Magnesium Corrosion

Ant · #1 (**permalink**) 07-14-2006, 04:13 AM

I have a Magnesium case five speed Jerico transmission in my Cobra, problem is minor but the magnesium case gets grey fluffy corrosion over it, been a wet winter here and the moisture content is up in my dry garage!
One thing I have done is put a light film of oil over the outside of the trans, and the internals have a bath of synthetic Castrol gear oil. Also I thought about using the yellow/green aircraft paint commonly used in the build of aircraft, or I could just leave it to go grey or black!

How do I slow down this corrosion, interested in hearing from anyone who has dealt with this material?

Woodz428 · #2 (**permalink**) 07-14-2006, 04:57 AM

I'm not sure about the metallurgy content of those cases, but I would at least paint it with SOMETHING to seal it up. The aircraft paint you mention sounds like a good idea.In case you are unaware,one of the reasons magnesium was dispensed with in wheels is because of their fondness to ignite when a tire would blow out and they would drag on the roadway/track. They do also want to return to their original form. It use to be that magnesium was 'farmed" from the oceans, but there may be other ways now.

Ant · #3 (**permalink**) 07-14-2006, 05:23 AM

Woodz428,

I would have been quite happy if my trans was made out of aluminium and not this stuff I have, but the corrosion is very minor and no pitts or anything at this stage.
You are right it needs protecting, I have read where the grey/white surface corrosion can protect it a bit, but have since found on the web a product called "Gibbs Brand" this product has many uses including firearms etc and stop the corrosion for years, the magnesium may still go black but have a shiny surface, I suppose that is similar to metal anti rust preparations that form a potassium based oxidation surface!

I dont know what they have here in NZ, but I guess I can get a couple of cans of a suitable product shipped out, or a suitable spray gun oil like G96 may do it, but they wont air freight aerosol cans.

double ugly · #4 (**permalink**) 07-14-2006, 10:30 AM

In the old days we used WD40. It kept a Hewland from oxydizing. Paint would work but if we needed to crack check the gearbox we would have to bead blast the paint off. You could apply the WD40 while tranny is in the car. I hope this helps some.
John

CobraV8 · #5 (**permalink**) 07-14-2006, 10:53 AM

On VW Bugs they used a magnesium transmission case in the 50s. However after Volkswagen solved an engine oil leak problem as part of a production change they ran into problems with the corrosion that occured due to the lack of oil mist sprayed over the tranny

At least that's the story I have been told...

I would just spray the case with WD40 from time to time as double ugly recommended.

Simon

Sizzler · #6 (**permalink**) 07-14-2006, 11:16 AM

what exactly is wrong with the oxidation?

usually oxidation acts as a shield for the underlying metal, once formed. Why do you want your transmission all shiny?

maybe mag oxidation doesn't protect the underlying metal?

How are the old unpainted mag wheels from the 60's holding up?

personally, I'd prefer the look of oxidized mag to an oily case.

Tinker51 · #7 (**permalink**) 07-14-2006, 11:22 AM

What you're after is this http://www.aircraftspruce.com/catalo...agtreatkit.php
The conversion coating will clean the mag up and prep it for paint.
The paint you are referring to is zinc chromate.http://www.aircraftspruce.com/catalog/cspages/zinc.php
The green is the color shown on the can in the picture. The yellow is about the color of avocado meat.
The warning about zinc chromate and lung cancer is not kidding. Best to paint the tranny out of the car and outside.

Bill V · #8 (**permalink**) 07-14-2006, 11:33 AM

The yellow green paint you're referring to is zinc chromate. Not very pretty, but is an excellent anti-corrosive. You're on the right track there.

http://www.paintcenter.org/rj/jul02k.cfm

Ant · #9 (**permalink**) 07-14-2006, 11:55 AM

I guess my trans is just oxidising a bit, and WD40 as John mentioned is simple fix and can be applied easily and when necessary! Also not knowing how quick this issue with Magnesium oxidation, progresses due to getting the trans wet etc, it may not be a problem at all.
WD40 is probably like a good Firearm CLP protectant so any will do!

double ugly · #10 (**permalink**) 07-14-2006, 01:23 PM

I had Dymag wheels on my Atlantic formula cars in the 80s. I had them powder coated because, even though they were plated, the magnesium started to corrode when the plating wore thin. The WD40 really doesn't leave much of an oily residue. Spray it on and wipe it off.
I did this with a Sunburst rim I use for a spare. It brought back the original finish after I bead blasted the rim.
John