Chain overshooting small chainring

brucey72

My chain occasionally overshoots the small chainring when changing down from the large chainring (I have a compact 50/34 and run a 12/25 on the rear) and I can't work out why its doing this. When I say "occasionally" it only happens maybe once every other 30 mile ride but it has got to the stage where I think about it every time I change from the big to small chanring and I can never get it to do it when my bike is on my workstand. I should also add, it seems to do it more often when going slowly and has happened more than once when I have changed down when slowing for traffic lights if that should make a difference.

I have checked, double checked and treble checked the set up of the front deralieur (sp?) using the Park Tools website and it is correctly aligned and indexing seems correct (I have a 1mm gap between the chain and deralieur when in large rear sprocket and inner chainring).

I recently bought a Deda Dogtooth but because the seat tube flares out towards the bottom bracket it can not be placed where it is supposed to go.

If anyone has any ideas why this might be happening I'd be really grateful.

dragonontheedge

It has to be a question of adjustment. I would double check the inner "stop" on the front mech.

I would suggest replacing the inner and outer gear cable as well.

Al

vs

http://www.wiggle.co.uk/k-edge-chain-ca ... n=products

Also available at other outlets.

Never had this issue on a 39 but when I changed to a compact I kept the same front derailleur which may have caused my problems. Anyway this is cheaper than a new FD and works great.

brucey72

@draggonontheedge, I thought the adjustment was the problem but the chain is only 1/4 turn of the adjustment screw away from touching the deralieur plate therefore I cant get it any closer without the plate actually touching the chain when in my lowest gear. My inner cables are changed yearly as part of a bike overhaul when my good bike goes into winter hibernation and the winter bike comes out. The current set only have about 400 miles in them as I have been off my bike for a long period following knee surgery so don't really think its the cables. I haven't changed the outers mind so changing them might be worth a try. Were you thinking along the lines of the inner cable maybe sticking? ?

@vs - I have a band-on front mech. Is anyone aware of something similar for this type of mech because, as I indicated in my previous post the seat tube flares where it joins the bottom bracket so a deda dogfang like device wont go where the instructions say it should go.

Thank you.

vs

I use a chain catcher on both my bikes and one is a band on, it works just the same.

brucey72

Is the one you posted the link to the one you use on your bike with the band on as I can't see how it will fit my front mech although I might just be missing the bleeding obvious.

I found this one but no way I'm paying nearly £40 for it:

http://www.wiggle.co.uk/k-edge-road-clamp-chain-catcher

vs

Yep, same one on both bikes, works a treat.

Here it is on the band-on FD.

John.T

vs wrote:

Yep, same one on both bikes, works a treat.

Here it is on the band-on FD.

That is actually a braze on mech with a band option. Not all are like that so there is no screw to fit the catcher to.

brucey72

[img][/img]
ebay 002 by brucey72, on Flickr

Thanks for the advice and taking time to post the photo. I'm sorry but i'm not sure what is meant by "braze on with band option" so thought I would post a picture of my mech - is this the same type as vs's?

You can just see the top of the cable tie which is holding the dog fang down onto the flared part of the seat tube/bottom bracket junction. Rather unsucessfully I might add so it will be coming off anyway.

John.T

Yes. Yours is is a braze-on mech with a separate clamp band. The chain catcher fits on the Allen bolt that holds the mech to the band. A longer bolt should be supplied with the catcher.

brucey72

Thank you very much John, that will save me a few quid

vs

That is actually a braze on mech with a band option. Not all are like that so there is no screw to fit the catcher to.

You are of course right - my apologies for the confusion :oops:

But at least the OP's is the same as mine

brucey72

vs wrote:

But at least the OP's is the same as mine

Although of a slightly higher spec Thanks for your help though, I have just ordered one.