Front mech problem

[andyforse]

Fitting a new front mech yesterday (Deore) and I left the recommended
2mm gap between the outer cage and the big ring. Trouble is when
trying to move the chain to the big ring the inner cage catches on the
teeth of the middle ring. So I had to lift the mech about another 4mm
so it could clear it.

It seems to work OK but I wondered if anyone else has had this problem
or what might cause it.

Andy

[Sheldon Brown]

andyforse wrote:
> Fitting a new front mech yesterday (Deore) and I left the recommended
> 2mm gap between the outer cage and the big ring. Trouble is when
> trying to move the chain to the big ring the inner cage catches on the
> teeth of the middle ring. So I had to lift the mech about another 4mm
> so it could clear it.
>
> It seems to work OK but I wondered if anyone else has had this problem
> or what might cause it.

Shimano front mechs intended for triple chainset use are generally
optimized for a 10 tooth difference betwixt the large and middle
chainring. If you're going for a much smaller jump, as with a (yuck!)
half-step-plus granny setup, you'll get better results with a "double"
type front mech.

Sheldon "Decimalization" Brown
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[G Huang]

andyforse wrote:
> Fitting a new front mech yesterday (Deore) and I left the recommended
> 2mm gap between the outer cage and the big ring. Trouble is when
> trying to move the chain to the big ring the inner cage catches on the
> teeth of the middle ring. So I had to lift the mech about another 4mm
> so it could clear it.
>
> It seems to work OK but I wondered if anyone else has had this problem
> or what might cause it.
>
> Andy

I think the newer Deore FD is designed to work with a difference of 12T
between the big ring and the middle ring (ex. 44-32-22). Older cranksets
often have 42-32-22 or 44-34-24. I had the same problem after I replaced
the FD. In my case, lifting the FD another 4mm didn't work very well. I
had to replace the big ring.

[andyforse]

The chainrings are 22-32-42. Getting a 44 big ring just might be the
answer. I think I'll wait till it wears out or stops working first
though.

Thank you both for the advise.

Andy

[Chris Zacho The Wheelman]

>Shimano front mechs intended for triple>chainset use are generally opti
>ized for a 10 tooth difference betwixt the
>large and middle chainring. If you're
>going for a much smaller jump, as with a
>(yuck!) half-step-plus granny setup, you'll
>get better results with a "double" type
>front mech.

>Sheldon "Decimalization" Brown

"Yuck"? And here I thought you were my friend :-3(

May you have the wind at your back.
And a really low gear for the hills!
Chris

Chris'Z Corner
"The Website for the Common Bicyclist":
http://www.geocities.com/czcorner

[Shaun Rimmer]

andyforse > wrote in message
...
> The chainrings are 22-32-42. Getting a 44 big ring just might be the
> answer. I think I'll wait till it wears out or stops working first
> though.
>
> Thank you both for the advise.
>
> Andy

I'm running Deore front with 22-32-42. Lifted the cage to clear, angled it
'just so', and have zero problems shifting, well, that aren't related to the
(now) badly worn pivots on the mech (have to overshift a little, but it
worked fine for most of the year it lasted un-worn....).



Shaun aRe - Deore mech shortly to be replaced by an XT _conventional_ swing
type which will hopefully wear better than the awful top swing
types........).

[andyforse]

Those pivots do wear pretty quick don't they.

I'll get the XT myself next time, but I'm not sure if the conventional
swing will work with the Marin Rift Zone I'm riding. Whats the
difference between the two?

Andy


> I'm running Deore front with 22-32-42. Lifted the cage to clear,
angled it
> 'just so', and have zero problems shifting, well, that aren't
related to the
> (now) badly worn pivots on the mech (have to overshift a little, but
it
> worked fine for most of the year it lasted un-worn....).
>
>
>
> Shaun aRe - Deore mech shortly to be replaced by an XT
_conventional_ swing
> type which will hopefully wear better than the awful top swing
> types........).
>
>

[Shaun Rimmer]

andyforse > wrote in message
...
> Those pivots do wear pretty quick don't they.

Yup! 12 months average so far ;-(

> I'll get the XT myself next time, but I'm not sure if the conventional
> swing will work with the Marin Rift Zone I'm riding. Whats the
> difference between the two?

'AFAICR', the non-conventional ones were designed to bring the clamp band
lower on the seat tube to allow their use on certain full suss designs where
a higher band wouldn't have a place to fit (clamp band is below the mech
cage on these). The conventional ones have the clamp band higher than the
cage.

The 'conventional' low end Shimano (Altus? - dunno!) front mech I am
currently using just to keep the chain in place on the single front ring on
my FrankenBeater (commute bike) was still working (although not
fantastically) after about 8 years of constant use and abuse. The one that
replaced it (Deore top-swing) lasted less than 1 year before the pivots were
so worn it wouldn't shift unless I had all week to wait..........

Opinions I have solicited as to the comparative longevity of the two _types_
(not 'levels') seem to back up my experience(s). This is OK for me, as I
have enough room on my (HT) seat tube to mount the cage under the top tube,
if I so desired. You probably aren't so lucky, if your bike is an FS Marin,
but I can't picture the bike's design clearly enough.


Shaun aRe