Originally Posted by Twin-shocker
You can generally weld mag with commonly available rods no problem. However if this proves to be impossible, then get a scrap case and cut this up to make filler material. Repairing with epoxy makes welding much more difficult, as its very hard to get rid of the epoxy completely before welding.
Sorry for my slow reply on this.
As mentioned above, I used a so called "general purpose" magnesium rod I got from the welding supply shop several years ago. I have only welded magnesium a few times but have generally found it to be more challenging to weld than aluminum and even more sensitive to contaminants such as oil.
Although I did try to clean my clutch cover thoroughly, there may still have been some oil residue deep within the pores of the crack I was repairing. I believe this to be the case as I was experiencing some outgassing in the puddle while welding and the outgassing left behind some pitting in the weld.
I was also getting a fair amount of soot while welding even though I turned up the flow meter a good bit more than what I use for aluminum.
Later I found this helpful youtube video on welding magnesium. They seem to recommend keeping the tungstun electrode very close to the puddle as you weld. Perhaps this gives better shielding. I dont think I was as close as shown in the video.
I used straight argon. I think this is perferred over a lower cost nitrogen/argon mix often used when welding steel.
Here is the youtube link.
Below is a photo of my repaired cover. I put extra filler into the area of the kick shaft bore for added support. It is not too pretty (note the pitting) but it did not leak either. The photo was taken after the bike was laying in the rainy ditch for a couple of days after being recovered from being stolen. It looks especially bad as my polished mag cover was already reacting with the moisture.
Compare above with an original cover for an idea of the extra filler added,
Twinshocker suggests that pieces from another cover be used as filler rod. This is something I would like to try as the pitting could also be due to a mismatch with the rod that I used.
Hope this helps!