How do I get my chainset off?

For discussions about bikes and equipment.
neilob
Posts: 605
Joined: 31 Jan 2008, 3:58pm
Location: Notts/Lincs borders

How do I get my chainset off?

Postby neilob » 21 Jan 2018, 5:55pm

Like a complete eejit I have rounded the head of one of the two Allen bolts holding the left crank onto the axle. It is a fairly modern Shimano external bearing setup. Any reason not to drill out the head? But how do I then remove the threaded part? Any other ideas very welcome.
Using a car to take an adult on a three mile journey is the same as using an atomic bomb to kill a canary.

robc02
Posts: 1645
Joined: 23 Apr 2009, 7:12pm
Location: Stafford

Re: How do I get my chainset off?

Postby robc02 » 21 Jan 2018, 6:22pm

Before drilling:

1. Is there dirt at the bottom of the socket head? If so, clean it out with a sharp screwdriver or similar then tap in an unworn allen key with a hammer. (Tap it because the mangled bits might stop the key from going in properly.) Then, pressing the key hard into the hole (o ensure it stays fully in), carefully turn it and with a bit of luck the bolt will turn with it.

2. Try the above with a slightly oversized (e.g. imperial) allen key).

3. Try to find a screwdriver with a blade the correct width to be tapped into the bolt head, then tap it in and turn it.

If you have to resort to drilling the head off: Can't you access the other end of the bolt on Shimano cranks? If so drilling into it from that end might drive it out once the head has been removed to release the tension. Or drilling, tapping and, if it hasn't loosened by now, insert a small bolt or screw to give some purchase. It is all getting a bit delicate by now though - with small diameter taps etc.
There are also various thread extraction devices available.

I have had success in drilling out small bolts - such as one of the dropout adjuster on Campag style rear dropouts. It is quite easy to drift offline and damage the female thread, but if you go carefully it can be done.

mattsccm
Posts: 2661
Joined: 28 Nov 2009, 9:44pm

Re: How do I get my chainset off?

Postby mattsccm » 21 Jan 2018, 7:14pm

Try smacking a Torx bit in. They often bite well in damaged allen sockets. Easier than drilling is a hacksaw throgh the slot. The head end will then drop out and you can do the rest in a vice. You can also use the unthreaded part of the hole as a guide for the drill.
Worked for me.

AndyA
Posts: 393
Joined: 21 Mar 2009, 9:16pm
Location: Edinburgh

Re: How do I get my chainset off?

Postby AndyA » 21 Jan 2018, 8:23pm

An impact driver (the kind you hit with a hammer) would be what I'd try first.
I have this one, it works well
https://www.machinemart.co.uk/p/cht498- ... gInMPD_BwE
Drilling will work, but as you say you may struggle getting the rest of the screw out

Brucey
Posts: 35230
Joined: 4 Jan 2012, 6:25pm

Re: How do I get my chainset off?

Postby Brucey » 21 Jan 2018, 8:39pm

I agree with Matt; try tapping in a torx bit first of all. If the other bolt is still OK, leave that one snugged up whilst you attempt to loosen the bad one; it will take some of the load.

If you have to start drilling, you will most likely find that once the fastener tension is lost (i.e. you have drilled the head off the fastener) the shank of the bolt will unscrew without too much difficulty, eg using a stud extractor.

In addition, go through your toolbox, find the duff allen key that caused the trouble in the first place, and chuck it away. I have seen no end of mangled M6 capheads where someone tried to get them off using a 3/16" allen key.... :wink:

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

neilob
Posts: 605
Joined: 31 Jan 2008, 3:58pm
Location: Notts/Lincs borders

Re: How do I get my chainset off?

Postby neilob » 22 Jan 2018, 9:39pm

Got it off by tapping in an imperial size Allen key. Thanks for the advice.
Using a car to take an adult on a three mile journey is the same as using an atomic bomb to kill a canary.

User avatar
Gattonero
Posts: 3554
Joined: 31 Jan 2016, 1:35pm
Location: London
Contact:

Re: How do I get my chainset off?

Postby Gattonero » 28 Jan 2018, 11:48am

neilob wrote:Got it off by tapping in an imperial size Allen key. Thanks for the advice.


Next time what you can do is remove the other bolt, use a longer one (it's an M6) with a suitable spacer (say the bushing of a jockey wheel) so that in case you round it off you can always remove it; then tighten up this new bolt farly high, like 14-15Nm this will get the opposite bolt a tad loose then easy to be removed even if the hex is rounded.
And use a better allen key next time :wink:
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

User avatar
mjr
Posts: 13573
Joined: 20 Jun 2011, 7:06pm
Location: Norfolk or Somerset, mostly
Contact:

Re: How do I get my chainset off?

Postby mjr » 9 Sep 2019, 2:23pm

Relatedly, [moved to viewtopic.php?f=5&t=132632 ]
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
All the above is CC-By-SA and no other implied copyright license to Cycle magazine.

Jamesh
Posts: 573
Joined: 2 Jan 2017, 5:56pm

Re: How do I get my chainset off?

Postby Jamesh » 9 Sep 2019, 5:32pm

Invest in some decent Allen keys.

Cheers James

Manc33
Posts: 1388
Joined: 25 Apr 2015, 9:37pm

Re: How do I get my chainset off?

Postby Manc33 » 10 Sep 2019, 1:39am

I despise those stupid Hollowtech 2 crank arm bolts. 12-14Nm on a bolt with a 5mm allen head, really Shimano :roll:
Only weird bikes are interesting anymore.

drossall
Posts: 4539
Joined: 5 Jan 2007, 10:01pm
Location: North Hertfordshire

Re: How do I get my chainset off?

Postby drossall » 11 Sep 2019, 12:02am

I know the OP's bolt is out now, but I've found this kind of bolt extractor very good. The instructions often say to use a variables-speed power drill. I just use a ratchet-type socket driver. It's really just a left-hand thread that you drive into the rounded bolt, until it engages and turns the bolt out of the socket.