Front Derailleur fit

[Cheule]

Hello all,

You may have seen my previous threads about upgrading my MTB parts.

Well, all is now done, new parts fitted, rear Derailleur done, front Derailleur, well, needs help. According to Bicycle Tutor, you should leave around 2mm between the Derailleur cage and the largest chainring. However, if I do that, the opposite side crashes into the middle chainring when trying to change up. Here's a couple of pics to show what I mean.

Top picture - see how high I've had to mount the FD?

Above - even though the FD is mounted too high as per normal specs - the inside of the cage still only just makes it over the middle chainring.

I've compared the cage with the old one it replaced, and the "cage" is much larger than the original especially on the inner side, causing me to have to mount the whole thing higher up the pole than I normally would.

Any advice welcome!

 

[Tigerbiten]

What size chainrings are you useing ??

I think you'll find that modern MTB front derailleurs need a 12 tooth difference between the middle and largest chainring.
If you only have a 10 tooth difference then they catch like yours does.

Luck ...........

 

[Cheule]

What size chainrings are you useing ??

I think you'll find that modern MTB front derailleurs need a 12 tooth difference between the middle and largest chainring.
If you only have a 10 tooth difference then they catch like yours does.

Luck ...........

Hi

The front chainring is 48-34-24T and the rear is 28-13T (8 speed).

EDIT: I should say I've moved up from 42-32-22T to the size above, also bought the Shimano FD-M591 front Derailleur to fit as it's supposed to support triple chainrings up to 48T.

 

[Tigerbiten]

Hi

The front chainring is 48-34-24T and the rear is 28-13T (8 speed).

EDIT: I should say I've moved up from 42-32-22T to the size above, also bought the Shimano FD-M591 front Derailleur to fit as it's supposed to support triple chainrings up to 48T.

With those chainrings it should be a good fit.
The only other thing I can think of is your seatpost is the wrong angle for the derailleur.
I cannot quite make it out from your photos, but the front of the cage looks a little closer to the chainring than the back.
If it is then that could be causeing the problem.

Luck ..........

 

[RecordAceFromNew]

I might be mistaken, but are you sure you have a 48-34-24 on?

I am asking because if that is the case the radii of the large (48) and middle (34) chain rings should be close to 3.8 and 2.7 inches respectively, i.e. the difference of which is 1.1 inches and which is more than the width of two "links" (or 1 inch, or distance between 1st and 3rd tooth). The photos show the difference in radius of the chain rings to be considerably less (which could have explained the clash). It could of course be illusion due to foreshortening for pictures being taken closeup, but perhaps you could check?

 

[Cheule]

Sorry about the pictures, I'll get some better ones up in a few minutes.

Oh...hell...I've just realised I may have made a boo-boo.

The crankset is a Shimano Tourney FCM-151.......48/38/28T not 48/34/24T.

I think I've fell foul of Shimano's 10T spacing rule

What to do...

 

[RecordAceFromNew]

Sorry to hear that. You have been very unlucky.

Since the chain rings of your chainset are riveted, changing chain rings is not an option. I am sure you would be loathed to have to buy a new mech or chainset.

It seems to me that if you set the mech position by aiming to have the inner plate to be as close to the middle ring as you can without hitting it, the outer plate should only be about 0.2" higher than what one would normally aim for. Have you tried it? It is not ideal, but it is not uncommon on bikes in the street. It might not shift as sweet as can be, but does it cause any serious problem in your case?

 

[Cheule]

I haven't taken it out for a ride yet but it's causing problems. The cage is contoured in such a way that the chain passes through it, but because I've had to mount it higher, the chain is hitting the inner contours of the cage in just about every combination.

I may just have to resign myself to getting a new crankset, this only cost me £12 new from ebay whereas the FD was £20.

Do you have any recommendations? Needs to be square taper though.

 

[RecordAceFromNew]

If I had followed Park Tool's guide setting it up and still having problems traceable to the chainset's range, then I would get another chainset.

IMHO all Shimano mtb chainsets having the right range are fit for purpose, and that the main difference between expensive (£350) and inexpensive ([url="http://www.chainreactioncycles.com/Models.aspx?ModelID=46025"]£27[/url]) is weight (~600 g vs ~1000g).

 

[Cheule]

Looks like I may get a Deore M590 or M591 chainset then, to complement the M591 front and rear mechs I currently have. Until then I'll have to ride to work stuck on the middle chainring...


EDIT...slightly better images (and the bike is the right way up this time)

 

[RecordAceFromNew]

Looks like I may get a Deore M590 or M591 chainset then, to complement the M591 front and rear mechs I currently have.

I believe these are not square tapered, so you will also need the tools for the bb's if you are swapping them yourself.

 

[Cheule]

I believe these are not square tapered, so you will also need the tools for the bb's if you are swapping them yourself.

You are correct, it's a Hollowtech II. Damn, I'll keep looking.

 

[Cheule]

Right, for now I've took off the new FD and put the seized old FD back on. Shame as the new one shifts lovely