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I need to take out my rear shock but one of the 2 allen bolts that is holding it (the upper one) has been rounded.

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I've been told about various ways that such a bolt can be taken out including:

  • hammer a torx in and unscrew
  • drill a line using a dremel and unscrew with a screwdriver (I don't think the latter will work, the bold is too tight)
  • hammer a larger allen key in and unscrew
  • drill the hell out of the bolt (I don't want this because I'm afraid I'll damage other parts of the link (bushings etc)

What do you propose for this case?

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  • Yep, screw/bolt extractor. Either that or drill it completely out. You might be able to hammer in a Torx, but there may or may not be a size of Torx that will work. (Note that you need a bolt extractor with good threads near the tip -- some are long and slender and won't get in deep enough to grab.) – Daniel R Hicks Oct 15 '12 at 15:10
  • As well as what has been already said, if it has corroded in place, drilling through the middle can loosen it due to the heat generated. It's a good start for using a drill extractor. Also, if you have a screwdriver that fits the mangled hole well enough that can work. – DanS Oct 16 '12 at 8:06
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    Another option is a left-handed drill. Drill straight through the bolt with it (the drill set to reverse) and often, after you've gone a half-inch or so, the bolt will begin to unthread. Failing that, use a larger drill bit to drill the head off, then hope you can somehow grasp the body of the bolt once things are disassembled. – Daniel R Hicks Oct 16 '12 at 11:00
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I'd try a screw remover like these. You'll need to either get a set or bring the bolt in to make sure you get the right size (Sears sells their own version that's supposed to be excellent). The good ones have a left-hand thread and a small cutting head to bite into the bead of the bolt; this looks like a really good candidate for a screw remover since the head is nice and large and has enough material for the remover to be able to grab.

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  • Thanks. What if I don't want to purchase a screw remover? (I've already spent 20e on the replacement bolt). What would be the next best option? – cherouvim Oct 16 '12 at 8:33
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    @cherouvim -- In the US many hardware stores carry the individual extractors for $3 to $10, depending on size. Take the replacement bolt with you and you can pick the extractor that matches it well, vs having to buy a whole set. – Daniel R Hicks Oct 16 '12 at 10:57
  • So I got an extractors kit like the one above. None fits. One doesn't fit in the whole at all and the other is too small. What should I do? For the first I could enlarge the bolt whole a bit so it fits. For the second extractor I could cut it in half so I start using it from it's larger diameter part. What do you suggest? – cherouvim Oct 17 '12 at 5:26
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    Are they double-sided? Often one side is used to drill in to the bolt, and the other pulls the bolt out. You may need to drill the hole out slightly for the tip of the extractor to fit in; be careful not to drill too large a hole (start with a hole that the tip barely fits in); remember that the idea is that the left-handed thread cuts into the hole as the extractor spins in. – lawndartcatcher Oct 17 '12 at 12:29
  • Thanks. Will slightly drill the hole so the larger extractor fits. – cherouvim Oct 18 '12 at 7:07
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There are special screw extrators for this purpose. Every well equipped car or bike repair should have such, maybe you will also find them in a DIY store. The only question is, if it is worth the money to buy an own one if you have only one screw to remove.

Maybe also this link will help.

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    Screw extractors are the type of thing that once you own them you'll wonder how you ever lived without them. Just make sure you invest in a good set; I've broken lots of cheap ones off. – lawndartcatcher Oct 15 '12 at 13:12
  • That's as good point ;-) – Benedikt Bauer Oct 15 '12 at 13:14
  • Make sure you have a set of good drill bits to make the starter hole for the extractor too. – Dan Is Fiddling By Firelight Oct 15 '12 at 15:59
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    Shouldn't need to drill a hole if the extractor fits the hex socket well. – Daniel R Hicks Oct 15 '12 at 17:49
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I'll post the results as an answer although I've already accepted a solution.

The bolt extractor did not help me. That's because the bolt was so tight on its nut. I think that the bolt had made a bond with the nut. It was impossible to unscrew it. Initially any attempt to hook the extractor resulted in more alumenium material from the bolt to be extracted. Then I drilled a smaller whole in the center of the bolt and tried with a smaller extractor. It broke.

I also drilled a torx pattern on the bolt's head but the torx also melted the aluminium of the bolt.

I ended up drilling the hell out of the bolts back end where it binds to the nut. When I've drilled a complete circle around the threads of the bolt and nut, I could hammer the bolt out.

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  • I find it hard to believe that the bolt would have been aluminum. I can't think of a worse material to use to secure a shock. – Daniel R Hicks Oct 25 '12 at 12:00
  • I'm not an expert on materials but I feel that the bolt was very soft. No matter what tool I used (high or low quality) it would scrape material out of the bolt's head very easily. The replacement bolt I got from the company looks sharper and of different hardness and colour. – cherouvim Oct 25 '12 at 12:04
  • Wow! What a nightmare. Maybe it was a really soft steel that corroded on to the nut? – lawndartcatcher Oct 30 '12 at 14:42
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    Yes. It sucked. But now everything works smoothly with the new bolt in place. – cherouvim Oct 30 '12 at 15:40
  • So this question is now 6 years old. Would you be able to add more info about how its going? Did other bolts round-off with age? Did the new bolt rust and seize like the first one? – Criggie♦ May 27 '17 at 21:52
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Yes, normally if a bolt get stuck there are 2 possibilities. 1) in shops often they have bolt extractors; they rip firmly on the bolt and then should be possible to unscrew it. 2)another solution I have found to remove bolts has been using glue. So put the bike of its side, so that you can drop the glue in and stuck the hex key in too, to bond. Leave it to rest and if the glue is strong enough try unscrewing it, to remove it. It worked for me a few times.

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Cut a slit/slot in it and pull it out with flat-head screw driver.

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    Hi, welcome to bicycles. Note that the question already suggests this approach, so if you're going to recommend it you need to provide some more details and practical suggestions to make it work. Just repeating something that's already in the question or another answer doesn't make for a good answer; please read How to Answer. – DavidW Jul 30 '20 at 20:03
  • This is a valid answer that hasn't been listed in answers though did get a mention in the question initially. Consider using edit to expand this - a one-line answer generally needs details. I also changed "philips" to "flat-head" because that seemed like a simple substitution error. You might also add info about how to cut the slot, ie what tools to use (hacksaw, dremel,.....), how to avoid damage to the surrounding frame. It can also help to read the tour to learn how Stackexchange is organised. – Criggie♦ Jul 30 '20 at 20:46

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