I’m stumped by this, hope someone can help!

The left crank on an SLX crankset came loose on the bike during ride. The splines in the crank were fairly buggered from wobbling around loose so I bought a replacement – the drive side was still OK as it seems to be the stronger metal of the two.

I’ve come to install it, and I can’t get enough of the drive side to come through the bottom bracket to get the safety pin to engage on the crank.

I’ve fitted tonnes of bottom brackets and cranksets before, the bike was faced last year and still looks smooth, and I’ve measured the BB spacers and they are 2.5mm as they should be (2 of them on the RHS, one on the LHS – it’s a 68mm BB).

I can only think the bearings have expanded somehow, or the drive side is damaged and not engaging fully – but I can’t see anything obvious wrong with it…

This photo shows the drive side fully engaged (after hitting with a rubber mallet to be sure!) – it doesn’t look far enough through to my eyes:

Help!

So you’ve just replaced the none driveside crank arm, and everything else is the same as before?

So that driveside crank (with axle) was previously installed in that bottom bracket? And now it won’t go in?

Have you gone at it with a soft-faced hammer?

Hit it (rubber mallet or soft hammer), the drive side is still too far out, theirs another couple of mm to go.

righty-tighty lefty-loosey?

Try giving it a tap with a) a rubber mallet b) a piece of wood beteen it and a hammer

So you’ve just replaced the none driveside crank arm, and everything else is the same as before?

So that driveside crank (with axle) was previously installed in that bottom bracket? And now it won’t go in?

Yep, same driveside, same bottom bracket, all that’s changed is the left-side. I took the BB off to grease it while I was there, but it’s back on tight against the frame, with the spacers in the same place. It’s like it’s breathed out or something!

Hit it (rubber mallet or soft hammer), the drive side is still too far out, theirs another couple of mm to go.

It’s had a proper bashing with a rubber hammer, it doesn’t want to go any further. Even tightening the pre-load bolt onto the crank doesn’t pull it far enough 🙁

take one of them drive side spacers out. Prolly the reason it fell off in the first place.

take one of them drive side spacers out. Prolly the reason it fell off in the first place.

According to the manual, a 68mm BB with a band-derailleur needs two on the drive-side:

http://bike.shimano.com/media/techdocs/content/cycle/SI/SLX/SI_6PZFA_002/SI-6PZFA-002-En_v1_m56577569830647029.pdf

I’m fairly sure this has always been the case?

It’s ok, the Shimano police wont come and get if you take out a spacer 😉

Remove spacer, re-install and if it’s works good and if it doesn’t you’ve not lost anything. Although, from your 2nd photo it does look like the axle still has further to be pushed in

that crank doesn’t look like it has the hole in for the safety pin to engage with?

I’ve got an early XT crank and it doesn’t have one – the originally spacer thing didn’t have a pin in it either.

[edit] actually the hole will be the other side, won’t it. d’oh.

have you changed the bearings in the cups at all – and i dont mean between chainset i just mean ever

well take the nondrive side one off. (Assuming the crank is pushed all the way in) you’ve too many spacers in there, if you cant get the crank arm on.

Check that your BB is definetly a 68mm??

Wouldn’t have though you you need to take any spacers out if its a 68mm as shimano is 2 drivside and 1 non drive side (I have that on many bikes). Sram is different though.

Does the end cap screw in at all?

Check that your BB is definetly a 68mm??

+1

Is it possible that the replacement crank is not compatible with the drive side crank? Ie the spec has changed between years?
Also sensible to check measurements on BB and spacers but you seem to have it covered. You either have 68mm and 3 spacers or 73 and one spacer – exceptions do not exist with Shimano. If it doesn’t fit something else is wrong!

Stopper plate on the wrong way round?

Is the inner face of the DS hard up against the BB outer plastic seal?

How about inserting the DS crank into the NDS and see if it goes all the way through?
Its not jamming on a chainring or something is it?

