Rounded allen bolt - tips needed!

^ This. Cut the screw at the slot in the seat clamp. If you're lucky once the pre- load has been relieved from the screw you can wiggle the threaded part out and will only have to replace the screw.

I am a but surprised by this as you used a torque wrench .. Assuming that's an original Thomson screw they claim to use 12.8 grade screws and recommend an install torque of 2.8Nm for the collar so there should be plenty of safety margin .. around a factor of 4 I think. Is the drive bit you are using with the torque wrench nice a 'sharp' tight fit and not rounded or damaged so it can 'slip'? Obvious question is calibration of the wrench ..

I'll give it a go with a hacksaw. Oswald, I haven't always used a torque wrench so I guess it was already a bit dodgy. Just checking, are you both suggesting going via the slot? Will have to check but I think it's quite tight. I know some people cut across the head to make it accessible to a screwdriver, but this may also be tricky to do.

A torque wrench doesn't stop you inserting the allen key incorrectly or prevent the use of crap allen keys - it just makes it less likely you'll crush the post or break the clamp.

^^ Yes. Cut at the slot. It is tight but doable .. check the blade width against the slot and maybe even get a junior hacksaw if the blade is too thick. You'll only need to get about 3/4+ of the way though and the screw will snap as the tension exceeds the material yield. Leaving you with the head loose and the body threaded into the clamp not under tension. You should then be able to fiddle with the screwed part left in the clamp afterwards to remove it. Cutting a slot in the head of the screw because it's recessed will wreck the clamp totally.

its also likely that the bolt is harder than the clamp and so you could quite easily end up damaging the clamp if trying to drill out the bolt. another vote for cutting the bolt

Use a T25 torx bit (or a T30 if it is well rounded)
Tap the bit in with a hammer so it is tight in the bolt's socket and use a bit driver to undo it.

I'll dremel the bolt's shank for 2 cans of beer. E11.

Slot is too close together to fit any kind of blade through. So maybe I've tightened it too far despite use of a torque wrench, or maybe the outer diameter of the tube is slightly less than usual? Anyway need to look at other options. Already tried using a torx bit, unsuccessful - maybe need to hammer it harder but got worried about damaging frame.. 57Hawkes, you're a bit of a trek from me & don't have much free time over next few days, but will bear your kind offer in mind if still having problems.. Thanks for all the tips so far.

The only option I think, is to get a drill. I'm sure that Thomson uses an M5 screw. So get a 4mm drill bit and drill the screw from the side where the allen key goes. What the aim is here is to take the cap head off of the screw. The standard socket size across flats for an M5 screw is 4mm so the drill should fit into the cap and centralise. Now the root diameter of an M5 is near enough 4mm. So once you drill thought the cap head and into the screw the screw should fail and the cap come off. You've then released the tension the same as cutting at the slot.

The seat collar is the right size for the frame? Seems strange you've closed the gap so tight and I can't see how you've tightened it too far with a torque wrench unless you set the wrench wrong .. or you ignored the click?

Had a bit of a go with a drill this afternoon but it's taking ages to get anywhere. Any particular kind of drill bit I should be using? Worth starting with a smaller one?

The screw grade that Thomson claim to use is really hard. I don't know what you're doing so ignore any comment that's obvious!

Drill speed .. You need to go slow or the drill will spin, overheat and go blunt.
Drill feed (how much you press down) .. You need to be aggressive to start the drill cutting then back off and let the drill do the work.
Lube .. Use some oil. Ideally it would be cutting fluid but chain lube or anything that keeps the cutting action cool.
Drill .. Ideally you want a Cobalt drill. You can use HSS but it will blunt quickly so you'll need to change drills. Also you want the shortest drill length possible so a stub drill is better. The longer the length of drill extending from the chuck the more it can vibrate. Vibration leads to the cutting edges going blunt.

Using a smaller diameter pilot drill to start with will allow a higher drill speed and when you move up to the 4mm it has less material to remove but you'll have to be more carefully to avoid drill breakage. I hope that gives you some options ..

Thanks for taking the time to explain this stuff, I appreciate it. I'll see how it goes.

I have used a hex wrench that fits the hole, just, and then hammered it into it lightly to get a secure fit, then unscrewed it ... This happened with a recessed nut for my front brake - and bearing careful as the fork is carbon..

If you have a rounded counter-sunk capscrew there are two tricks not yet mentioned:

a) prep your hex-key. Often the ends are not square and the corners not sharp; grind them so.

b) use an impact-driver - the kind you hit with a hammer is best as you can adjust the amount of "pre-twist" you apply, and the amount of hit you give. If it needs a big hit, support the other end of the bolt if you can.

Removing a stripped hex screw - YouTube

Insightful and funny

+1 screw extractors. Great on large bolts (6mm plus) but near hopeless on smaller ones. My lbs got a stripped hex out of a vitus by soldering a long handle 4mm Allen key into the stripped hole. I've also seen this done successfully with a welding joint on stuck pedals into cranks you have to cut the bulk of the pedal off to leave a stub of the spindle, weld a steel bar onto it at 90 degrees and bosh, it's off. It's all about leverage innit!!

And heat. I got some sheared bolts out of the engine block on the GF's Ginetta by welding nuts onto them. Then the engine seized, but that's another story...

Bump on this as I have rounded out one of the pinch bolts in a shimano chainset.

I have tried all techniques here and goodness knows what alloy the bolt is as it just rounded more and more.

The araldite trick nearly worked, but not enough.

Today in a last ditch attempt before cutting the bolt and therefore ruining the crank I will be bonding a larger allan key filed to fit the hole in place with milliput - an epoxy resin.

I'm hoping the stiff nature of the putty will take the rotation force better than the araldite.

I'll report in the next few days

@nomoreknees, is it a crankbolt? I drilled one out recently, I think I used smaller than the outside size of the thread, e.g. if it's 10mm (I forget the size) I used a 8mm.

Hollowtech pinch bolt?

Should only be 12nm or so IIRC. So corroded in place? They are threadlocked from the factory...tried heat I guess?

(Ignore the red circle)

Hi Howard, yes hollotech2 pinch bolt.

The crank has been in place for 5 years or so :D I only realised that the BB had had it when I washed my bike the other day and the loosened the road grime that had kept it aligned.

This is my do everything bike - tens of thousands of miles commuting and off road etc etc.
I think you're right - The bolt must be corroded in place and wedged with flith.

Tried heat, imperial Allan key (just rounded the metal more), torx head hammered in place (just rounded more) and araldite imperial Allan key.
Managed a little turn then the glue cracked.

No luck with an easy out either? Dang.

TLDR

Easy out is my very last resort.

I'm hoping the milliput today will work (won't know until it sets tomorrow)

Hi shipright, no a pinch bolt from the hollotech2 series