2005 Chevrolet Cobalt keyway

What is the problem? Is it tight or is it just sheared off and impossible to grab? Most of the time they can be nudged out with a small punch and hammer. If it's too tight for that but the slot isn't all chewed up, consider using a wire-feed welder to weld a steel bar onto the key. Put a strip of masking tape on each side of the slot. It will burn away, but it will last long enough to prevent any spatter from sticking to the crank snout. This job takes about two or three seconds. That's not enough time for the crank to get hot enough to damage the seal. To be extra cautious, you can stick a piece of sheet metal in front of the seal to protect it. Let the bar cool down a little before you try to pull the key out. If you have to, tap on the bar with a hammer. If you weld like I do, when the bar breaks off, weld it on again, but if you're lucky, the weld will build up on the key so you have something more substantial to work with.

As a last resort, especially if the slot is mangled, use a small Dremel rotary tool with small grinding wheel to carve away anything that isn't "slot". Start from the middle. That may allow the two halves to fall out and leave the slot undamaged. You can still use the tool to true up the sides of the slot if the new key doesn't fit easily.

I'm not familiar with your specific engine, but I've never seen a key way that's buried where you can't get at it. GM engineers are always dreaming up new ways of doing things but I don't think even they would need to make the slot inaccessible.

If it is tucked in where you can't weld to it, you have nothing to lose by trying some epoxy. Wash the dirt and oil off first with brake parts cleaner or carburetor cleaner, then glue a small metal rod to the remaining part of the key. You'll probably want to sneak that masking tape I mentioned in there with a needle nose pliers so you don't get glue on the crankshaft.

This trick works well for keys that are broken off in the ignition switch, but you need to slide two small pieces of paper in there first to prevent gluing the key to the cylinder!