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 Post subject: Front Mech
PostPosted: Thu Jan 07, 2016 4:12 pm 
Posts: 317
Afternoon folkes, how do, Ive been away for a while from the forum and riding but if I can get the bike to work then hope to get out ridding.

In the mean time i have a tech question im hoping you can solve.

A year or so ago I had the drive train replaced as it was worn, bent or broken. I replaced the old mixed spec OEM stuff with a shimano groupset. I then started having rubbing noises and put the bike to one side got xmas out of the way and then life got in the way.

Im now going over the bike and my issue seems to be with the front mech.

I was running a 3x9 as a double and bash with the limit screw wound in with 32 and 22 chainrings.
The crank was damaged and required cutting off the BB so replaced it with 3x10 still using a double and bash set up but larger chainrings. The front mech was also replaced.

The chain is now rubbing on the bottom of the front mech - the peice that joins the 2 side plates together - when im in the middle of the rear cassette. It looks like the mech cage is too short when viewed side on. i.e it doesnt go down far enough following the arc of the chain ring.

If the new front mech is the 2 speed version instead of the 3 speed will the cage be a diferent size? so would then be too small top to bottom to work with a double and bash set up? Ive got feeling that it should still need to be a 3 speed tbut with the screw wound down as i had no issue with the old one.

My logic being is that it looks like the front mech needs lowering, but if I do that it wont then be able to move over to the middle cog as the bash will obstruct it.


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 Post subject: Re: Front Mech
PostPosted: Thu Jan 07, 2016 7:37 pm 
Posts: 217
Location: Saffron Walden
Did you replace the front mech with another the same as the old one? Because with bigger rings up front your chain should be higher not lower, which sounds like it's something to do with the mech.

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GIANT TRANCE X 29er
BIRD AERIS


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 Post subject: Re: Front Mech
PostPosted: Fri Jan 08, 2016 8:09 am 
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Posts: 1405
Sounds like the front mech needs to be lowered down on the frame itself, is the ring sizes different to what you had before? what bash gurard are you running and what size is it and the rings ect

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RAF spitfire PEDAL-WORX RACEING


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 Post subject: Re: Front Mech
PostPosted: Fri Jan 08, 2016 12:16 pm 
Posts: 317
Ok so I had a better look last night - the pic shows where the chain is touching the cage when the chain is mid cassette on the lower ring.

It does look like it needs moving down but then the base will be in the way of shift to the middle ring.
The chaingrings are slightly bigger but comparing it to the one on the mrs 3x9 bike the old mech that would not be an issue as hers has a plastic guard on the large ring tha same size as my bash

I am fairly sure that it is a 2x10 specific mech which would be fine on a double but because i have the bash i need a 3x10 as it would have the longer cage? and clear then bash?

The new one looks to has a shorter cage than the old one and the mounting clamp is further up the seat post tube than the old one was.

If thats the case then its a new mech thats needed?
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 Post subject: Re: Front Mech
PostPosted: Fri Jan 08, 2016 12:54 pm 
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Posts: 1165
You probably had a bottom pull/conventional front derailleur before, so you need to get another one of them that has a clamp band that matches your seatpost diameter and also a cage that can cope with the biggest chainring tooth count/bashring size. The outer edge of the cage should be 2 - 3mm from the teeth on the largest chainring.
Something like http://www.chainreactioncycles.com/shim ... -prod83152 might work.


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 Post subject: Re: Front Mech
PostPosted: Fri Jan 08, 2016 2:54 pm 
Posts: 317
Thanks, its definately a topswing rather than the conventional as the reason i left it to the LBS is I bought the type in the link and i have a bottle boss right where the band needs to go.

As CRC have such great returns risked getting the top swing version of the one in the link this morning,
Will offer it up before fitting tto make sure.

I cant believe shimino has 5 diferent m671 versions. 4 hours of websurfing to determine the correct one.
Thanks for the assitance


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