ideas for removing stripped bolt

Does anyone have any ideas for removing a rounded-off crank bolt? The 9/16 socket wrench just spins around it, and the 1/2 socket doesn’t fit, but I really need to get this crank off!
Ok, all you smart engineer-types, impress me with your ingenuity! BTW, I trying to get the crank off of junked bike, so I can use it on my uni, so it doesn’ t matter if I damage the rest of the bike in the process, I just want the crank.


Re: ideas for removing stripped bolt

Get a bolt extractor of the right size.

Or, if you’re low on time/cash, carefully drill out the center of the bolt with progressively larger drill bits. Use pliers/vice grips to mangle and remove the bolt.

The easiest way is to drill it out. Start dead centre on the head, and drill straight along the axis of the bolt, with a drill bit the same thickness as the threaded part. The head will fall off, and you can pull the crank against the bit left behind. If you need to, you can saw a slot in the leftover bit and take it out with a screwdriver.

It’s most likely a 14mm bolt or nut. A 9/16 inch socket is going to be slightly too big. 9/16 inch is 14.3 mm which may be why it is slipping. Find a good quality 14 mm socket and you may have better luck. Better quality sockets will fit better and be less likely to slip.

There are also special bolt cracker tools. But you probably don’t want to go there yet, and I’m not sure if you could get the bolt cracker inside the recess of the crank.

Drilling is also going to be difficult. The bolt and the spindle are probably hardened steel which will be very difficult to drill.

Thanks for that. I’m going to our island’s one hardware store during my lunch break to see if they’ve got a bolt-extractor or a 14mm socket.

Is it a bolt or a nut? One most cranks, it’s a nut.

A crude engineering solution which sometimes works is to get an old socket which is a little bit too small and hammer it on.

Another would be to cut a slot and use a BB screwdriver.

(BB is the universal standard size: Bloody Big.)

This works even better if you heat the socket with a torch first. When it cools it really grabs on.

If it is a nut it can be cut with a small grinder. Tedious but effective.

Cyberbellum’s bolt extractor theory will only work if you can drill a hole in the center of the bolt and you would need a healthy bolt extractor to make sure it doesn’t break. Is it a crank NUT or a crank BOLT? The bolt extractor won’t work with a nut anyway.

Get a six point 14mm socket if you can find one rather than a twelve point which is more likely. Heat the AXLE slightly with a propane torch if it is a bolt. Heat the NUT only, if it is a nut. Then loosen.

Greg, you must be thinking of a screw extractor which I agree won’t work on either. A bolt extractor is a cap with reverse fluted cutters on the inside that will work on either a nut or a bolt IF it can fit into the crank. It screws over a rounded nub and grabs on from the outside. [A screw extractor is a tapered rod with reverse fluted cutters on the outside. You drill the screw and then fit the extractor into the hole to grab what’s left and unscrew it. If the crank bolt is really in there the scew extractor will probably just snap off.]

Enthusiastically agree about a six-point socket. They’re hard to find but they really do work better on stubborn parts.

I didn’t recommend heating because the crank is still on over the taper. It would be hard to heat the steel without damaging the aluminum. In any other setting the heating trick almost always works. Pre-chilling the parts in a freezer makes it work even bettter.

When all else fails use a die grinder carefully. Grinding flats so that you can lock a pair of vice grips on is a winning strategy that I’ve used twice so far. Very tedious and time consuming, but whenever a job involves surgically mangling something then vice grips and die grinders are things of beauty.

It’s a bit late if the head has already rounded, but a flank drive is even better than a 6 point.

What’s a flank drive?