Extracting cranks

El Gordo
El Gordo Posts: 394
edited February 2009 in Workshop
I've managed to strip the threads on my LHS crank (square taper) so can no longer get the exrtactor to work. Yes, it was screwed in correctly and no, there wasn't a washer in there but when I wound the tool up to pull the crank off the tool just pushed the threads off instead.

Any bright ideas as to how I can get it off? Since it's wrecked anyway it's destined for the bin so the method can be nice and destructive! I've tried a lump hammer and cold chisel but no joy. I suppose there is always the hacksaw but I'd be nervous about going into the axle!

Comments

  • term1te
    term1te Posts: 1,462
    Hi when I've done this in the past, I've used a fork like device which I believe is for separating ball joints, and a big hammer. A bit like a two pronged chisel. Worked a treat, but did mark the outer face of the BB. Wouldn't recommend it if the BB is not metal. Less than five quid from Halfords a few years back.
  • careful
    careful Posts: 720
    You could try getting some heat to the crank, maybe by laying the bike over so that the crank is lying in a tray of hot water. You might even risk very careful use of a blow lamp. I would guess that the axle/bearings will have been damaged already by the hammer & chisel impact. I would go for the hacksaw method and fit a new axle. At least that way your frame is not at risk. Good luck.
  • Monty Dog
    Monty Dog Posts: 20,614
    Ball joint splitter is easiest - the problem with sawing is not damaging the frame. Next time, make sure the crank extractor is screwed fully home , otherwise the laod is taken by a few threads with the resulting problem.
    Make mine an Italian, with Campagnolo on the side..
  • I'd deep-score it with V-slots on two opposite sides with a Dremel and then get a chisel into the cracks with a big hammer! Avoids touching the bracket and should split it.

    Try putting a slotted piece of cardboard against the bracket, just to be safe.
    AT MY AGE, I SHOULD KNOW BETTER !!!
  • I had a similar problem a while back. Firstly I just ignored it until the point where the bottom absolutely had to be changed (this bought me an additional three years) and then I got an angle grinder and chopped the crank off. I made a cut down through the crank aiming parallel to one of the faces of the bottem bracket axle. Once this was done the crank just fell off.
  • balthazar
    balthazar Posts: 1,565
    Simplest: ride bike around for a while, within walking distance of home. The crank will fall off eventually.

    Most definite: Blowtorch. Heat up the crank the tap it off with a hammer and drift.

    Possible, depending on the gods: bearing puller -

    bearingpuller.jpg

    I've used one of these before, but I've seen them break too, so I wouldn't buy one specially.
  • El Gordo
    El Gordo Posts: 394
    Thanks for all the advice. I'll probably try a bit of heat first (very carefull use of blowtorch I think). If that doesn't do it then the ball joint splitter may do the trick although it's on the plastic cup side of the BB so that would get pretty knarled up in the process.

    Riding around on it for a while could work (I'd probably put the bolt back in loosley just in case - that's an accident I really don't want to have). The annoying thing with that though is that I've already fitted the drive side new crank and the square hole is at 45 degrees to the old one so I'd have to swap back to the old one.

    I suspect the bearing puller would cost as much as a new BB so if it comes to it I would just hacksaw through the axle!
  • crankycrank
    crankycrank Posts: 1,830
    Wrap a wet towel around the BB between the crank arm and frame. Hold the bike by the crank parrallel to the floor and use a blowtorch. The wet towel should protect the BB and frame from getting too hot. With any luck it should seperate. Don't hold the bike too high of course. :wink: