Damaged hex head

[def]

During some routine maintenance I noticed that my rear derailleur hanger was loose.
Both the bolts have hex heads but one was damaged and I couldn't get a hex key into
it.

Any tips for repairing a hex head? The damage appears to mainly be around the top
where it looks like chain has rubbed against it.

I'd like to get new bolts but a mate of mine tried that recently and could't get any
from his LBS.

def

[al]

Might need an "easy out" kit to remove it if it is really bad.

[josephk86]

You could try clamping the bolt head with a pair of Vice Grips nice and tight? Usually does the trick.

[revinR1]

Dont know how this will work in that area but you could try either of the following
1. Some how tap a flat blade screw driver into where the hex head goes and undo carefully.Note you`ll need a slightly larger driver and you`ll be using the outer edges to get a grip to undo
2. Is it possiable to get a hack saw in and place a small cut/groove into the head and undo using a flat blade driver.

If you go to your local nut and bolt place they will be able to match the threads to replace you bolts etc

[queequeg]

I had the same issue last week with two torx bolts on my disc rotors.

I ended up using a chefs blow torch to heat the bolts, then some vise grips to get it moving. The thread lock didn't help, but once I broke the inital bond the bolts unscrewed with my fingers.

[def]

Some good suggestions there - especially the screwdriver one from revinR1.

Some of the others won't work as the top of the bolt is flush - no protrusion to grip or saw a groove into.
It's also a carbon frame so I'm reluctant to go with a flame thrower!

I think I'll try hard to get new bolts.

Cheers All.

[Saturnstarzz]

Get a small nail punch and a rubber mallet and give the ends of the bolt ( In the frame) a little tap might move them enough to get a screw driver in the head and to give the thread some bite.

[toolonglegs]

Use a torx head socket which is a bit big to fit into the allen head, "press it in" with a hammer. Works well for taking out damaged allen bolts, don't know if I would do it for reinstalling them though as it will make it hard to get out next time. Use a thread lock liquid too.

[ctguru]

I have had success using a slightlysmaller size (maybe imperial) and using lapping paste to help the hex key grip

[drubie]

If all that fails, drill the head out (carefully). You can usually unscrew what is left with your fingers or pliers once the replaceable hanger is out of the way.

[laterstarter]

I have run into this problem with a seat post that requires high torque to keep the seat in place. The female hex part of the bolt had rounded out. Bought an "Easy Out" from Bunnings; drilled a hole into the bolt in the middle of the head and the applied the Easy Out. Bolt came out easily.
To avoid a repetition, I bought a stack of stainless steel bolts from a bolt supply shop in Virginia. Cost me about $10-15 for about 30 bolts of various sizes. (were about $2 each from a bike shop) The bolt shops seem to be Aus wide - (I googled them). The SS bolts seem to be much more resilient to burring than titanium or mlld steel bolts.

[Ropecharmer]

I would usually grind a cheap Allen Key to fit the bolt, tap it in with a hammer and away you go.

If the head is completely shot, however, an 'Industrial Supplies' mob will be able to sell you a left-handed drill bit that will unscrew the bolt as it bites into the head. Might cost $12, but it could save you a world of pain.

There's also professional bolt removal and thread repair services available, if all else fails.