Best way to Clean (exterior) a 914 Transmission, I am about to have it Evil rebuilt (third one is a charm) and want to Options

[Dr Evil]

Cases are mag ALLOY not pure mag. I have used Easy-Off oven cleaner for years with no problems.

[pcar916]

Cleaning mag and mag alloys is done by many industry folks using Stoddards cleaner, which seems to be a mineral spirit blend of some sort. The original cases were, and still are, pickled (acid) first and coated with Tectyl. I can find it on the worldwide websites but it's only available in the US through Daubert Chemical as Tectyl 553. I can't locate a supplier that will sell small amounts.

http://www.daubertchemical.com/main.taf?er...productLineId=1

Since the coating is supposed to not only reduce oxidation, but also seal the case, I thought that maybe CRC had something. They do, but it's equally hard to find. It's a spray-on aviation sealer / anti-corrosion stuff.

http://www.crcindustries.com/ei/content/pr...N=10200&S=Y

It's hard to find too. Darned frustrating since I'd like to seal these cases with the same technology the factory uses!

Both of these eventually wear off but can be reapplied. Anybody know a source for either one?

[Cupomeat]

Well, looks like I should have waited about 2 more days before I acted...

I did the easyoff thing and now have no idea what to do.

It will be going to Dr, Evil on Friday, so I suppose i can do nothing for a while...

Thanks guys for all the information, always a wealth of it here.

[Rand]

I'm curious... Does someone have a photo of a 901 that was cleaned with oven cleaner some time back, and never retreated in any way with paint or sealant of any kind? How does it look now?

Ken raises a valid concern. Eric hears it after it's too late. Others indicate it's nothing to worry about. So, let's get to the bottom of this.

[Katmanken]

A coupla points:

First:- About mag corrosion from the internet....

"And while the corrosion rates of modern, high-grade magnesium alloys are acceptable for interior applications, the automotive exterior environments are extremely harsh for bare and even coated magnesium parts.

The interface between the steel bracket and a magnesium-alloy casting is prone to galvanic corrosion.
First, road salts and slurries can easily damage conventional electrocoat paints, creating sites for rapid electrochemical dissolution of magnesium. Second, being the most reactive (or anodic) metal in the electrochemical series, magnesium is prone to severe galvanic attack when in contact with other metals. In automotive structural components such as engine cradles, road salts and debris can accumulate around the bolts and washers that mechanically affix magnesium parts to the car frame. Such sites may become prone to galvanic corrosion (see Figure 2).

Therefore, finding cost-effective solutions for protecting magnesium alloys from corrosion has become paramount.

One of the best ways to combat galvanic corrosion of magnesium is to use isolation materials to prevent direct contact between bare magnesium and the dissimilar metal. If a high torque load is required, such isolation materials must be made of special metals or other inorganic substances that minimize excessive deformation upon loading. In particular, the use of aluminum washers can significantly reduce magnesium corrosion; however, the effectiveness of such corrosion protection is directly related to the chemical composition of the aluminum washer being used (see Figure 3). "

Now for protection:

My mag book suggested elements higher in the periodic table such as zinc to act as a sacrificial anode...

And according to the pelican 911 board....

The Factory Workshop Manual (Vol. I, page SR 140) sez:

“Warning:
Pressure cast parts must not be cleaned with acid, since acids attack the magnesium alloy. After any transmission repairs during which the one-season underseal is washed off the gearbox housing, or when the underneath of the vehicle is washed, we recommend that corrosion protection be improved on the pressure-cast gearbox housing by applying a bitumen or wax based one-season underseal, e. g. Tectyl, which should be sprayed or brushed on.”
© Dr. Ing. h.c. F. Porsche Workshop Manual, Vol. I, Page SR 140.


Tectyl in the wax formuation sounds a lot like cosmoline- the honey colored wax based wax protective coating that''s been around since at least WWII. A lot of european cars are shipped coated in "cosmoline" for protection and it's cleaned off with mineral spirits and a rag. If they didn't clean the tranny, that would explain the coating.

I'm sure there are other wax cosmoline or panel wax materials that look like the Tectyl....

[Rand]

(IMG:style_emoticons/default/thisthreadisworthlesswithoutpics.gif)
Rust: No issue, this metal doesn't rust
Corrosion: Yes, it does. Detail the results: Darkish? Spread? We know it won't eat through the case, so it's a visual surface issue. Valid of course. Show us pics!

[Dr Evil]

I wish I had pics of some of the shit boxes I have seen on the East Coast. There is definite exfoliating corrosion that goes on in the rust belt. I have seen tail cones that have no flat surfaces for the washers and nuts to seat against. When in CA, I NEVER saw anything like this. Salt, is the big contributor. Transmissions that I have received from FL from TC that have had sand and rust in side of them actually looked just fine on the outside. There is no way that the amounts of rust I have seen could be possible without the whole gear box being subjected to water over a very long period of time. There are pics of these gear boxes in their own threads as they were terrible enough to mention. The last one looked very clean on the outside, so much so that I was very surprised to find the insides completely rusted solid and rust flakes falling out of the case like sand.