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I'm trying to remove the transmission casing on my belt drive scooter. All of the bolts have tiny 8mm heads, and are very cheap and soft - cheap Chinese manufacture - and one was already slightly rounded, from assembly as a new bike.

I have now sprayed Q10 penetrating oil, and waited a few minutes before tapping lightly with a hammer, on the front and sides of the bolt head. What is really worrying is that when I tap the side of the bolt head, it moves as much as 0.7mm, in any direction. The head is too close to a casing piece to get any good grip with a vice grip.

What can I do here? There is no room to cut a groove with a hacksaw, but maybe if I get a thin enough grinding disk on an angle grinder I can cut a groove, or maybe grind the head flat enough for a vice grip to hold.

What can I do?

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A picture might help us make a more specific recommendation. – Bob Cross Jan 19 '13 at 15:56
Do you have a Dremel that you could slot it with? (Or a friend with a Dremel?) – Doresoom Jan 19 '13 at 21:46
I found a miniscule angle to get a hacksaw in and cut a slot in the bolt head. Then I hammered a screwdriver into that and shocked it left and right with locking pliers. – ProfK Jan 20 '13 at 6:13

You can try heating it with a torch to loosen it. You could also get a reverse-direction drill bit, and drill down into the bolt; the heat will help the reverse bit to unscrew it, and if not then you can easily get the remainder of the bolt out by stepping up bit sizes.

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The reverse direction drill bit might be perfect for this application. – Bob Cross Mar 4 '13 at 22:13

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