[bmwhitman]

I was removing the coolant hose that is connected to the engine. I had to remove the "Double Holder" bracket supporting the hose by removing two aluminum screws attached to the engine. While I was reinstalling the screw I over torqued the screw and the head of the screw snapped off. Now I only have one screw support this bracket. The other screw stem is still inside the engine. Is it possible to remove the broken screw from the engine?

I've attached a picture where you can see the one of the screw missing from the bracket holding up the hose (yellow arrow). The screw is inside the engine.

[abeardo83]

Only thing i can think of is trying to drill it out. If it's Aluminium, it should be pretty soft.
Use a bit that is smaller than the screw shank. If you can drill through it, it'll crumble away from the threads once it's small enough.

[robthewrench]

If you have good access around the area, you can try to use an 'easy-out' reverse bolt extractor. You should be able to find some basic sizes at hardware stores. More unusual sizes will need to be ordered.

An easy-out has 3 parts and is a two step process. The parts are a size matched drill bit and extractor bit. The third required piece is a t-handle wrench with adjustable shank. Choose an easy out that is smaller in diameter than the bolt you are trying to remove. The drill bit and extractor bit usually come packaged together, but you have to buy the T handle (or tap) wrench separately. You can google how to use these.

Step 1: Using the drill bit, drill into the broken bolt. Try to drill the hole in the exact center of the bolt. Use oil or wax to lubricate the drilling process. It is better to make the hole deeper, but not longer than the length of the broken bolt. The hole must be well centered and run parallel to the bolt. Soak the bolt in the PB blaster or liquid wrench to make it easier to remove.

Step 2: Using the extractor and the T handle wrench, screw the extractor into the hole COUNTER-CLOCKWISE. Do this slowly and with pressure forcing the extractor into the hole. The extractor is larger than the hole and will stop when it fills the whole. With even pressure, continue to try and turn the extractor counter clockwise. Hopefully the whole bolt will now loosen and come out.

It is not uncommon to break the extractor. They are made of very hard, but brittle, sintered metal. You might want to buy 2.

[Efthreeoh]

If the screw broke flush with the engine block, then an easyout should work. If the screw is protruding from the block, you can grab it with vise grips and get it out. There is a great tool for stud removal, which is like a drill chuck that grabs onto the stud and tightens as you turn it counterclockwise to remove the stud.

Good luck.

[timograham]

I also broke this screw on a 2006 325xi. Perhaps the aluminum screw should not be reused or perhaps I just over-torqued it.

I was unable to extract the screw with left-handed drill bits and extractors. The extractors cut through the soft aluminum. I don't think I drilled it quite in the center which may have contributed to the failure.

I ended up drilling out most of the screw, then I tried retapping the hole at the original M6x1.0 size. This also failed (again perhaps because I was slightly off-center), and now I have a hole that is just slightly larger than the screw threads.

I'm considering trying an "M6x1.0 Thread Repair Kit" with stainless steel thread inserts. Does this seem appropriate? Any alternative for this sort of repair?

[timograham]

I'm concerned that a stainless steel insert in the N52's magnesium engine block with an aluminum bolt is a risk for galvanic corrosion.

The BMW service manual seems to suggest so:

No steel screws/bolts may be used due to the threat of electrochemical corrosion. A magnesium crankcase requires aluminium screws/bolts exclusively.

and later:

Screw in aluminium Helicoil

Elsewhere on the web, I've read:
- "Yes, it is true that severe galvanic attack will occur if magnesium and stainless steel are connected in the presence of an electrolyte."
- "To prevent galvanic corrosion Cadmium is plated on stainless hardware that is inserted in aluminum or magnesium castings."
- "Aerospace practice is to put [helicoils] in "wet" with zinc chromate primer or epoxy to minimize galvanic corrosion between the steel insert and the non-ferrous alloys."
- "One of the requirements for galvanic action is the presence of an electrolite, and in our case that is usually water. Luckly, most of us don't let our cars sit out in the rain all of the time, so moisture trapped in the threads isn't all that prevalent a problem. Still, the use of a primer as a sealant isn't a bad idea!"

The advertising for HeliCoil says they "work in any part of material - aluminum, magnesium, cast iron, bronze, etc."

I see BMW offers an "Alu-Heli-Coil Threaded Insert" in various sizes, however, they are about $30 each! M6 sizes are M6x12 and M6x15. In this case, it seems the latter number refers to the length rather than the pitch. Elsewhere I read, "Whenever the pitch dimension is omitted from a metric bolt specification then the bolt is always coarse threaded." Another chart I looked at listed M6x1.0 as coarse, so I guess these inserts would work.

I haven't found aluminum threaded inserts on Amazon or elsewhere. $30 for an aluminum insert from BMW seems like a lot when you can get a kit with stainless inserts, drill bit, tap, and insert tools for $13.

I lean toward using a stainless insert considering:
1) this area is unlikely to see a lot of water
2) this isn't an extremely critical screw
3) the screw may never need to be removed again in the life of the car

[timograham]

I received this advice, "The tricky part about the galvanic corrosion is that it isn’t necessarily localized to the interface between the metals and could occur anywhere on the engine block as long as there was an electrical potential being facilitated by the electrolyte."

To be safe, I purchased TIMESERT's M6x1.0 KIT with 9.4mm Aluminum inserts & tap guide p/n 1610B-ALU for $99 + shipping. Installation was easy. The kit includes 5 inserts and the installation tools. Since I only used one insert, I'll resell the rest of the kit to recover some cost.