I've got an alan key bolt (hex key) going into aluminium with the hex part stripped out, I need to get it out to reach an oil leak. I tried drilling down the middle and using a screw extractor, but the screw extractor wont grip, and just chews up the bolt even more. The bolt itself is in very tight.
Any ideas?

You could try putting another bolt insice the stripped out part of the hex bolt and welding it together then just undoing the bolt ,being welded together it should come out .Iv'e done this a couple of times with stripped bolts and it has always worked.
Good luck

OK..

I take it from your strategies used, that the hex bolt is countersunk? This is why some vicegrips weren't used?

I've removed frozen and broken high tensile bolts out of my engine block on a couple of occasions. Either your tools or technique are faulty

The tightness is either from threadlock, and/or aluminium corrosion.

Maybe you need to drill it out close to the diameter, but this is very risky, as the drill will be ecstatic to make it's way into the softer metal. If you drill a larger diameter, you can centrepunch and drill through to the alloy at 45degrees inside the large hole with a 3mm drill, do this once on either side of the large hole's diameter. You could then squirt some good WD40 in there? If you haven't completely drilled out the hex bolt, then the WD40 might sit in there. Leave it overnight and give the screw extractors another go. Depending on the diameter you might have to use the centrepunch to "shock start" the bolt to move.

Otherwise try zapping the bolt with some oxy/acetylene torch, being careful not to melt the Alloy bit.

Getting good quality extractors just has to work.

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don't you heat the area around the bolt??? the idea being that this expands and the bolt doesn't, so you can just unwind it. I've done this often enough.

I'll try using a punch tomorrow, sounds like it could work. Failing that I'll have to take it to the farm and use the MIG to puta bolt head on it. Thanks for the advice, I'll let you know how it goes.

Of course that's better, try that too, but I don't like his chances in alloy. We don't have a lot of information. It's a shame that we don't have a photo to work from.

This man needs a bit of a miracle, especially if he doesn't have larger ezi-outs. But the mig and bolt trick is a great idea too.

I'd send a photo, but then you'd all realise the bolt isn't in a Datsun, its in the gearbox of a moto...sh*t, did I just let the cat out of the bag?

I'll try and get a photo up...might not be till tomorrow

Another trick Iv'e learnt over the years is before you try to undo bolts and screws that look a bit iffy I always try to tighten them a little first ....It breaks the seal that's been formed from years of neglect.... It works 95% of the time ,also good for old brake bleed nipples (oh how many I snapped before learning this trick).

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This still wouldn't have helped, coz someone else had already stuffed the hex bit

Aha, one of those bolts I had the same problem a couple of months ago in a Katana (the one that beat me) I ended up cracking the case trying to get it out .So I ended up buying another moto.