I'm sceptical of welding nut because of the aluminum block acting as large heat sink lol!
It works. It actually takes more heat (higher power) to weld aluminum due to it being a better conductor.
When studs are broken off 'flush' is when a guy can use the tack-on-nut procedure. Ideally you want to tack near the peremeter of the stud (where you get the most benefit of torque transfer), rather than the center.
To be more precise on the procedure, because I've probably done it a couple dozen times (and think I have a pretty good success rate now): I prefer to take the welder and precisely and carefully lay a bead of weld onto the portion of the stud (sticking out or flush). Strike the arc in the center of the stud and work a circle from the center out, making sure the final round puts a good bead on the perimeter of the stud (inside perimeter). Start in the center because you can see what you're doing once strike the arc. Once I feel good I made good penetration and a 'strong' weld, then and only then, lay the nut on top and weld it to the stud. Making a pre-weld onto the stud allows ya to concentrate on getting a good strong bead on the stud, not having to worry about the nut. Then weld the nut on afterwards. It works like magic once ya figure out a good technique.
It might be a little difficult to do it on the side of the block and a guy would probably want to lay a welding blanket around so you don't get spatter or any burning where you don't want it. Also, because you want to work pretty quick, I sometimes find it helpful to tach a piece of rod onto the nut ahead of time so I can quickly grab the rod/nut ...and hold it over the stud and start welding ..and not have to fumble with my fingers in a tight area. Then just cut the rod off once the nut is welded to the stud ...and remove the whole thing with a wrench/socket.
It's easy to practice, for guys not familiar. Just put a piece of 3/8" rod in a vice and weld a nut to it. Tighten the vice and see how strong your weld is. If you have a piece of aluminum bar laying around (1/2" thick or greater) you can tap or drill a hole and try it with the aluminum and see if your technique ruins the aluminum ...and adjust your heat and technique accordingly. Then you won't be nervous doing it on the engine.
If ya don't have a welder, drilling works too. The welding trick is still a good tip to keep in mind b/c where ya have a rusted/siezed bolt/stud, the welding works way better than a brittle EZ-Out. The heat helps loosen up the bolt/stud.
Another tip: ...if an EZ-Out should break in a bolt/stud while trying to remove? ...another trick is to hit the remaining part with a #1 tip of an acetylene torch. The high strength steel (too hard to really re-drill) will sparkle and melt away like a sparkler.
