ones look like new when re-cleaned. Every time we rebuilt a transmission it was recoated with Tectyl.

Tectyl is available in the States from Daubert Chemical Co. here: http://www.daubertchemical.com/main.taf?erube_fh=daubert&daubert.submit.getproducts=1&daubert.categoryId=1&daubert.productLineId=1
The current product is Tectyl 553.
I think it is distributed worldwide as a Valvoline product.

You cut (dilute) this with standard Stoddard Solvent to the consistency of thin house paint and brush it on. It comes back off with normal cleaning with solvent. I coat all external surfaces except mating surfaces (axle flanges, engine-to-trans surface, starter seating surface, etc.) If you have nice new anodized hardware, it will remain beautiful for years to come.


Another corrosion issue with the magnesium castings is “contact corrosion.” When Porsche changed to the magnesium casting, they also changed to cadmium plating on steel flat washers that contact the magnesium. This prevents electrolytic contact corrosion. You should always use new, well plated washers. I would always additionally dip them in Tectyl for added protection.
With the change from steel spring washers or split lock washers to flat washers, Porsche also changed to nuts with internal locking threads (looks like a Helicoil.)

Best,
Grady

[Jim Richards]

Grady, what is "standard Stoddard Solvent?" Thanks!

[Grady Clay]

Jim,

No, there is no relation to Chuck S. other than I’ll bet he has used a lot of it.

Stoddard solvent (note the lower case – my error) is just basically mineral spirits. It is designed to retain it’s cleaning properties while not being too volatile or harmful to skin and breathing. Needless to say, you should minimize contact with the liquid and vapors. It is what SafetyKleen and other “parts washers” uses. Here is the OSHA data sheet:
http://www.cdc.gov/niosh/npg/npgd0569.html

Stoddard solvent is readily available at home improvement stores and is commercially available in any quantity. It is only slightly less expensive in 100,000 gal quantities.

E-mail me how your project progresses.

Best,
Grady

[Superman]

Ummmm....I do not hunt mice with an elephant gun (though I once shot bunnies with a 30-06 using "kirksite" bullets weighing only 140 grains or so. the bunnies vanished), so I generally reach for something simple in case it works. For many corrosion-cleaning jobs I find vinegar to be very effective. That is the solvent of choice for corroded electrical contacts, anyway (with a final rinse of denatured alcohol). It might work wonders on mag corrosion. I'd try it. Works on your Revere Ware too.

[Jim Richards]

Originally posted by Superman
For many corrosion-cleaning jobs I find vinegar to be very effective. That is the solvent of choice for corroded electrical contacts, anyway (with a final rinse of denatured alcohol). It might work wonders on mag corrosion. I'd try it. Works on your Revere Ware too.

Hmmm, is this an insideous attempt by the SC guys to melt our early mag cases?

Thanks Grady. I haven't heard that name applied to mineral spirits before. Learn something new everyday.

[Grady Clay]

Jim,

I’m not sure mineral spirits and Stoddard solvent are comparable. I only used that term to point out that they are similar.

I think Stoddard solvent is formulated to minimize fire hazard and reduce (not eliminate) adverse effects to human contact. It still maintains great cleaning utility in an automotive environment, ie. it cuts oil and grease very well.

I would never use vinegar on a magnesium case. Vinegar is an acid and will probably increase corrosion. Bad idea for this application.

Alcohol and “lacquer thinner” are probably good to remove the last vestiges of oils prior to coating with Tectyl.

It is reasonable to remove the transmission hardware one-at-a-time and replace the plated flat washer, coated with Tectyl. Then torque back in place. This will help prevent contact corrosion and not loosen the clamping force of all the nuts. Coating the stud threads is also useful.
For maximum protection, I coat with a thin dilute coating, let it dry to very tacky, and then coat with a much thicker less-dilute coating of Tectyl.

Tectyl works equally well protecting aluminum transmission and engine castings.

Best,
Grady

[randywebb]

Vinegar works on batter corrosion because as an acid it reacts with the basic -- uh -- white crud is the best description I guess.

re Tectyl - Thx for that info Grady. There might be something better nowadays.

The Corrosion Block has a good marine following and should work in Oregon's mild and low salt environment.

One can have the trans case powder coated or have another kind of coating put on. I plan to do that when I rebuild mine.

Add this to the yearly or more frequent under car inspection you do....

BTW, Having looked at several of these Mg case transmissions -- they vary greatly in the degree of surface corrosion. Not sure why.

