Front mech doesn't shift into big ring.

[Andy in Germany]

I've got a bike on the stand where the front mech doesn't have the throw to pull the chain into the big ring.

The stop screw is unscrewed fully. Infact it was ulike this when I started so I suspect the previous owner had this problem.
The cable is tensioned,
When I just pull down on the cable itself the mech won't go further across than it already is.

I've tried tightening the crank screw in case the chain ring is too far across but to no avail.

How would you go about solving this?

 

[Paulus]

Undo the cable from the clamp and see if the mech moves across the full range by hand.
If it does then it could be a cable problem, or a shifter problem.
If it doesn't then it's either a sticky mech or the limit screws are not allowing it to go over.
Is it a top or bottom pull?

 

[tom73]

Have you check with Calvin ?
https://www.parktool.com/en-us/blog/repair-help

 

[Ian H]

Bottom-bracket spindle too long?
Does the mech cage sit over the the chain if it's on the big ring, or does it not move even that far? If the former you might be able to bend the inner plate to push the chain across.

 

[Svendo]

Is FD clean? Caked on muck could be ‘extending’ the limit screw?

 

[Deleted member 1258]

Bottom-bracket spindle too long?

I was thinking that, has the bottom bracket been replaced at sometime? Whats the chainline like? Does the chainset sit a little too far out?

 

[Andy in Germany]

Thanks for the responses:

Undo the cable from the clamp and see if the mech moves across the full range by hand.

It doesn't

If it doesn't then it's either a sticky mech or the limit screws are not allowing it to go over.
Is it a top or bottom pull?

Pretty sure it isn't the limiter, although I'll double check tomorrow.

Bottom pull

It is also mounted on the BB itself with an odd plate between BB and mech. As this would push the mech out I can't see it's the cause of the problem.

Have you check with Calvin ?
https://www.parktool.com/en-us/blog/repair-help

Will look tomorrow, thanks. (Technically I'm being paid to do this so I may as well wait until I'm actually being paid)

Bottom-bracket spindle too long?
Does the mech cage sit over the the chain if it's on the big ring, or does it not move even that far? If the former you might be able to bend the inner plate to push the chain across.

Good question, I'll check the cage position but my impression was that it sits about halfway across the big ring at the most, even if pushed with a finger.

I doubt the BB will be changeable: it's a cheap collar and still pretty mucky.

Is FD clean? Caked on muck could be ‘extending’ the limit screw?

Entirely possible, although I think I'd have noticed that; will look tomorrow.

has the bottom bracket been replaced at sometime?

I doubt it, as it's a pretty cheap kid's bike and the BB fitting is filthy.

Whats the chainline like? Does the chainset sit a little too far out?

Will check tomorrow. It's a revoshift system and the rear mech is sprung to return to the big ring on the rear mech, and there's no cable to the rear mech, so I can't check the chain straightness...

From the state of the bike when it came in I wouldn't be surprised if this was a problem since it was new; it looks like someone has tried to fix it with the stop screws.

If I can't sort the mech quickly tomorrow it's probably not worth fixing even if I can get the BB off, as the chain and block are just worn enough that they are not connecting properly, so I'd have to change the mech, chain, and block. which raises the price by about 40 €

 

[Big John]

Hi Andy. We get a lot of this sort of trouble where I work too. We're always working on bikes that have been fudged by numerous owners before ending up at our place. Components are often mismatched and don't 'mesh' together causing problems like you're experiencing. We have an endless stock of used parts and simply try a different one. That usually does the trick. You get used to removing old and fitting a replacement in a few minutes so it's not as bad as it sounds. You seem to have tried all the usual tests so off with the old and on with the 'not so new' may be the solution.

 

[Ajax Bay]

Bottom-bracket spindle too long

This ^ Bit surprising given this is a child's bike so the BB would be the original.

The limit screw is unscrewed fully.

 

[Andy in Germany]

Hi Andy. We get a lot of this sort of trouble where I work too. We're always working on bikes that have been fudged by numerous owners before ending up at our place. Components are often mismatched and don't 'mesh' together causing problems like you're experiencing. We have an endless stock of used parts and simply try a different one. That usually does the trick. You get used to removing old and fitting a replacement in a few minutes so it's not as bad as it sounds. You seem to have tried all the usual tests so off with the old and on with the 'not so new' may be the solution.

I'll try but unfirtunately the mech is connected via a strange plate that is held on by the BB. I'm not convinced I'll get the BB off as it is a plastic attachment and absolutely gunged up.

 

[biggs682]

You have to ask is it worth the effort ?
It might be best just ditching whats on it now and starting afresh

 

[Andy in Germany]

You have to ask is it worth the effort ?
It might be best just ditching whats on it now and starting afresh

That's often the problem isn't it: where do you draw the line?

Here's the mech in all its ugliness. with the plate attaching it to the BB. To my astonishment I managed to get the BB off the bike:

It's a Shimano TY 30; 77/123mm long and in surprisingly good condition.

Question is, is it worth trying to find and fit a new mech?

 

[Andy in Germany]

Bottom-bracket spindle too long?
Does the mech cage sit over the the chain if it's on the big ring, or does it not move even that far? If the former you might be able to bend the inner plate to push the chain across.

I checked before dismantling and the cage couldn't move far enough to hold pull the chain; the pivot arm was striking part of the mech long before it could reach the stop screw

 

[figbat]

Would a band-on front mech do the job?

 

[Ian H]

I checked before dismantling and the cage couldn't move far enough to hold pull the chain; the pivot arm was striking part of the mech long before it could reach the stop screw

Might it be possible to 'adjust' it with a small file?