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I wanted to try a single ring up front so I tried to remove the bolt. I then failed to use the right size of Torx driver and rounded it. To get round this I drilled the head off the top, but couldn't get the tread part out. No worries about using it single ring, but I've realized that an inner chainring would be a good thing, given my current status of non-fitness. Can anyone help me with this situation?
Pictures? Not sure what you're getting at? Which bolt?
What you want is a stud extractor .....
Have you exposed the hollow core of the bolt, if so screw the reverse thread stud extractor into the bolt the wrong way from normal (left) and hope it comes out.
Use plenty of WD40 and allow to soak first for 20mins.
Good luck
Just use progressively bigger drill bits until you've got all the bolt out surely?
ask your friendly LBS??? i did the same to a stem bolt and my local shop Bikestyle managed to get it out without too much head shaking and sighing.... it was the day before i was off for a weekend to CyB so no pressure...
depends - some crank bolts go into a 'blind hole' where you don't have through access.
most stud extractors have a tapered start which won't 'bite' before the tool bottoms out.
Same with drilling out - it's ok but you can't get a thread cutter in afterwards to chase the threads for the next time you use it.
[url= http://www.recoilshop.net/thread-repair-kits-c-95.html?oscsid=23914edfdf53be5c41c2793b0edb29d0 ]Helicoil kit[/url] If its in Ally then drill the WHOLE of the remnant out and insert a Helicoil thread repair, this depends on size of the original.
If it's in hardened steel, drill and tap out to a slightly bigger size, but to really advise need pics of the offending beastie 🙂
Sounds like a perfect job for a shaped charge... 🙂
Rachel
http://www.screwfix.com/p/screw-extractor-set/18643
You will need to use a bit of judgement on hole size and which extractor to use. Grind off the end of the extractor so it fits right, but not too much or it just wont lead in and bight. Dont go big on the hole or it can break up and muller the hole. Dont use too small or it can snap extractor if bolt is in tight and then it requires spark erosion! Good if you can also buy a tap wrench (the other kind)to drive it squarely.
lets see how much is left first.
If you can get a grabbit bit in, use that. If too deep a hole then drill out very carefully with a smaller bit, then clear remains with a tap and die kit
The problem bolt is one of the inner ring bolts.
Got ya.... sort of know where you are coming from now.
I'm [u][b]assuming[/b][/u] that this is into the crank spider ergo a blind hole.. it will be ally (hardened but still soft as butter in engineering terms). And it's gonna be M4 or m5 so its small.
You NEED to find a bench drill as any attempt with a hand drill will end in tears, the spider needs to be locked up so it can't move as does the drill even if you are drilling a pilot hole in the bolt for the extractor, precision is the key here.
Issue I have had with extractors particularly at this size is they are very, very brittle and any lateral play and you will snap it. Bitter experience would lead me to reccomend overboring it and popping a helicoil insert in.
Personally, if you haven't got the kit then hand the job over to someone who has, but also weigh up the economics... is it going to be cheaper to just replace the crank and spider than pay someone to do it.
One last trick in the arsenal... if you haven't got the gear is have you tried heating the spider, prior to trying to turn the remnant of the bolt... hot air paint stripper (or a hairdryer) will do the job, soak the remnant in WD40 (other penatrating oils are availible) for at least an hour then gently warm the spider, if you havent got a bolt extractor then try a self tapper screw (at least it's mild steel, ergo can be drilled out) you would be surprised how effective this can be. Don't over torque the self tapper going in and don't heat it either.. the temp differential can be just enough to persuade locked threads to free off...
just a thought...
Otherwise rachels shaped charge idea sounded good 