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Removing "threaded" cranks

by farrell
Thu, Jul 07, 2011 15:27
8

Trying to get the cranks of my mtb but when using the crank extractor rather than taking off the cranks it just took the thread off instead.

I've had a look around the net to see if there are any hints or tips to get the sods off now but it just seems to be people saying "buy a crank extractor" followed by "Yeah man, just buy the tool, its only like 10 bucks". Which is of little use to me now.

I've also seen people advising to pour boiling water on the cranks, which seems a nice theory but I cant see it actually working.

I've given them a bit of a wiggle and a yank along with some light tapping with a hammer and some sprays of WD40 and it doesnt seem like its going to budge.

Ideally, I'd like to keep the cranks so I'm looking to avoid bringing out the mjolnir and going full whallop but its looking increasingly likely that this could be the only option left unless anybody has any suggestions?

Farrell

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8 comments

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farrell | 13 years ago
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To be fair, I've just kept going on them and probably racked up another 200 miles on the bike, they are most likely due to completely fail very, very soon and I'm pretty sure I know the hill they are going to go on too.

Payday this weekend so it'll be hammer and chisel the sods off time and replace them.

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wodge | 13 years ago
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This sounds like a lot of trouble to get some extra riding in before pay-day.

The cranks are trashed, so you don't have much to lose by grinding them off.

You want to replace the BB, so even if you accidentally cut into the BB spindle while grinding the cranks off you have lost nothing.

When you've removed the cranks and fitted a new BB do you really want to risk wrecking the BB next time you want to remove the cranks?

If you really want to reuse the cranks I suggest blow torch + mallet and cold chisel, although I wouldn't bother myself, as it's just storing up some more trouble for later on.

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farrell | 13 years ago
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Oh, dont you worry, I've gone and threaded both sides.

If its a job worth getting wrong, its a job worth getting wrong completely.

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oldgit | 13 years ago
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You simply didn't screw the extractor in enough - probably.
If it's a sealed bottom bracket you're in trouble, and the only way you'll get them off if you really want to save them is to borrow a small automotive type crank puller.
If however it's an old style bottom bracket with cups and lockring it's not a big problem. Assuming you've not threaded both cranks?
With these loosen the lock ring, then loosen one of the bearing cups. now the axle will be moveable even if it's just a few milimetres. Pack something like cone spanners betwen the cranks and the cups. Then using something as a drift tap the axle once and the crank will just fall off.
Hope that makes sense. I have to do that with a nice 1940s race chainset I have.

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farrell | 13 years ago
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The extractor was a Park tool one and then I tried a cheaper one which almost got it but then essentially finished off the stripping job of the Park tool. I tried a Halfords extractor too but by that point it was as much use as tits on a tom cat.

I took it for a ride for about 10 minutes with the bolts off to see if it would work free but it stayed stuck, going to give it another attempt this evening but I reckon its stuck for good.

The only reason I want to save the cranks is that I cant really afford a new set before this weekend and I want to replace the bottom bracket before taking it out. In a week or so I'll be able to buy some new ones so wont mind obliterating them at that point quite as much.

I think I'll be chancing it with a suspect bottom bracket at the weekend and then setting about it next week.

Thanks for the advice and suggestions.

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Jonty79 | 13 years ago
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I had the same problem recently on a MTB rebuild. A blow torch, big hammer and a lot of cursing solved the problem! If you want to save the cranks I'd take it too a good LBS. Their mechanic will be too proud to resort to cutting anyway!

Good luck

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dave atkinson | 13 years ago
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Aluminium expands more than steel when heated. So the boiling water theory has some merit: if you heat both up, the hole in the crank will get bigger at a faster rate than the square taper, allowing it to work loose.

Use a penetrating oil such as Plusgas, leave it overnight, then go after it with the hottest heat source you can that *definitely* won't damage your frame; a hairdryer is a good bet. give it some persuasion with a mallet; if you can, apply force to the square taper not the crank arm by using a cold chisel or similar on the back face of the crank and you may have some luck. if not, time to crack out the Dremel Multi and make some incisions, i'm afraid...

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SideBurn | 13 years ago
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Sorry to be a pain, but now you have damaged the thread in the crank it is pretty useless. If you ride around on it it will eventually come loose and fall off, but if you re-fit it you will have the same problem again. Try borrowing other makes of extractor (better quality)that may have a better or more chunky thread on them, you may not have damaged the tread completely. Otherwise you will need to bite the bullet, cut the crank off and buy a new one...I bit the bullet cut the crank off and bought a new one...It was a nice Campag crank that is now hanging on the wall to remind me to do the job properly with good quality tools in future! Good luck

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