Crank Removal Problems

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Pebble
Posts: 1934
Joined: 7 Jun 2020, 11:59pm

Crank Removal Problems

Post by Pebble »

Went to pull the left hand crank off the UN55 square taper. The removal tool has ripped all the threads out of the crank (no I hadn't cross threaded it)

I'm thinking cut through square taper and buy new bottom bracket and crank ?

Any othe less drastic solutions ? I can get a two leg puller but doubt that will do the job, and a 3 leg won't fit.
Eyebrox
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Location: Ayrshire

Re: Crank Removal Problems

Post by Eyebrox »

With bike upside down, hold the crank upwards by gripping the pedal. Hit the base of the crank arm with firm but measured blows with a heavy rubber mallet.
drossall
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Re: Crank Removal Problems

Post by drossall »

A puller is the alternative I'd go for. Mine builds up in either two-or three-leg configurations. One or other usually fits, depending on the crank in question. There are some other tricks that people use.

But, as the thread is gone, I certainly have cut through the square taper before, on the basis that the crank may as well be scrapped. Chances are that won't damage the BB, because it's generally steel and you're cutting an alloy crank, which won't take so much pressure to cut, and will often give way before you're fully through. However, if the crank's stuck, the BB is probably due for replacement anyway. Even if the bearings aren't shot, the surfaces that mate with the crank may be, and you don't want another crank getting stuck on the same BB!
jb
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Re: Crank Removal Problems

Post by jb »

Place a steel drift (steel or brass bar or an old socket set long extension piece) on the crank as near the axle as you can then hit it hard with a 2lb hammer, the shock should shift it before too much damage to the aluminium crank occurs and it might be reusable. Don't brace the frame against anything when you do this, just get someone to hold it firmly otherwise you might bend it. Also put the crank bolt a few threads into the axle before hand so you don't knock the crank into the other persons face.
Cheers
J Bro
alanesq
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Re: Crank Removal Problems

Post by alanesq »

If you put some heat on the crank this should expand it and make it easier to remove
rjb
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Re: Crank Removal Problems

Post by rjb »

Remove the attachment bolt, ride bike and it may soon work loose. Carry a spanner and bolt so you can nip it up if it works loose a long way from home. :wink:
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X3, Raleigh 20 stowaway, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840 :D
Jdsk
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Re: Crank Removal Problems

Post by Jdsk »

jb wrote: 14 Apr 2021, 1:00am Place a steel drift (steel or brass bar or an old socket set long extension piece) on the crank as near the axle as you can then hit it hard with a 2lb hammer, the shock should shift it before too much damage to the aluminium crank occurs and it might be reusable. Don't brace the frame against anything when you do this, just get someone to hold it firmly otherwise you might bend it. Also put the crank bolt a few threads into the axle before hand so you don't knock the crank into the other persons face.
I can't picture this. In which direction do you whack the drift, please?

Thanks

Jonathan
rogerzilla
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Re: Crank Removal Problems

Post by rogerzilla »

A 2-legged puller is the best way to do it. You may need to put a crankbolt back in (loosely) to give the puller something to push against.

Alternatively, hacksaw the crank at the taper so you can split it. The axle is much, much harder to cut through.
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NUKe
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Location: Suffolk

Re: Crank Removal Problems

Post by NUKe »

Pebble wrote: 13 Apr 2021, 11:24pm Went to pull the left hand crank off the UN55 square taper. The removal tool has ripped all the threads out of the crank (no I hadn't cross threaded it)

I'm thinking cut through square taper and buy new bottom bracket and crank ?

Any on the less drastic solutions ? I can get a two leg puller but doubt that will do the job, and a 3 leg won't fit.
ride it for a short distance and the crank will probably fall off. if it doesn't then go for the Crank puller, A bit of heat may help,
NUKe
_____________________________________
Stradageek
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Joined: 17 Jan 2011, 1:07pm

Re: Crank Removal Problems

Post by Stradageek »

I took some good advice on this forum and whenever removing STCs I carefully insert the tool - pinch it up - screw in the extractor and pinch it up tight then hit the end of the puller with a small hammer.

When this fails (which it does very occasionally on very old cranks) and the thread is a gonner, I repeat the process but using a Unior tapered extractor.

