How do you get off a crank with a stripped thread?

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busaste
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How do you get off a crank with a stripped thread?

Postby busaste » 28 Feb 2009, 7:22pm

It was not me who stripped it. Honest!!!
I tried with my extractor tool but no chance, the thread is too mashed up. I would rather not hammer it off from the back as it is a 33 year old rare Viscount crank. Is there such a thing as an extractor tool for cranks where the thread has been stripped? Any other methods?
Thanks!

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Mick F
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Re: How do you get off a crank with a stripped thread?

Postby Mick F » 28 Feb 2009, 7:29pm

An idea is to pull the other one off, then undo the BB, pulling the BB spindle and/or bearings with it. Then, with it off the bike, you can operate on it a little better without damaging or affecting the bike frame.

See if you can get the BB spindle in a vice and use a puller or wedge behind the crank, using the vice as a base. Also a LITTLE heat from a heat gun or GENTLE blowlamp onto the alu crank around the area may help.

But really, the crank has had it, unless someone could re-thread it.
Mick F. Cornwall

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robwa10
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Re: How do you get off a crank with a stripped thread?

Postby robwa10 » 28 Feb 2009, 7:57pm

I know someone who said they used a bearing puller to get off a stripped crank. They can be expensive though so you might not want to go that route.

I had the same problem, I did strip the thread :oops: , and I had to take an angle grinder to the BB spindle and crank arm. If I remember correctly I mainly cut the crank arm where the threads are and eventually just cut off one side so that the crank arm only had three sides touching the spindle. I was then able to lever off the crank. I kept topping frequently and putting water on it to keep it from getting to hot and damaging the frame. It took awhile but I think I didn't cut the spindle because it was hard to get to and was a harder metal.

PW
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Re: How do you get off a crank with a stripped thread?

Postby PW » 28 Feb 2009, 8:28pm

I've used the bearing puller. It's basically a nut hinged onto 3 hooked arms. There is a long hardened bolt which screws through the middle. You can buy these for a fiver off the fleamarket. Get two, with different length but interchangeable arms. That way you can concoct a hybrid to get a good grip on the chainring spider.
If at first you don't succeed - cheat!!

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ferrit worrier
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Re: How do you get off a crank with a stripped thread?

Postby ferrit worrier » 28 Feb 2009, 8:43pm

Use a two arm bearing puller, insert the holding in bolt into the bottom bracket spindle but dont tighten it, have it loose by a couple of threads, hook the lips of the arms of the puller behind the crank boss, because your possibly pulling on to an alloy crank slip a piece of card between the arms and the crank, (this is one of those jobs you need three hands for!) this will help to reduce any damage to the crank. if you've got a small "G" clamp hold the arms onto the crank with one. this will give a positive location for the arms, and as your crank boss is probably rounded on the corners it will stop the arms being pulled off round the crank. tighten up the screw and hopfully it should "pop" off.

Hope it works

Malc
Percussive maintainance, if it don't fit, hit it with the hammer.

rjb
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Re: How do you get off a crank with a stripped thread?

Postby rjb » 28 Feb 2009, 9:19pm

If the bike is still rideable just loosen the crank retaining bolt and ride it around. Cranks can work loose through use. If not then resort to a bearing puller.
At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, 2 Dawes Kingpins, Raleigh 20, Falcon K2 MTB dropped bar tourer, On One Pompino, Longstaff trike conversion on a Falcon corsa. :D

freezing77
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Re: How do you get off a crank with a stripped thread?

Postby freezing77 » 28 Feb 2009, 10:56pm

I have had exactly the same problem and made up a tool in the shape of an acutely angled wedge with a slot in to fit over the bottom bracket.

I then used spacers between the crank arm and bottom bracket to ensure a neat fit, and then as the saying goes applied some impact technology to the wedge. The cranks had not been removed for many years but this method removed them, the advantage of using a wedge as opposed to hitting the crank directly is that the hammer blow are taken by the wedge and transmitted over a wide area to the crank. A picture would perhaps explain it better.

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andrew_s
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Re: How do you get off a crank with a stripped thread?

Postby andrew_s » 28 Feb 2009, 11:32pm

freezing77 wrote:I have had exactly the same problem and made up a tool in the shape of an acutely angled wedge with a slot in to fit over the bottom bracket.

I then used spacers between the crank arm and bottom bracket to ensure a neat fit, and then as the saying goes applied some impact technology to the wedge. The cranks had not been removed for many years but this method removed them, the advantage of using a wedge as opposed to hitting the crank directly is that the hammer blow are taken by the wedge and transmitted over a wide area to the crank. A picture would perhaps explain it better.


Might not a ball joint separator, or even two in opposition, be used the same way?

In fact there seem to be a variety of ball joint tools that may be usable
eg
http://www.justoffbase.co.uk/Ball-Joint ... ategory=99
http://www.justoffbase.co.uk/19mm-Capac ... ategory=99

PW
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Re: How do you get off a crank with a stripped thread?

Postby PW » 1 Mar 2009, 1:21am

I know of a frame builder who uses the wedge technique. He is a highly competent chap who I'd trust with my life - well he built my 953! :D But I would NOT use that method myself unless in extremis, the risk is too high for a top notch frame.
If at first you don't succeed - cheat!!

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Mick F
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Re: How do you get off a crank with a stripped thread?

Postby Mick F » 1 Mar 2009, 8:35am

As I said, get it off the frame, complete with the stuck spindle.

The trouble is, if you have a "modern" BB, the sort where you need a tool that you insert into the cup, you can't! "Traditional" BBs can be done easily.
Mick F. Cornwall

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robgul
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Re: How do you get off a crank with a stripped thread?

Postby robgul » 1 Mar 2009, 8:57am

Have a look at www.beewee.org.uk and the Briefings section - there's a few tips there that start out with boiling water and progress to a cold chisel!

Rob

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Phil_Lee
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Re: How do you get off a crank with a stripped thread?

Postby Phil_Lee » 1 Mar 2009, 4:23pm

A decent bearing puller will have a collar which you can screw down to hold the legs in place behind the crank arm while you tighten the bolt onto the spindle.
It's still best to put something under the hooks to protect the crank arm though, as they can still scar it, even without slipping.
Once it's tight, tap the end with a hammer to help shock the taper free, rather than apply too much brute force to the screw.

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bigjim
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Re: How do you get off a crank with a stripped thread?

Postby bigjim » 1 Mar 2009, 10:12pm

take it to the LBS. My bike is in there now with the same problem. He informs me that he comes across this all the time. Evidently aluminium goes soft as it ages and the crank puller just strips the thread. just a two minute job for him and all helps to keep lbs from dying out.

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Mick F
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Re: How do you get off a crank with a stripped thread?

Postby Mick F » 1 Mar 2009, 10:19pm

bigjim wrote: ...... aluminium goes soft as it ages ........


News to me!

How old do cranks have to be before a crank puller strips the threads?
I have a chainset well over 20 years old, and the threads are absolutely fine. I pulled them off their BB only a couple of days ago.
Mick F. Cornwall

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CJ
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Re: How do you get off a crank with a stripped thread?

Postby CJ » 2 Mar 2009, 3:02pm

bigjim wrote:... aluminium goes soft as it ages ...

Nonsense. What happens is aluminium corrodes/welds onto steel, with time, absence of corrosion inhibitors and exposure to dirty water. Eventually the strength of the bond exceeds the strength of the thread.

It helps to put a very light smear of Copaslip (or Alumslip is better if you can get it) onto the axle before fitting.
Chris Juden
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