Has the bearing dust cover come off when you removed the cranks and now wont go back in properly?

It’s ok, the Shimano police wont come and get if you take out a spacer

This was what I was tempted to do – although I can’t figure out why it used to work – unless the last shop to fit it bodged it?! I was concerned the Shimano police might get me though :p

that crank doesn’t look like it has the hole in for the safety pin to engage with?

It does have the hole, it’s hidden at the bottom in the picture 🙂

have you changed the bearings in the cups at all – and i dont mean between chainset i just mean ever

I don’t think the bearings are really serviceable in these ones are they? The BB itself is less than a year old, and still spinning well.

Check that your BB is definetly a 68mm??
Wouldn’t have though you you need to take any spacers out if its a 68mm as shimano is 2 drivside and 1 non drive side (I have that on many bikes). Sram is different though.

Does the end cap screw in at all?
It is definitely a 68mm – I checked just in case. It’s always had two spacers on the drive side, something’s definitely changed. I’m happy to ditch one spacer if need be, I’m just a bit concerned it worked this long with two spacers!

The end cap screws in all the way – to the point it is flush with the crank.

Stopper plate on the wrong way round?

Good call, but definitely the right way – the ‘open’ side is facing outwards.

Is the inner face of the DS hard up against the BB outer plastic seal?

How about inserting the DS crank into the NDS and see if it goes all the way through?
Its not jamming on a chainring or something is it?

Good idea – tried pushing it through the opposite side, but it’s still not through as much as it should.

Has the bearing dust cover come off when you removed the cranks and now wont go back in properly?

Tried taking the cups out and wacking the bearing seals with a rummer mallet. They moved a bit, but not much – they certainly didn’t look proud. Still didn’t fit when I tried them back on the bike though 🙁

I’ve admitted defeat and removed one of the drive-side spacers.

I can only assume the shop that faced and fitted the BB originally were forced to bodge it somehow (maybe breaking off the safety pin on the stopper plate to get the crank to fit). Like me they probably couldn’t work out why a 68mm BB needs only two spacers instead of three – it’s a new one on me!

Thanks for all the suggestions – maybe one day I will know why this BB is fatter than most 🙂

Have you checked that there is nothing at all on the axle stopping you from pushing it in further?

You need to try another driveside crank in the otherwise unaltered setup, so you can discount there being a fault with that part.

If that part is not to spec then the shop that fitted it ( I assumed earlier that you had done it) might have bodged it upon finding the same issue as you’re doing now, and that bodge is what caused the crank arm to loosen.

If it isn’t right, it might eat another crank arm and keep costing you money. Better to actually find and rectify the actual fault than find a work around that masks the symptoms.

Can’t see from your pics, but it is an MTB BB that you have, isn’t it? Road BB cups look similar, but they’re wider. Could be the cause of your problem.

Have you checked that there is nothing at all on the axle stopping you from pushing it in further?

Yep, nothing unusual I can see – it’s smooth and there’s nothing sticking out on the chainring side.

You need to try another driveside crank in the otherwise unaltered setup, so you can discount there being a fault with that part.

I think I will take it to a different shop, and get them to try a new axle to see if it makes any difference. I am also very aware my new crank might get eaten by something wrong with the rest of the setup 🙁

Can’t see from your pics, but it is an MTB BB that you have, isn’t it? Road BB cups look similar, but they’re wider. Could be the cause of your problem.

Good call, but it definitely says ‘Mountain’ on it. Maybe it’s converted to a road one overnight when I left it?! Bloody thing.

w1zard did you get this sorted?

I ended up removing one of the spacer rings. I just wanted to get out and ride – you know how it is…

I haven’t died yet, but I’m also not particularly trusting of it either!

You may well bugger the crank / bb / bb shell doing that, there more than likely wont be enough preload on the bearings so they may wobble, come loose and strip the threads in your shell.

If you can’t fix it / install it correctly yourself get it to a LBS otherwise it may turn out to be a rather expensive bodge.