How do I remove this crank?

[Roboshu78]

Hi all
I am restoring an old mountain bike and want to take off the cranks but my normal crank removal tool doesn't appear to fit these cranks. The hole is too small. I have attached a picture.
Any ideas?
Thanks
Robin

[Brucey]

that looks like a self-extracting crank. the idea is that you get a standard metric bolt (do check but M12 from memory) and use that to push the crank off. IIRC it kind of works, but there is every chance that the threads on the bolt will get mangled/stripped and that even if this doesn't happen the end of the bolt will be burred over so it will need to be ground down before and/or after it has been used, else it won't come out of the crank afterwards.

Such cranks are usually very cheaply made and best filed under 'B' for 'bin'.

cheers

[alexnharvey]

Could it be a self extracting crank bolt gone wrong? Are there two holes on the outer face of the silver part to remove it? Possibly under a plastic cover.

[andrew_s]

Self-extracting crank bolts are allen key crank bolts that have a flange on the side, something like 16-17 mm across. When the bolt is fully home, a collar is screwed into the regular crank remover threads (using a pin spanner in 2 small holes), so that when the crank bolt is undone, it just hits the collar rather than unscrewing all the way out.
If you keep on unscrewing, something has to give, and it's normally the crank taper that gives first, with the flange pushing the crank off.

I say "normally" because I did have a set of self-extracting bolts where what gave was the threads on the collar, leaving me to remove the bolt, spend some time picking bits of swarf out of the crank threads, and use a normal crank extractor.

If it is a self-extracting crank bolt, it's a matter of keeping on unscrewing it with a 6 or 8 mm allen key, as appropriate.
It will be tight at first, then move easily for a turn or so until the flange on the bolt reaches the collar, and then be hard to turn for about 2 full turns whilst the crank gets pulled off the taper.

The alternative is to remove the collar, remove the bolt, and use your normal extractor.

I use normal bolts, but I've a single self-extracting bolt and collar in my touring toolkit, to give me a chance if I should ever need to get a crank off away from home.

[Brucey]

IMHO this isn't a 'normal' self extracting crank bolt, it is a self-extracting crank. These are cheaply made steel cranks with a built-in female thread for a big bolt to be used as an extractor. If you have never seen one of these, count yourself fortunate; they are fairly horrible things....

cheers

[rjb]

If you dont have a crank remover you may find that if you ride the bike for a while it will come free of its own accord as the retaining bolt appears to be missing.

[Roboshu78]

Thanks all. Much appreciated.

I suspect it is a 'self extracting crank' as Brucey has suggested. My biggest bolt is one size too small (frustratingly) so I am going to take it to my local bike shop tomorrow.

Thanks again, very useful.

Robin