Sheared bolt removal + replacement - M5 or M6?

Jamey

Arrived at work this morning with the bike making a funny noise. Checked it over and noticed the rack and mudguard fixings on the left side were flapping about at the bottom.

I figured the bolt must have worked loose so I took another bolt from one of the bottle cage mounts to replace it with but it wouldn't screw in.

turns out the old bolt didn't work loose, the head sheared off. Pretty cleanly as well, there's nothing sticking out to get any purchase on with pliers at the side of the drop-out facing outwards.

I didn't check the other side but I'm praying there's some bolt protrusion on the other side of the drop-out so that I can use pliers to slowly unscrew it enough for it to protrude on the other side and finish the job but if that's not the case then I'll need to know how to remove it, so two questions...

1) How do you remove a sheared bolt when there's nothing to get purchase on? Can I glue something thin and twist-able onto it, perhaps? Will super glue work for metal-to-metal or would I need something else? I don't really want to drill it out if I can help it. Never done it before and don't know how to do it.

2) What size bolts are they? M5 or M6? The thread is the same as normal bottle cage mounts so that's M5 isn't it? I was planning to order some replacements from here.

maddog 2

drill a small hole through the centre and then screw in a bolt extractor. They tighten anti-clockwise so as they gain purchase they try to undo the original bolt



they are M5 bolts

Jamey

I see... Bolt extractors must be pretty small then, to fit inside a small channel in the middle of an already-small bolt? That pic makes them look massive.

ex-pat scot

Most mudguard eyelets are "straight through" rather than closed.
This means you could drill them through.

1. lots of penetrating oil, to help the threads turn
2. drill with narrow drill bit
3. slowly drill into the snapped shank of the bolt
4. with a bit of luck, the bolt will start turning
5. if bolt doesn't start turning, then by the time you've drilled the heart of it out there won't be much left- see if you can prise this out
6. if all else has failed- use a "p" clip instead for the mudguard

proto

If you go the 'drill through' route, try and find a left hand drill. Sometimes the mere pressure of the drill bit is enough to unscrew the remains of the bolt.

maddog 2

Jamey wrote:

That pic makes them look massive.

If you move away from the monitor ... 8)

the drill idea is worth trying first. And if the drill fits inside the frame dropouts you could drill from the inside, that way a clockwise drill bit will try to undo the stuck bolt.

Wamas

maddog 2 wrote:

If you move away from the monitor ... 8)

Reminds me of a Father Ted episode.

Now concentrate this time, Dougal. These
[he points to some plastic cows on the table] are very small;
those [pointing at some cows out of the window] are far away...

Jamey

Cheers for the help everyone.

For future reference, would an electric drill be powerful enough to use with a left-handed drill bit or do you need a proper mains-powered drill?

keef66

I'm sure any half decent battery powered drill would be OK, you'll be using a small diameter drill bit so it's not asking much of it.

I wouldn't worry about the left handed drill bit, a normal one will screw it straight out the other side if the threads loosen as you drill it out.

+1 for plenty of oil

Jamey

Yeah, I'll try a normal drill bit for this one, I was just wondering if it's worth having a small left-handed bit in my toolbox for any similar occurrences in future. Might invest in one.

Oh, also... Is there any standardisation to the colours of drill bits? I think my set has black ones and silver ones and some of the sizes are the same... I assume some are for drilling wood and others are a bit tougher but which is which?

stigofthedump

I think you will find left handed drill bits in the same section as Long weights and striped paint in the hardware store.

Drill bits are designed for different applications. Black ones are generally high speed steel for drilling metal, Masonary bits have a tungsten carbide tip which is braized in and looks like a chunk of something across the top, wood bits often have a small point and look quite flat. The wrong bit will become blunt long before to can drill your hole. Choose wisely.

Monty Dog

If you have a short-section of the screw protruding on the other side, you might be able to cut a slot with a junior hacksaw which will give enough purchase for a small screwdriver. If you try drilling, first use a hammer and centre punch in the middle of the screw otherwise the drill will wander all over the place. Best if you can clamp the frame and use a drill-press to keep the drill in the centre.

