Hey everyone! Looking to get some input on the severity of a crack I found on my magnesium case (middle bolt). Luckily, it's not in a position where oil might leak, and it doesn't seem "all that critical" to me, but since I'm no expert, I'd appreciate a second opinion on this, and how to fix if necessary. Everything else seems fine and the engine runs very well. Found it while taking out the alternator which died.
Thanks!

 

You may want to post this over the Pelican 911 engine rebuilding forum, as there are some experts (e.g., Henry Schmidt) who are on there regularly and could give high quality advice.

My low-quality comments are: Magnesium is weldable, so my guess is that the likely way to repair is to remove the stud, grind away the cracked area, re-weld and then either thread for the stud directly or put in a Timesert. BUT, I am pretty sure this is only feasible with the case disassembled and would likely also require the case to be refaced, mains align bored etc. Basically all the stuff that would be done during a comprehensive rebuild (where all the "usual" mag case machine work in done). Since your engine is running well, the best advice may be to leave it, but monitor it for now and hopefully defer it to the time when you do want to do a rebuild anyway.

Take that with a grain of salt though. I know welding, and I have rebuilt an aluminum-case 911 engine (much easier than mag case I think), so I know a little more than nothing, but well short of actual experts.

 

Is it cracked or just delaminated from corrosion ?
Seems like a fair amount of corrosion on the case.My guess is the engine would have to be disassembled to have a decent weld repair.
From what i know about welding aluminum and magnesium engine cases , it would need to be stress relieved before attempting to repair it in order
to prevent warpage !
I’m sure a professional welder could give you a better opinion.

Cheers
Phil

 

It is corrosion resulting from a minor crack. The elements got in and started to break down the material. It could be early enough but hard to say. I would poke around a little but carefully and see if it extends much further into the case. If just starting it is possible to clean and protect but I wouldn't allow it to continue. If there is significant enough material the case might be able to be weld repaired but not a fan. All the white spots are the signs of corrosion down to the dendritic level and should be cleaned. If allowed to progress the case will be compromised. A proper cleaning and preservation shopuld be considered but blasting the case outer surface will just break down the material more.

Welding mag is different than welding aluminum. The case would need to be disassembled. All the bad material would need to be ground away and they would need similar composition filler rod. Clamp the mating side to a flat surface to prevent warping and heat the area to about 500 degrees F slowly. then you can weld. Normally the temper is ruined but heat treating this over wouldn't be wise.

Not sure if you can see this. These are the wind diverters from a 964 engine made from mag alloy. You can see hopefully where the white pitting began and after media blasting the material is gone. This is what is happening to your engine currently and will only get worse if not treated.




I am using these on an engine I am not concerned over. However I don't want them to get worse. I understand you can't do this to your case. But I used an acid etching primer on them prior to painting.

Normally the best way to eliminate the corrosion is by using what is called a Dow 7 or acid pickle treatment. This will etch away the contamination and the Sodium Bichromate will bond with the surface to create a protective coating. However since the oxide skin from the casting process is gone the case will need to be preserved using some method. Many vintage race cars paint the parts but that is up to you.

There are some products out there that make claims of protecting magnesium but I have not used them and I wasn't allowed to use them on the parts I manufactured for the DoD.

 

Clean it up and put some waxoyl or other coating on it. When you rebuild your engine you can evaluate better. I use Wurth HHS 2000 on my fan and other corrosion prone areas. Magnesium want s to turn to dust.

 

Really? After manufacturing complex magnesium sand castings for the aerospace industry for 30 years and seeing the effects of these products used incorrectly I would reconsider. Without proper cleaning of the surface first it will continue to corrode. That is akin to putting a bandaid on a dirty surface and expecting it to stick. The reason why most fans fail is the paint chipping and moisture getting under the surface and you get a form of flash corrosion which will just continue to attack the material. Magnesium is very durable and will last a long time if properly conditioned and protected but once it is allowed to corrode will continue to if not cleaned and cared for properly.

I

 

Neither the blocks nor the fans or gearboxes were painted on the early cars. Everything was black oxide treated and then everything was sprayed with tectyl. Basically a waxy oil to keep corrosion at bay.
Normally the parts clean up nicely if blasted then resprayed with some similar sealant. At least the corrosion should not advance.

 

Yes but they retained their natural oxide coating from the casting process. Once this is damaged it is no longer safe and will corrode quickly.

I had to do extensive corrosion testing, 5 days min in a salt fog bath, on my castings especially for the Sikorsky Seahawk the black hawk got a lesser purity alloy. The difference how magnesium reacts with and without its natural oxide coating is significant. It takes years to break down the natural oxide coating but only hours to start after the oxide coating is removed. A loss of roughly 50MPY is seen on castings with an oxide coating and without we would see 5-10x as much. Proper chemical conversion of he alloy would bring rates down to 2-5MPY loss. Depending on the alloy and the combination of trace elements iron, manganese and copper will determine how much and quickly the material will corrode. In this case the higher purity alloys weren't available yet.

 

Cobalt is spot on … i’m in the aeronautics industry as well and different alloys have different reactions to corrosion, in the case of magnesium there are specific steps
to follow , and the first thing i would suggest is to blend out the damage and do a fluorescent crack inspection afterwards to evaluate the extent of the damage.
Magnesium needs to be welded by a professional welder who has the knowledge of such a material !

