Front mech problems following chainset swap

Jamieg285

I recently discovered that my old chainset was subject to a recall by Shimano. I took it to my LBS and they arranged for it to all be replaced - result!

However, having got the bike back I am having difficulties with the front mech shifting to the smallest ring. I've replaced the cable and adjusted the stops, but it's making no difference.

I've tried a search on here and got some info, but I could do with a bit more knowledge before I take it back to the LBS.

The original chainset was 24/34/42, but the new (Alivio 8sp) is 22/32/42. Could the smaller middle ring account for the shifting problem?
Is this something that can be adjusted, or do I need a new mech that is compatible with the smalerl size middle ring, which appears to be standard. I've had a brief look, and it appears that a 32 middle isn't that common now.

nicklouse

part numbers of old and new?

and the middle ring would have been 32 but it has no bearing on setting up gears or the way they work.

Jamieg285

Bear in mind all the original equipment was of 1997 vintage...

Old chainset was FC-MC12 Alivio, and it was definitely the tooth count stated above.
New chainset is FC-MC10 Alivio.

Mech is currently the original FD-M291 Acera.
http://www.greenwich-market-trader.co.u ... =US&LAG=en for an example and confirmation of the original chainring sizes.

Wooliferkins

Have had a similar problem with my colleagues tourer. Nick; In essence I agree with you but in practice... We replaced the worn middle chainring on my colleagues 105 triple a ring with 2 teeth difference ring. Nothing we did would make it change properly much less smoothly. Change back to the original size ring all is sweetness and light. I know it should work but I think the sweep of some Shimano triple front mechs is so precise as to not allow much but the prescribed ratios. I'm surprised to find this at Alivio level but a possibility.

supersonic

What bottom bracket lengths do these chainsets require? Some front mechs have a habit of bottoming on themselves, and not the stop, so if the chainline is now too large, this could be the rpoblem.

Jamieg285

BB lengths is getting a bit beyond my level of knowledge.

I do know that the original chainset had a 47.5 chainline, and the new one has a 50, but I believe that this can be allowed for by the spacing on the BB, which incidentally was also changed at the same time. I have assumed (but will measure it before I go back) that the LBS have set the chainline correctly.

Even so, based on those figures, the rings would be further away from the frame and make it harder to get to the top ring, not the other way around. If the mech has it's stop fully out and it's still not shifting down, it implies either the rings are too far in (unlikely), or there is a problem with the mech...

supersonic

Sorry, I meant too small. You may need a longer bottom bracket axle.

Shimano tech docs should show what axle you need for your chainset. Then compare to what you have.

Jamieg285

How do I identify/measure the BB when it's installed?

If it is too short, would it show up if I measured the chainline?

supersonic

Take it out and measure I am afraid.

The chainline measurement is usually a good indicator. Shimano measure to the inside face of the middle chainring.

Jamieg285

Measure what exactly? Total width? If so, can that be done installed, i.e. remove pedals and measure end to end?

Sorry for all the dumb questions, but a lot of this stuff is all new to me.

supersonic

The length of the axle. Sometimes stamped into the bottom bracket itself.

Either way, if not working, and they fitted it, take it back.

Jamieg285

Had a closer look tonight. Checked the chainline and it is 50mm, but I don't think that's the problem.

It's looking more like what Wooliferkins suggested. When on the middle ring the chain is just below the bulge in the mech that would push the chain when shifting down. If I lift the chain slightly whilst turning the cranks it shifts as expected. Looks like the mech isn't compatible with the chainset.

Disappointed that the LBS didn't spot this, as it's a pretty obvious flaw. They clearly haven't made any attempt to setup the gears after installing them.

Will see that they have to say for themselves tomorrow.

supersonic

Is the mech at the correct height? It should clear the outer ring by 1-2mm.

cooldad

I'm more interested in how they recalled a 1997 chainset. That's 15 years.

supersonic

I remember the recall, poor quality crank arms that fractured.

Jamieg285

The mech is at the right height. The outer ring is the same size as the original, so the height remained unchanged.

You're right about the recall, it was back in the late 90's. I'm just amazed that they still honoured it after all this time.

supersonic

Have you got the exact code of the front mech? SOmething I can check.

Jamieg285

FD-M291 is the number stamped on it. Is there anything more?

cooldad

Acera X. Max capacity 18t, new chainset is 20.

cooldad

Should still work though.

supersonic

There is nothing in the specs that suggests this mech will not work - large/middle cog difference is listed as 8t minimum. 10t should not be a problem at all, though 8t does mean the shifts to the inner are slightly better.

If you have got a new chainset though it pays to get a new chain, as you can quickly wear it out. This may be contribute to shifting probs as well.

I think a thorough check of the mech angle, height, chainline and a new chain will solve it.

Jamieg285

The LBS didn't want to know. First guy looked at it, ignored what I had to say. He took it out back to check it, claimed he'd fixed it by altering the stops (odd being the only tool I saw him use was a crowbar!) Took it for a quick spin and unsurprisingly it was no better.

Next the manager took a look and took it for a ride himself. Claimed it wasn't that bad, but them he came out with a card that I couldn't dispute, saying it was because the mech was old and worn.

If that was the case, I would have had the problems before the rings were changed. Can't prove it either way now, so I'm going have to fork out for a new mech myself now. At least they don't cost much.

supersonic

Very odd they remember a 15 year old recall, yet will not set it up after.

Warranties have implicit terms - they do not affect your rights, but if the shop took on the work, I would expect that they make sure it worked. Or at least they worn you of any problems.