A great tool that has never failed me

https://www.cyclestore.co.uk/unior_tape ... qjEALw_wcB
Pebble
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Re: Crank Removal Problems

Post by Pebble »

Indeed, a Tapered Extractor would be the tool, don't think I could justify the expense for a one off.

Would removing the bolt work on a properly tightened crank, I thought its only function was to push the crank on ?
do these bolts not occasional work loose and the whole idea of the plastic plug is so you don't loose the bolt o the road.

rogerzilla wrote: 14 Apr 2021, 8:56am A 2-legged puller is the best way to do it. You may need to put a crankbolt back in (loosely) to give the puller something to push against.

Alternatively, hacksaw the crank at the taper so you can split it. The axle is much, much harder to cut through.
As in hacksaw alongside of the taper, I would worry about damaging the taper then getting the next crank stuck.
Image

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As it is there is no great emergency to get it off. I was only removing the cranks to repaint that part of the frame, and I can do that with the left hand crank still attached. There could be many thousands of miles left in the currant BB.
Would still like a plan and everything in place for when it does need to come off.
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geomannie
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Re: Crank Removal Problems

Post by geomannie »

FWIW, my usual approach when removing a crank from square taper BB is to apply the removal tool as per normal. If however, I meet any stubbornness then I stop before the force needed to strip the threads (learned the hard way!). I then take the bike outside and empty a kettle of boiling water over the crank. This usually expands the crank enough to get it off the taper fairly easily. If its an expensive crank which I worry about, I might go straight for the boiling water straight off.

On the rare occassions that fails, then I have reverted to the hacksaw.
geomannie
jb
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Re: Crank Removal Problems

Post by jb »

Jdsk wrote: 14 Apr 2021, 8:39am
jb wrote: 14 Apr 2021, 1:00am Place a steel drift (steel or brass bar or an old socket set long extension piece) on the crank as near the axle as you can then hit it hard with a 2lb hammer, the shock should shift it before too much damage to the aluminium crank occurs and it might be reusable. Don't brace the frame against anything when you do this, just get someone to hold it firmly otherwise you might bend it. Also put the crank bolt a few threads into the axle before hand so you don't knock the crank into the other persons face.
I can't picture this. In which direction do you whack the drift, please?

Thanks

Jonathan
Well its a bit of "if all gentler attempts fail" method. Riding without the bolt works but not immediately - could be weeks.
The drift can be placed between the seat tube & the down tube so that one end is in contact with the part of the crank just before it becomes the square taper boss. you hit the other end which should be protruding a way off from the frame so you cant accidentally hit it if you miss. It should be sufficiently rigid so as not to absorb the blow and preferably have a bull nose end that fits into the crank hollow. A violent knock on the drift should jump it off without damage to the frame. Heating the crank first might help.

Tapers aren't like plain shafts- once it moves things can only get looser.

A bit like the the old breaking a piece of wood held between two wine glasses trick. The technique is to hit the wood hard a fast enough that it breaks before the shock reaches the glass.
This is from experience on one of my frames but maybe the bulkier type frames won't allow it?
Cheers
J Bro
Jamesh
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Joined: 2 Jan 2017, 5:56pm

Re: Crank Removal Problems

Post by Jamesh »

Loosen the bolt and wack it hard with a hammer whilst holding the Pedal should loosen it.

Cheers James
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foxyrider
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Re: Crank Removal Problems

Post by foxyrider »

Pebble wrote: 14 Apr 2021, 10:04am
Would removing the bolt work on a properly tightened crank, I thought its only function was to push the crank on ?
do these bolts not occasional work loose and the whole idea of the plastic plug is so you don't loose the bolt o the road.
The bolt does indeed pull the crank onto the taper but equally important, if its done up properly it keeps the crank in place. Riding with a missing or loose bolt will, usually in quite short order, allow the crank to move and extract itself - you'd have to pedal 100% 'round' with no lateral movement for it not to - as most of us have some degree of wobble in our pedalling action an unretained crank on a square taper is quite literally helped by our pedalling action (its not worked in a stand for me but every time when putting force through). Whilst it does work on flat roads, a bit of a hill will speed the process as you tend to exaggerate any pedalling movements.

Of course, you'll have to lightly refit so you can remove the pedal - remove it first then refit with a good bit of grease in the threads so you can do the extraction ride.
Convention? what's that then?
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