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Rounding out an allen head/unbrako bolt - what to do?

Discussion in 'Technical and Troubleshooting Torque' started by robsalvv, Nov 9, 2010.

  1. Help me folks, I've almost rounded out the brake pad retaining bolt on one of the front calipers. The previous nong (me) used too much thread locker.

    What are my bolt removal options??
  2. Depends on the bolt itself, if you drill the head will there be enough exposed bolt left to get a grip on?

    If not, try cutting a slot into it & using a flat head bit in an impact driver. Some heat will free up the threadlock, too.

  3. It's a flush mounted/counter sunk bolt unfortunately.
  4. I've done sillier things ... sometimes.
    I'd ](*,) and :censored: then :cry: and probably call in a professional, with a drill press and easy-outs, and helicoils if that doesn't work. You really need a workshop, and someone who knows what he's doing. Or a new calliper.
    8-[ ... sorry...
  5. First off, you need to destroy the thread-lock. Heat will do that. Get a bit of steel (copper or brass are better but you're less likely to have any), heat (on the stove if you've no blowtorch) and apply to the bolt head for a while. You can reheat a few tmes if necessary. If you've an old or cheap allen key you're prepared to sacrifice, that would be good as it will fit into the head and give you more heat transfer surface.

    Having got the bolt up to maybe 120-150 degrees, that should be enough to kill the threadlock. Now for turning the thing.

    Least drastic approach is to apply a bit of valve grinding paste to the end of your hex key. It gives a better grip in dodgy sockets. Just don't forget to sterilise your tools afterwards so the paste doesn't make it into your engine next time you use them :D.

    If that doesn't work, have you an imperial sixed hex key slightly bigger than the correct metric one? If so, you might be able to hammer it in. Again, it may mean sacrificing the tool for the job. Sticking the hex key on the end of an impact driver will also help.

    Better yet, if you can borrow a compressor and a rattle gun, I've had good results with large, chewed up crosshead screws, so if you've managed to get a hex to grip at all I'd be quite hopeful.

    Failing getting a hex to fit in, can you knock it round with a centre punch? Again, I've had some success wth this in otherwise hopeless cases, mostly Phillips heads with only a smooth, conical depression remaining, so it's worth a shot.

    Finally, if you have/know someone who has a welder, try welding a bolt to the bolt head. It will take a fair bit of delicacy to avoid buggering up the caliper but the heating will be of benefit and it'll give you something to grip.

    After that, you're stuck with trying to drill it out or using a stud extractor. I'm not sure how well that'll work as, in my experience, a lot of socket head bolts appear to be hardened. Besides, I don't trust stud extractors and would regard them as very much a last resort. I'd be inclined to remove the caliper, take it to a proper engineering company and pay :shock: them to drill the thing out properly before I risked one TBH.
  6. Thanks Pat. I've got a blow torch. I've got metric and imperial allen keys... I will be giving those tricks a shot. There's no grinding paste in my place (a bit of grinding of teeth, but no paste), but that idea has a lot of merit. There's still some corner in the bolt so at this stage I'm hopeful... extractors will be a last ditched effort.

    KD, I'm not replacing the whole frigging caliper. lol. *spits on the ground, makes some ancient greek hand gestures and the italian devil horns to ward off a mozz*
  7. Thanks Pat. That 'Weld a bolt head on it' is actually a very good idea. I forgot about that one. Also worth noting, go through Pat's steps in the order he mentions them, from least invasive / forceful / desperate, towards ... 'It needed replacing anyway.'

    [edit] [grin]
    Well, you hope you don't have to replace the calliper.

    Did you ever see 'Capricorn One' back in the day? An astronaut tells a joke, to take his mind off what he's doing, which is very dangerous. The joke went something like ...

    This lady goes on holiday, and leaves her husband to watch the house, her elderly mother, and the family cat. So after a couple of days she rings up and says "Hello Dear. How's everything going?"
    The husband goes "Oh, yeah, you know. Could be better. I'm fine..."
    She goes "Ok, how's the cat?"
    "Honey ... your cat's dead."
    She can't believe it. "My cat's ... What do mean the cat's dead? She was fine. And how could you just throw that at me from left field like that? Don't you know anything? You break news to people like that slowly. On the first day, like, Fluffy was playing on the roof, and I think maybe she had a little fall, but I'm taking her to the vet, and on the next day, oh the vet says things are a little more serious but I'm sure she'll be fine, and on the third you say she seems to have stabilised now but she gave us a bad turn last night, and on the last day you break it very gently that the cat has passed on. Poor Fluffy."
    He's all contrite and "Sorry hon, I'll try and remember that, for if ever, you know."
    So she catches her breath and dries her eyes, then asks "How's Mum?"
    "Well she was playing on the roof ..."
  8. Just to highlight which bolt I'm talking about - I found this pic which is similar to my calipers.


