Even with no tension at all in the front mech cable, it won’t shift to the smallest ring.
It appears that the black plastic body of the mech is clashing with the seat tube, almost acting like a limit screw.
It used to shift down when I used to ride it about 5 years ago, but since I started using it again a few months ago, it has never shifted down.

Where am I going wrong?

You can see the small mark on the seat tube on the second pic, where the mech touches

[/url] Untitled by GreasyChipKarate, on Flickr[/img]

[/url] Untitled by GreasyChipKarate, on Flickr[/img]

Just thinking aloud (and having never installed a BB before), could it be that the drive side of the BB needs to be wound out a bit so that the chainrings are further away from the mech?
Can’t think of what else to try.

Turn your limit screw out and it will drop down straight away 🙂
One of the cross head screws on top 🙂 …. ones high and ones low limit screws ..

I’ve wound the limit screw out completey, but the mech (the black plastic bit here the limit screws are) is actually touching the seat tube, so wont move any further over in any case.

Is the cage parallel to the rings? In the top picture the back end looks to be pointing out wards slightly?

Have u wound out the screws with the cable detached ? … no reason why it shouldn’t drop down then

Have you installed a new BB and is it square taper?

I restored a 91 Rocky Mountain and I had the exact same problem, turned out the BB axle was 3mm too short.

… and new cables? Did you install a new cable when front shifter was in the centre ring position?

Ian, it was parallel, but I twisted it over to see if I could get that extra mm just to make it shift. The chain now rubs on the mech, but still won’t shift. Can’t see how I can get the mech to actually line up with the small ring, due to the clash of the mech with the seat tube.
strange

Not installed a new BB, but it had new cables just before i started using it again.

It had a service at the same time, and wasn’t shifting down after the service, but I didn’t get chance to take it back.

I wonder if they changed the BB at the service, although I definitely didn’t get charged for one, and it wasn’t mentioned when I picked it up.

Robdob, that sounds like the most obvious cause. Those 3mm would make all the difference. I’ll investigate, cheers.

I had this problem on my Intense- i fixed it by fitting a headset like spacer on the drive side of the Bottom Bracket. Should work with ISIS or Hollowtech.
Basically it moves the chainrings out a bit 😉

I have taken the caps off the crank bolts, and realised that my ISIS crank puller wont work on a hollowtech crank 😳

It looks pretty gnarled up in there though, with mash up aluminium. I wonder if the crank bolt has been wound so tight it has crushed and moved the crank in too close to the BB. The cranks have been really creaky going uphill out of the saddle.

Time for the LBS I think.

Cheers for the help.

If the only difference is new cables then I think to much cable tension. Make sure the adjuster barrel at the shifter is fully in or disconnect the cable and see if it works. If there is to much tension the lower limit screw will effectively do nothing.

Obviously its nothing to do with cables or tension or limit screws people!

The mech is as far over as it will go (touching the seat tube), no matter what you do to cables or screws its not going to move the mech any further! So it must be that the chainrings are too far in. Whack a spacer in the BB, problem solved 🙂

Chrisdw +1, clearly we were getting as frustrated as each other with the total lack of reading going on 🙂

Has the mech been raised?
The indentation of the outer cage plate should push the chain off the middle ring. It then widens at the bottom so it doesn’t rub while in the granny ring.
Try repositioning the mech lower down the seatpost and swing it out checking that the cage clears the big ring by about 1mm or as close as you dare. If you’ve put a larger big ring on then you might have a problem.

The other limit screw?

Failing that twist it so it’s at an angle. Or put a 3mm spacer on the BB.

Cheers guys.
Conkers, yes it is set up with 1mm clearance on the big ring.

I managed to get the cranks off by putting a woodscrew through the hollow crank bolt on the other crank, and using the crank puller (with a hole punch extender) to get the crank off.
There is no wear on the splines connecting the BB to the crank, so that can’t be squashed up, as I had suspected. There does appear to be more BB axle poking through on the non-drive side compared to the drive side. Is there a way of adjusting the position of the axle in the BB so that more pokes out on the drive side?

That would solve my problems.

Untitled by GreasyChipKarate, on Flickr

Untitled by GreasyChipKarate, on Flickr

Untitled by GreasyChipKarate, on Flickr]null

[/url] Untitled by GreasyChipKarate, on Flickr[/img]

Axle seems very short drive side ?

It also seems strange that on the drive side, BB splines are internal, on non-drive side BB splines are external.

Is that normal?

Well,
Having not taken a BB out before, I was a bit confused as to where or how to install a spacer.
I have now got the BB out, and have figured it out. There is only about 10mm of thread on the cartridge, so a 3mm spacer will reduce that to 7mm, which is a bit of worry. There must be a lot of force going through that thread.
I presume BB spacers are a stock item at the LBS? We’re going on a ride tomorrow afternoon, so hope so!

Thanks everyone for your help, I’ve learnt a lot tonight.

To close this one out, I have just put a 2.5mm spacer in, as suggested, and everything is working fine.

Thanks to the chaps at Biclycle Doctor for sorting me out this morning. Untitled by GreasyChipKarate, on Flickr