Removing broken bolt from crankset

jds_1981
jds_1981 Posts: 1,858
edited April 2015 in Workshop
Just managed to break one of the two bolts in the crank arm when trying to fit my new CX-70.
How best to try to remove? The less drastic the better.
Suppose I could try and glue another bolt on to the broken bit from the other end to undo.
I've also heard of drilling bolts out before, what's the general approach for this? Come in from the end opposite to where the bolt head was so that as you drill in it undoes?

Thanks.
FCN 9 || FCN 5

Comments

  • Mage Banan
    Mage Banan Posts: 24
    Did you lubricate the bolts when tightening them? Shimano don't specify whether the bolt torque is dry or lubricated. Lubricating greatly increases the bolt stress compared with dry for a specific torque and can snap bolts.

    Do the bolts have blue loctite on the threads?

    You can get left handed thread drill bits and screw extractors to remove snapped bolts. Screwfix sell some. You probably don't need anything that drastic as the bolt has not seized in the thread, you just need to get a bit of purchase so unscrew it. Your idea of drilling it with a right handed bit from the rear might work if you can do it without damaging the thread. Centre punch the tip of the bolt if you can get to it to stop the drill wandering and damaging the crank thread.
  • jds_1981
    jds_1981 Posts: 1,858
    Ah, managed to extract. Found a bolt of the same thead pitch that I put in from the other side, by turning, then backing off and tapping the broken bolt from the other side managed to get it out quite easily.

    The cause of the original issue was dumb reliance on tools. I've a Giant torque wrench I've used about three times in total. Seems that since I last used it, it has broken (been sat in the attic doing nothing), so the force was a lot more than it should have been. Should have just used a normal hex key as I was originally planning.
    FCN 9 || FCN 5

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