Welding Tips and Tricks

I have a 2008 BMW 650i, & while working on it recently I snapped a bolt in the block. Then when I tried to use an extractor I snapped the extractor in the bolt! To top it off he bolt was in a very inconvenient spot (underneath the exhaust manifold). So, now at this point I pulled the motor so that I could get a clean shot at drilling the bolt out. I knew that the block was magnesium. I had no experience working with this material before, but I had heard that it was similar to aluminum. So I went ahead & proceeded to attempt to drill the bolt out as carefully and straight as possible. With the bolt being a harder material than the surrounding material & the extractor being even harder than both, it turned out to be an impossible task. The drill bit was wandering around sideways trying to get through the softer material first. I did manage to get the bolt & extractor out, but in the process I went from an 8mm wide hole to probably a 12mm wide hole that is approximately 7mm deep.

My next solution is where I need advice from any of you that can help point me in the right direction.

I plan to fill the hole using the TIG welding process. Then drill & tap the hole. I have limited experience MIG welding, but zero experience TIG welding. Luckily I have a few spare parts from the motor such as the timing case cover that I plan to use to practice on.

Please correct me if I'm wrong, but according to some reading that I've done I need to use a TIG machine that is capable of AC welding at 125a & that it is a plus if it has pulse welding capabilities. So I recently purchased a WeldPro Digital TIG 200GD. I don't know what the exact composition of the magnesium alloy is so I purchased some AZ101 filler rod because it is supposed to be a good general use magnesium filler rod. I need to find out which tungsten to use, & what is the ideal shielding gas I should use. I also could use some suggestions about the settings of the welder.

Any help is greatly appreciated, thank you in advance.

Tungsten recommendation is 2% Lathanated (blue) in 3/32”. Use a good gas lens. Pure argon for gas.

Good luck with that repair.

If it were me... I’d tap the current hole to 12mm 1.75 pitch. Then thread a piece of pure magnesium in (buy some 12mm rod, thread it with a die.) Use some Green LocTite. Let set up. Then carefully drill a new pilot hole for your 8mm 1.25 hole. ALWAYS use a center punch to drill, especially into broken bolts. A carbide bit might have been a better choice but too late for that now.

By installing a threaded “plug” your new threaded hole will tighten the plug to the head as you snug up the original bolt. No blind welding needed.

Hate to be a Debbie Downer, but sometimes injecting some reality is a good thing. The repair welding you're talking about is advanced TIG welding. You mentioned that you have zero TIG experience and very limited MIG experience, so this repair is likely well out of your scope for the near term.

You can absolutely do this repair yourself, but you will first need to spend several week learning the basics of TIG welding, and then you will have to spend at least a few months after that TIG welding each day (or at least several times each week) in order to hone the skill and get to the level where you can adequately do an advanced repair. Otherwise it will not go well for you at all.

So I see your options as this: Follow CJs advice and do a plug, take the part to an experienced welder and have them do the repair, or spend the considerable amount of time to learn TIG welding and then do the repair yourself a few months from now.

Just giving you a dose of honesty here. Good luck, and I do hope that you take the time to both learn and then master TIG welding.

what cj said.

do what cJ said

em3doc wrote:Please correct me if I'm wrong, but according to some reading that I've done I need to use a TIG machine that is capable of AC welding at 125a

Not even close. 125A won't even tickle it. Like Spartan said, this is TIG Welding 9003, PhD level, for this kind of task. IF you really want to do this. Buy 2 or 3 junk blocks. Smash each and every threaded boss and bolt hole to smithereens. Then repair them all. By the time you finish the 3rd engine block (and hopefully develop the proper technique to accomplish the task), you'll have enough knowledge to attempt your working motor with a high degree of success.

Some form of threaded insert is much more likely to succeed in this situation. A couple of potential suppliers of metric series heavy duty key-locking inserts are --

Keensert (check URL= https://www.clarendonsf.com/products/in ... /knhm8x125)

Acme Industrial (check URL= https://acmeindustrial.com/industrial-s ... size-kits/)

These appear to be the right size range (8mm internal thread insert has a 14mm external thread).

PS -- I would be very surprised if BMW made an engine block of Magnesium alloy, most likely an aluminum alloy for an engine. Transmission case might be a mag alloy (ala VW Beetles for decades).

Leejohnson1313 wrote:PS -- I would be very surprised if BMW made an engine block of Magnesium alloy, most likely an aluminum alloy for an engine. Transmission case might be a mag alloy (ala VW Beetles for decades).

Me too but I didn't wanna say anything because I'm not an expert in that area.

Leejohnson1313 wrote:Some form of threaded insert is much more likely to succeed in this situation. A couple of potential suppliers of metric series heavy duty key-locking inserts are --

Keensert (check URL= https://www.clarendonsf.com/products/in ... /knhm8x125)

Acme Industrial (check URL= https://acmeindustrial.com/industrial-s ... size-kits/)

These appear to be the right size range (8mm internal thread insert has a 14mm external thread).

PS -- I would be very surprised if BMW made an engine block of Magnesium alloy, most likely an aluminum alloy for an engine. Transmission case might be a mag alloy (ala VW Beetles for decades).

As you probably know you can test for magnesium by cleaning a spot and put white vinegar on it and it will foam up.
Aluminum will not.

Leejohnson1313 wrote: PS -- I would be very surprised if BMW made an engine block of Magnesium alloy, most likely an aluminum alloy for an engine. Transmission case might be a mag alloy (ala VW Beetles for decades).

Per online specs, it does appear to be aluminum, not magnesium. Repair advice still holds true.

I would drill and tap it and install a helicoil. What does the bolt hold to the block? 8mm is a fairly small bolt. You might have to open up the mount hole on whatever you're mounting to use a 10mm or 12mm bolt with helicoil.

cj737 wrote:

Leejohnson1313 wrote: PS -- I would be very surprised if BMW made an engine block of Magnesium alloy, most likely an aluminum alloy for an engine. Transmission case might be a mag alloy (ala VW Beetles for decades).

Per online specs, it does appear to be aluminum, not magnesium. Repair advice still holds true.

Nope, a quick online search turns up that it is indeed a magnesium/aluminum alloy. So, quite a bit different than just regular aluminum cast.

Appears the preheat must be quite high and needs the some control over the temp. Just going by what I could find quickly online, but this doesn't look like a beginner repair.

There were also comments I saw about them still being flammable, though that sort of thing is rare. Pure magnesium certainly isn't something you want to light up on... But I have no idea what this stuff is.

Might opt for the twinsert or helicoil route...

PS. In the future, when drilling a broken bolt, get a center mark as close as is humanly possible. Flatten the top of the broken bolt if you can. Then, use a drill guide (you can drill one yourself in the size of the drill you're going to use). Locate that over the bolt and hold it fast so you can use it like a drill bushing. DRILL THE HOLE VERY SMALL. Do not under any circumstance attempt to drill at the nominal tap drill size on the first go. Drill with a VERY small drill. That way, it won't find a soft edge and lead off. If you do it this way you can miss the center by quite a bit and still save the day.

Now, stepping up in drill sizes a little at a time, keep drilling till you DO hit some soft material, and stop there. Now extract the pieces of bolt. That'll work much better than hogging out the softer metal while trying to remove the hard bolt.

All the advice posted in the last couple of days is nice, but the OP hasn't been back since 1 Feb.

from what I've been seeing, the bolt isn't doing a lot of work. Like some kind of tensioning bracket which the OP doesn't tell us. Also, if this is his only means of transportation, he's doing a lot of walking or bicycling to get parts