    I've rounded the pad retaining bolt in the middle of the pic.
  9. You could also try heating it, then seeing if you can get a pair of vice grips onto the bolt between the calipers & undoing that way (assuming you can get access like in the pic)

    If the metal is soft enough, the vice grips will grip quite well.
  10. Good call MV. My calipers are similar to the ones depicted. I'd have to remove the caliper from the bike to get that kind of access... but it gives me another option.

    Much appreciated gents.
  11. You can often flog a slightly larger Torx bit in there when the allan key is rounded out but you will need to heat it first and you can spray the heated bolt with Rost off ice (any aerosol will do but the ice stuff is better) to shrink the bolt out of the housing, spray it on the thread end if you can get to it.
  12. I vote for:
    Buy a replacement bolt.
    Get a longish straight slightly oversized hex key, or cut a long handled one down to just the straight length.
    Belt the hey key into the bolt. Maybe chill the tip of the hex key first to shrink it.
    Heat the hex key as close to the bolt as possible without risking damage to the caliper (shield it), to melt the thread locker.
    Use a socket and breaker bar on the hex key to undo the bolt, so that you only apply rotational and axial force, avoiding twisting the hex key out of the bolt sideways.
    Throw the bolt and hex key away (probably still near welded together). They were well cheaper than a caliper.

    I don't trust Easy Outs and such either. Give me a good solid interference fit any time.
  13. Bloody hell, that dates you a bit. I was twelve when I went to the cinema to see that :grin:.
  14. Success!

    Heat and an over toleranced cheap 5mm allen key smashed into the retaining pin bolt head did the trick. Front wheel pads have been checked.

    Ok next question to you savvy crew, why would one pad be down to 1mm remaining material (now since swapped for an ok old pad I kept from a while back) and the other three pads be in the 2.5-2.8mm ball park?

    p.s. I haven't reused the pin. I was able to recover the pin from a spare caliper I picked up in junk box of ZX9 parts... just incase you were wondering.
  15. My guess is it was a friday arvo pad.
  16. Hmmm. I've seen sets with one thick pad, due to a sticky piston or slider pin, but I don't think I've come across the opposite. Unless you've got three (or whatever) seized pistons and one free one, it doesn't seem likely.

    Do you have a floating disc stuck over to one side on its bobbins?
  17. Might need to be pulled apart and serviced
  18. [grin] Thanks Pat - I was about 14. I just remember the joke, because it cracked me up.

    Glad you got it out Rob. Good news.

    One pad more worn, suggests to me that one piston on that pad is a little bit sticky. I would be on the lookout for signs that one piston is not retracting as well as the rest. From time to time when getting off the bike, put your hand near the disks and feel whether the one with the worn pad is a bit hotter than the other. Get a mate to hold the bike back and up on the side stand, with the front wheel just off the ground, and spin it, to see if it spins freely, or half of one calliper is binding slightly. Stop and check the temps (you can probably do this by touch, I think) of all the piston holders on the callipers - inside L outside L, inside R... is one hotter than the others? ...

    If you find one sticky pot, you may be able to push it out as far as you dare with the bake lever, then spray the whole area liberally with BrakeClean, and clean around it with a cotton bud, spray again and blow off with compressed air, then push it all the way in with a G-clamp, then reassemble. If that doesn't do it, you may have to strip and properly clean the calliper, and that I'm not going to instruct on because I don't know.
  19. My rear brake does that all the time. I have had it looked at, cleaned, serviced, asked the mechanics why, and have never received a satisfactory answer. It seems it just works that way.

    So if you find a reasonable answer, let me know Rob.
  20. Thinking about it, my K100 used to do that at the back. I always assumed the thick pad wasn't being pushed, but now kneedragon mentions it, there's no reason why it shouldn't be the worn pad failing to retract. Hadn't really occurred to me.