[Reg]

Here is a link to a Mag engine case currently on EBAY that has been redone:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33613&item=7936398272&rd=1

[Grady Clay]

Randy,

I think the reason there is such a variation in condition is that the best ones were never cleaned and are still covered with oil and grunge. The Magnesium transmissions that were reinstalled perfectly clean and no protective coating were subject to the most corrosion.

I don’t think “powder coat” is a viable solution either. It is subject to cracking (particularly at the fasteners) and the corrosion will propagate under the paint.

I don’t think I can stress enough the importance of this protective coating for mag parts.

Best,
Grady

[Oldporsche]

There are probably several "versions" of mineral spirits. In general I call around to the petroleum distributors locally when I'm looking for a parts cleaning solvent to put in the parts washer. At the local distributors I call for Stoddard solvent, at Wal-Mart I call for paint thinner. Very often Wal-Mart price per gal beats the distributors.

Good luck,
David Duffield

[thomschoon]

Originally posted by randywebb


One can have the trans case powder coated or have another kind of coating put on. I plan to do that when I rebuild mine.

I would not powder coat the case, while working for a rather large aerospace company in Seattle I had a project that implemented powder coat for mag steering wheels, they were all "DOW 17" coated and we could only powder coat a couple of times as the mag doesnt like the heat all that well and would degrade as well as distort. Powder coat can also hide corrosion so copy what the factory used and play it safe.

Just my $.02 minus taxes

[randywebb]

That's interesting - thanks, folks. You all know about Grant G's car? It's the "Carbon Copy" lightwt. that was in an Excellence article. As I recall, his trans. is black. Dunno if it is MG case or Al case. I've seen some other black trans. in photos. Are they doing it wrong? Or what are they doing?

There are other coating technologies around (note my comment "or have another kind of coating put on" - that's what I was thinking of). I don't know of one esp. designed for Mg tho. Do you know of something for Mg?

Oil & grease, etc. will remove the Tectyl pretty rapidly I think.

[thomschoon]

The Tagnite process is pretty tough it seals the magnesium so corrosion can not start and is tough as heck. It is used in several aerospace applications including helicopter gearboxes. Here is the link:
http://www.tagnite.com

[Tom F2]

Interesting thread. Here's what I know about treating magnesium castings. Never use chemical gasket removers on magnesium. The methyl chloride in them corrodes magnesium.

[Zeke]

I made a tranny brilliant with muriatic acid. I had to work swift ly and carefully as the acid would eat the metal rapidly. I couldn't get much, if any, on the mating surfaces. but, it was as bright as new aluminum.

I'm just saying this to suppor the vinegar idea. The acid is too strong and an environmental problem. Local environment, anyway, you just want to not be around strong acid. I diluted with lots of water, like the hose.

I did some research on acid cleaning. Phosphoric acid cleans AL marvelously, but, again, same handling problems.

Maybe there are acid cleaning facilities with a controled process. Again, my concern would be with the mating surfaces. I destroyed one intermediate plate doing this.

[Evans, Marv]

Well, I went to a marine supply store like Randy suggested and bought a spray can of Marine Block (12 oz. for $18). I'm going to try that first. I'll let everybody know what my experience was, but the way I work and with the time I have, it may be awhile. The thing is, I also have two engines stored. Both of them have this corrostion too. So, eventually I'll have to do them. I think I'll try to get some Tectyl to coat them with afterwards. The funny thing is, I had these all stored in a garage for a long time without any corrosion forming on them. After I sold the property where I had them stored in the garage, I transferred them to one of those steel storage containers I rented at a storage place. It was only after being stored in the container they started getting corroded.

[Grady Clay]

Randy is correct, oil & grease will remove the Tectyl. Usually that isn’t a problem because the oil & grease will protect the casting.

The common ingredient in this kind of corrosion is WATER. It can be in gas form (humidity) or in liquid form (aerosol fog or condensation.)

Another issue is; are we talking about a bare casting with no studs, bearing races, etc. or an assembled transmission with all the steel parts in place?

I am concerned about the contact (electrolytic) corrosion where the acid gets to the edge of the steel washer where it contacts the alloy. The same issue is for the acid getting between steel threads and the threaded alloy casting.

I agree with Milt, you can make an absolutely beautiful cleaning job. I’m talking about having the castings last another decade and more without dissolving into a fine white powder.

Best,
Grady