Jamey

Job done but what a ridiculous faff it was.

I got home, showered and went to work on the bike straight away. First up, needle-nose pliers to try to grab onto the section protruding on the other side of the drop-out.

No joy, not going to happen so immediately grab the drill and decide to start with a 1.5mm bit.

Twenty minutes later and I'm a grand total of about 1mm deep into the bolt so I figured I must be using the wrong type of drill bit as it's going to take me all night at this rate. Switch to a bit from a different set and it's equally bad at tunnelling into the bolt plus it snaps after a few minutes. Great.

At this point I thought maybe a larger bit might cause the bolt to turn just by the sheer rotating action so go for a 2mm bit. Straight away the bolt turns a tiny bit (about a quarter of a turn) and then stops again. But for some reason this bit is working and after a few minutes I've more than tripled the depth of the hole into the bolt. It's from exactly the same set as the original bit I tried so God knows why one worked and the other didn't but by this point I'm not complaining.

However, despite the depth of the hole, the bolt is still refusing to turn with the drill so I begin to think there might be something stopping it from turning forwards (through to the other side of the drop-out) and decide to try getting it to turn backwards (anti-clockwise).

I switched the drill into reverse and tried that but predictably without a left-hand drill bit it doesn't work. So I find a hex key that will just fit into the hole and try that.

Eureka!

Bolt comes out and I make a mental note to buy a (good quality HSS) 2mm left-hand bit for the future.

So now I decide to fix the rack and mudguards back on for today's commute. I've ordered replacement M5 bolts but they won't arrive until sometime over Easter so I decide to use a couple of bottle cage bolts, since they'll hold fine for one day.

I've got a cage mount underneath my down tube so decide it's best to take from there but notice that while they're both the same thread size, one has a slightly smaller hex fitting on the head than the other one.

No worries, I think, and go ahead. Normal hex one fits fine and so does smaller hex one, until I get to the torquing bit and suddenly I get that horrible feeling in my stomach as I tighten, then suddenly it goes soft and I realise I've rounded the head.

B*ll*cks.

Grab some pliers and try to undo it. Didn't think I'd managed to get it that tight before it rounded but obviously I'm wrong as the pliers are having no joy. Try mole grips but it's a rounded head and there's not enough sticking out for them to get a tight grip.

Remember that somebody said you can hammer a slightly oversize torx key into a rounded hex hole but the only torx key I have is way too large. So I try hammering in a slightly oversize hex key instead (an old one I don't care about, obviously) but again no joy.

Desperate (it's now about 11pm) I return to the pliers and giving it all the force I can muster I manage to get a quarter turn. On the verge of bruising my palms (can you even do that?) I force two more small turns and then the slightly oversize hex key can get just enough purchase to force another whole turn, after which I can get it to move with just my fingers.

Having learnt another lesson I now take a proper bolt from one of the bottle cages and use that instead.

Rack and mudguards back in action, time to refit the rear wheel.

Predictably, even though the brake arms were centred before removing the wheel they've now decided to rub on one side so I grab a screwdriver and sort that out. Now the rear brakes feel nice and tight... Tighter than the front... So I figure "in for a penny, in for a pound" and tighten / centre the front ones too, which fortunately goes smoothly.

Clear the multitude of tools away and at around midnight I finally go to get a well-earned kebab for dinner.

Everything held together on this morning's ride so as long as tonight is fine I'm home free.

Thanks everyone for the help.

iPete

Thanks for the detailed explanation, just purchased some second hand disc wheels to find a headless bolt still in one of the threads :roll:

Will do the same as you and be taking a drill to it later! Was also thinking that the extractor bits look waaay to big to fit inside a M5 bolt! Sound like you didn't need them though, fingers crossed...

blackhands

Bolts don't normally just break - there must be an underlying reason. I Jamey's case I suspect that it was tight in the frame which may need the threads cleaned out with a tap. On my touring bike I use nuts on the end of a slightly long bolt - 1/2 nuts to make sure they clear the chain,