I have sheared off the head of a bolt on my bike - it’s the bolt above the rear dropout for mounting a rack or a mudguard. This is quite a small bolt, I’d guess 2-3 mm dia, and it’s come clean off with nothing left to grab hold of.
I understand you can drill it out - How do I go about doing this? I have a couple of hand held power drills, but I don’t have a good vice or anything like that to clamp the bike. Is it a simple job just to freehand it with the bike resting up against a wall?
Will drilling it out bollox the threads within the frame? I’m wondering how easy it would be to cut new threads on what is a rather small mounting hole.
Did you shear it off trying to remove it, or trying to screw it in too tightly? IOW, are the threads frozen?
Head to a hardware store or tool shop and look for a screw extractor kit. These vary in design somewhat, but the important part is that you drill a small hole down the center of the broken screw and then insert the extractor, which is designed to bite into thew screw when turned counterclockwise, which is the direction that will tend to loosen the screw. Some extractors require you to pre-drill the hole, others have a left-handed drill bit incorporated into their tip.
Be careful about turning the extractor too firmly; it’s usually made of very hard material, and if it breaks off inside the screw, you may not be able to drill through it, and then you’ll be…screwed. If it feels like it’s not going to come loose, remove the extractor and go for drilling/tapping instead. Check the screw from the eyelet on the other side of the frame to see what the threads are for your busted screw (I’m guessing M4, M5, or M6? make sure you also get the thread pitch right). Go back to that hardware store, buy a tap and the correct-sized drill bit (if the tap doesn’t say on its side what drill to use, google “*** tap drill,” where *** is your tap size). Drill out the screw, and run the tap in as straight as you can. If you’re lucky, the tap will “find” the original threads and just cut away the undrilled remnants of the busted screw.
Thanks **Machine Elf **that’s v helpful. I sheared it trying to remove it - the bike’s a tricross that I’ve been commuting on through a harsh UK winter; it’s been ridden hard and put away wet and I was performing some long over due tlc (or trying to). I have the screw from the other side so should be Ok getting the right tap, bit etc.
I guess I didn’t really cover this. You can freehand it, but first you’ll want to use a center punch+hammer to make a small divot in the center of the broken screw; this will assure your drill bit doesn’t wander when you’re just starting the hole. The other thing that will minimize wandering of the bit is if you start with a very small drill bit (say, 1/16", about 1.5mm) that will have an easier time staying in your punched divot. Once you’ve got that small hole drilled, you can graduate to the appropriately sized bit for the tap you’ll be using. If you use that small a bit, spin it fast and make sure you’re pushing as straight as you can; if the bit breaks off in the hole, you are probably screwed again.
If the threads you end up with at the end of this project don’t hold the screw very well, you can always drill them out altogether and just use a nut on the free end of the bolt.
if the bolt goes through the dropout and protrudes then you might grab the front end of the bolt with a locking pliers and rotate it (in the same direction to tighten) and bring it all the way through.
I had a bolt break off the alternator mount in my car. I took it to a mechanic who I thought would drill it out or have a screw remover described above. His approach, due to the fact that the back of the bolt was the coolant jacket in the engine, was to use a hammer to turn the bolt out. It worked and didn’t take too long.
I realize it is small, but you may be able to do this. Use a hammer and nail punch (or a nail) on the edge of the exposed bolt to turn the remains. Once enough of it is exposed, try to grab it with pliers and turn it out.
If you bugger the threads you can always ream it out and attach a longer bolt with a nut on the other side of the hole.
Thanks all. I’m reasonably sure that there’s no hole on the other side for the screw to go all the way through. It’s just a threaded hole on the exterior of the seat stay.
It sounds like the bolt might be rusted in place, so it might help to apply a little WD-40 to the bolt. If possible, lay the bike on its side so gravity will pull the liquid down through the threads. Sometimes it helps to tap the bolt (or bike frame) as well. Good luck!