Just sayin …

Cheers
Phil

 

Are you specifically addressing the use of non-hardening, tenacious wax or oil based substances which continuously creep into crevices? I can understand how a paint layer can become partially separated from the substrate and trap moisture and accelerate corrosion, but it seems to me more likely that applying some cosmoline, fluid film or waxoyl at the crack area is more likely to help than hinder.

Or course tearing it all down, removing damaged areas, re-welding (right alloy right process), post machining etc. is the optimum approach, but the OP has an engine that is currently running well. What would be your recommendation for a intermediate strategy that could be done now and in the interim until such a time the engine would be rebuilt?

Not asking in an argumentative way, rather, I can tell with your deep foundry expertise you have greater specific expertise in this area of materials science then I do and will have better ideas on this.

 

fill it with jb weld , lightly sand , clean up top of case , hit it with shark bite or some other sealer. , put alternator back in .. never look at it again lol.

 

Cobalt is correct that once the black oxide has been removed corrosion starts quickly. However if cleaned up and coated with a Tectyl type preventative he can enjoy the engine for quite a few years until he tears it down for a rebuild.
The HHS goes on liquid and sets to a waxy consistency and resists heat fairly well. If you can get tectyl, even better.
It looks to me as if someone used an aggressive engine cleaner and did not rinse it off well.
Here is the same area on my car and the fan treated with HHS

 

Thank you everyone for the responses! I tend to be a bit on the over-cautious side of things and seeing spots like that on the case really made me nervous My plan now is to brush the oxidation off, clean it thoroughly and apply a coating over it. I've ordered HHS because a lot of stuff thats suggested on the forums isn't available here in Slovenia. Some parts are very difficult to get, but with a bit of ingenuity I'll probably be able to reach most of the top part of the block, and the car is going on a lift to do the underside as well, though that seems in great shape from just looking underneath. On the top part, the corrosion does seem to only be concentrated on the middle of the block, where I'd also assume that's where the fan blows directly on it.

I'd really hate to take the engine out, because she runs like a dream; good power and no starting issues or smoke.

 

I was busy but I love how 3 generations of magnesium manufacturing and the pioneering of several magnesium alloys including contributing to the proper chemical conversion and preservation of magnesium alloys is useless here. I spent 30 years X-raying, Fluorescent dye penetrant inspecting and manufacturing the most complicated magnesium castings I oversaw the manufacture of. Our cage code was older than Boeings. I have volumes of documentation my grandfather hand wrote as he headed Bendix Eclipse Pioneer program and employed nearly 3000 employees. He turned over his R&D to the federal government and I have letters expressing gratitude for saving the country and reducing scrap on a Nation wide average by 40% allowing us to build the aircraft that helped win the war. Bendix alone was producing 1 million pounds of magnesium and 2 million pounds of aluminum castings in Teterboro NJ.

It is an interesting read and his R&D is still part of the industry standards of today.

I highly recommend at a min checking to see how significant the corrosion on that boss is. As you can see it is far different than what rstaga posted. I always say take the least invasive approach first. From my experience the extent of the corrosion can be easily determined by just poking at it with a pic or sharp utensil. The material will either flake apart (it becomes powdery) or it will just loose a small top layer. That would be what I use to make a decision and move on from there. If it is so far gone it flakes apart you know you have to do something if not at a min I would get in their with a wire brush preferably something non marring like brass wire. and clean the surface of as much of the corrosion including the white spots. The white spots unlike what rstarga believes is corrosion already breaking through the oxide layer and breaking down the material. You will find the case surface is full of damaged areas where each white spot is. Once you clean it properly then you can coat it with something if that is what you choose to do. The products mentioned are great for clean material and but not designed to be used on anything but a clean surface.

Many manufacturer's used magnesium years ago without properly preserving the material including Porsche. Lamborghini used to use cast magnesium for coolant tubes which always failed. Ferrari's cases were prone to this exact same type of failure. I made many automotive replacement parts for a friend Joe Nestasi of Nastasi racing. He sold Lamborghini to Iacocca. I made the yellow colored pieces on his famous typo 33/3 which is one of the most significant race cars in history of racing and he would try to trade me corroded Ferrari Engine cases for new parts. I took a few that had similar failure spots and what I found varies from minimal concern to disturbing. In most cases the case could have easily been preserved but the shops just applied some waxy coating which eventually lead to excessive corrosion and catastrophic failure.

My point is just don't coat and cover it is best to inspect first and then make a judgement call on how to proceed.

 

@cobalt Thanks for the detailed answer! I did some light brushing and it seems like its more or less still at the surface. Also tried poking it with the sharp end of the brush and its really solid, definitely not brittle. It's also not as blue in real life as on the picture, don't know why the phone camera does this, and they say the iphones are supposed be accurate

I'll clean it more and get as much of it off as possible before wiping it down with something to degrease it before applying a coating. I've read a bunch of forums and some research papers and it seems white spirit should work fine without causing damage to the case. After that, Wurth HHS 5000 seems like a good product - water resistant, acid resistant, plus it contains a small amount of teflon.

Also, you have some really cool work experience there!