7R Case Welding
 

I've got a recently acquired 7R case that has the material around the stud at the bottom rear of the case partially broke off. I've got experience welding aluminum, but have never done magnesium. The damage is all external and relatively minor (but the bolt/stud won't hold any tension as is).

I'm using a Lincoln Square Wave Tig 175 machine; any suggestions as to filler rod, settings, gas flow, etc.?

What alloy is 7R made of? A Heliarc handbook I've got mentions a couple of different alloys.

Thanks,
Francis Kennette
'74 Carrera (euro)

Check with your local Lincoln dealer, mine was very helpful in setting me up for various aluminium as well as stainless steel alloys. I'm at home now but I also have a professional welder's handbook at work, I'll check it and get back to you.

I haven't welded magnesium myself, but I do know that it will catch on fire if heated up to a certain temperature. I'm not sure if this can happen when working on a localized area, but I would do some more research first before any attempts.

-Wayne

It can definitely be done. My 2.7 case has a weld repair at the bottom of a head stud. Made me uneasy but the stud has been in there for a long time and has not failed. Like Wayne, I thought it burned quite well. I remember setting magnesium on fire in Science lab at school. I thought it produced it's own oxygen as a by-product and thus furiously fueled the fire. BUT that was 20 years ago and I could be VERY wrong. Also, this was pure magnesium and not an alloy.

Tristan

I lit up the pulled material from my studs with a blow torch (MAPP) and it definitely burned! Must be a question of actual temperature?

I know they can be welded -a pc of mine on the main bng broke on the dowling jig and 'Clewit'found a place to fix it ,so ask rich if you want.........I now he has the ans.

Yes magnesium can be safely welded. The TIG welder uses Argon gas to shield the weld from oxygen in the atmosphere. Magnesium does not produce its own oxygen because, like oxygen, it too is an element.

I just finished welding a Hewland transmission case, which is actually a VW type I case. Magnesium flows worse than aluminum. Really gummy and difficult to get the puddle to move.

You will need to clean, clean, clean the base metal. Magnesium is shiny silver like aluminum when cleaned (the dull gray color you usually see is an oxide). I used American Welding Standard (AWS) number ER AZ92A filler rod. AC setting on the TIG just as you would aluminum. I preheated my case to 400 degrees F prior to welding. The result was a non porous big ugly weld on the bell housing that just finished it's third race this weekend without cracking. So far so good. BTW this housing is on a Formula Continental.

Good luck,
neilca

Neil,

Good info. Can you tell me the best way to remove the magnesium oxide? I have it on my case mating surfaces and the scotchbrite and brake cleaner method is painful...and giving me a rightous buzz!

Thanks
Tristan

Sand paper. I sanded and ground the surface. I had to "V" the crack due to the thickness and need for good penetration. You will need to have the spigot hole machined after welding because you will probably have a big glob were your weld is.

neilca

Tristan,
I'd recommend you proceed very carefully on that parting line - you do not need a bright shine on the halves to get a good bond with the 574 and if you start going after the gasket surface with sandpaper, you can very likely do more damage than good.

Thanks for the responses guys (especially Neil - I watch the FC/F2000 site regularly and was thinking of asking the same question there),

I know from welding aluminum that cleanliness is ultra important; I keep a stainless steel wire brush specifically for aluminum welding and also usually use a chemical aluminum cleaner (Formula 512M - given to me by brother-in-law many years ago)that is used to clean aircraft aluminum - really brightens things up.

I cleaned my case parting line w/ scotchbrite pads but found lacquer thinner &/or acetone worked better than carb cleaner; if you don't like the fumes wear a paint style respirator.

I intend to do a short practice on one of the old timing chain covers I have from an engine I updated to pressure fed tensioners; does anyone know if these are the same magnesium as the case?

My biggest hurdle right now is finding a weld shop that carries small qty of magnesium TIG rod - my usual supplier has a min 1kg at C$168/kg, or I can order min 3lb at Weldmold in Detroit at US$68.51/lb for 3/32", $43.15/lb for 1/8" (don't you think the per lb price should be the same regardless of diameter?). If I don't find a few rods soon I'll bite on the minimum order qty and maybe I can weld a mag case for somebody else someday.

Thanks again
Francis

Francis,
The guy I welded that case for had to buy a bunch of rod he will never use. I will call him today and see if he will sell you some.
neil

Francis,

Talked to the guy with the rods. He said he would sell you all you want for $2 per rod plus the shipping.

Let me know,
neil

Dave,

Thanks for the advice. What about the oxide on the case where the main bearings interface?

Tristan

You mean the saddles themselves where the bearing shells are inserted? Just rub out with a scotch-brite pad and solvent like the rest of the case. The mains should be free of loose soil and clean so that the bearings seat properly and the oil doesn't pick up any particulate. Other than that, a high shine is not required. Magnesium, like aluminum, has a rapid-forming coat of oxide on the surface naturally. It is not a 'bad thing'. Electrolysis, which corrodes away at the case and causes the pitting you probably see in some areas, is another issue.