HELP!8mm self extracting crankarm attach bolt

I have not tried this, except with PoP Rivets.

CAERFULLY, with an 8mm drill bit, drill out the head of the bolt. The head should fall off when you reach the shaft of the bolt.

Then use a normal crank extractor to remove the crank arm. The remaining shaft of the bolt should then be accessable with some locking pliers, ViceGrips.

Depending on how rounded out it is you may be able to get it with a Torx socket.

I've gotten some seriously screwed up allen head bolts out this way. You'll need a Torx socket that is just able to fit the hex recess (the largest size you can knock in with a few sharp raps of a hammer) and use an impact driver if you have one. The tapping in of the socket will unload the strain on the threads while turning it and usually it comes right out.

If it doesn't work you can still drill it out, but if it does you're home free !

+1 on the Torx socket way.

I used this method sucessfully to unscrew 3 stripped hex head screw from a set of cleats. The bolts had rusted and that caused me to strip the head in the first place.

A liberal blast of WD40 together with the Torx socket helped me to finally unscrew the cleats.