front derailleur help

dazzzer

This is how I have been setting up my derailleur-I put the rear gear in the lowest cog and the front in the smallest chain ring , I then loosen the derailleur cable and then turn the barrel adjustment clockwise all the way round , I am not sure how to rest the limit screws so I just screw them down as much as I can , It says set to the inner plate and chain to 0-0-5m clearance this is what I have done using the L screw, Now I retighten the derailleur cable . I then put the front gear in to the middle chian ring, if it dose not move on to the ring I adjust using the barrel untill it moves , now I am on the smallest cog and larges chain ring I have noticed that even when using the H screws it moves a bit but could do with a bit more, I have been watching the chain in the derailleur and noticed that some links on the chain are very close and almost touch the derailleru but this only seems to be a few links on the chain and the rest seems to be ok with a gap not sure why.

nicklouse

read the how to on park tools.

but what are you asking.

How to set up a front mech?
Or
Why the chain ring does not run straight?

dazzzer

the problem i am having is with top adjusment -when in smallest sprocket and large chain ring the chain is ever so slightly rubbing on the derailleur . I have max out the H limit screw .

Chunkers1980

That has nothing to do with the limit screw. They are to stop over shift and sometimes rest on the lower. You need to double chech the height and angle of the mech. It needs to be almost perfect to stop any rub.

nicklouse

and maybe add some tension to the wire.

read the set up info on Parktools.

dazzzer

Chunkers1980 wrote:

That has nothing to do with the limit screw. They are to stop over shift and sometimes rest on the lower. You need to double chech the height and angle of the mech. It needs to be almost perfect to stop any rub.

The gears all work fine apart from when on the smallest cog and larges chain ring, It dose not rub on the chain Constantly but i can hear it sometimes is this normal as its the first time i have set up a front derailleur. Plus the H limit screw is maxed out and if i try and adjust by the barrel it puts the other gears out .

Chunkers1980

Are you sure your crank/chain rings are true?

A small amount of rub if you can put up with it can be ok. It's also quite good as you get to know what gear you're in via sound!

Front mechs are the hardest part of the whole drive train to setup, they are tempremental buggers at best.

dazzzer

Chunkers1980 wrote:

Are you sure your crank/chain rings are true?

A small amount of rub if you can put up with it can be ok. It's also quite good as you get to know what gear you're in via sound!

Front mechs are the hardest part of the whole drive train to setup, they are tempremental buggers at best.

Yup i spent hours on the dam thing already but its the first time i have tried to set up the front :twisted: I am not sure if the crank or chain rings are true is they an easy way to check this ? like said my bike has 27 gears and its just when on the smallest cog and larges chain ring it seems to rub a little but not all the time, when i start moving up the cogs when on the largest chain ring its ok then .

Chunkers1980

2 things to check, best done with the chain off. Spin the cranks and use a pen or something like that and hold it against the seat tube so it touches the outer ring and rotate the cranks and see if there is movement from side to side.

Also check for movement in the bottom bracket if it's a sealed one. If external type check the pretension, and again movement in the cups.

nicklouse

so what have you changed?

dazzzer

nicklouse wrote:

so what have you changed?

the answer to that is nothing ! I was hoping to stop all the chain rub but its not helped . I cant check yet but as someone said my chain ring might not be 100% true the manual says Set so that the clearance
between the chain guide
outer plate and the chain is
0 - 0.5 mm, not that would be very hard to do if the ring was out .

Shackster

You can't eliminate chain rub on the front mech in some gear combinations. Here's my way to optimise it (Copied form another post, on starting the set up from scratch):

In essence it boils down to:

1) set low limit screw so that chain just clears mech on granny ring/largest sprocket. Connect cable with moderate tension applied by hand.
2) Attempt to shift to middle ring - if it won't shift up you need more tension in the cable - screw the barrel adjuster out at the shifter. If it shifts up but then the chain rubs on the inside of the mech (while still in largest sprocket) you need less tension, basically because the mech is moving too far with one shift.

When you have done this, and you shift to the smallest sprockets (smallest 2 probably), you will get the chain rubbing on the other side of the front mech. You can't get away from this, it's up to you to decide whether you'd rather have access to middle/largest or middle/small without rub. You can get the same gear ratios (as middle/smallest) by shifting to the big ring (assuming you've got 3) and a larger sprocket.

You will never reach a condition where you don't get the chain rubbing on the mech at one or other side of the cassette. Unless you have a front shifter like the good old gripshift where you can tweak the front mech position whilst riding.

Hopefully, once you've done this you will also not have any chain rub when you are in the big ring and smallest sprocket. If you do you can increase the tension very slightly so it just misses.

nicklouse

dazzzer wrote:

nicklouse wrote:

so what have you changed?

the answer to that is nothing ! I was hoping to stop all the chain rub but its not helped.

all that was needed was a 1/4 turn on the cable adjuster to add more tension and maybe a tweek on the upper stop screw.

dazzzer

Ok I solved the problem of the chain that was rubbing on my derailleur! It seems it was not level now I set it 100% right all gears work with know chain rub, but after coming back from a bike ride I noticed very small plastic shavings, it seems my derailleur when its on small cog and largest ring one end of the derailleur it now rubbing against my chain guard , The strange thing was at fist I was leveling the derailleur using the chain guard as a guide to level but that didn’t seem to work, so as I moved the derailleur round more one end of the derailleur was touching a little on the guard .